Engine health "blow-by test"

This is a simple test, but very accurate at determining the blow-by of your M96 (or any other) engine. If you really want to keep track of the health of your engine, this test is for you.This test is so accurate it is un-useful in most diagnostics of sudden problems/failures (compression test and leak down test are best for them) , but is the "best kept secret" of top engine builders of high end engines for new engine development/piston ring combo's and long term wear maintenance engines ( ie Marine engines ect).. Step 1 . Drill a precision .221hole (also known as #2 dill in numbered sets) in your manometer test cap like shown below. Step 2. remove AOS hose at the intake and plug both sides, the intake side (.860 ID) and the hose side, (.640 ID) Step 3. start engine and observe manometer reading in inches of water.( inh2o). Refer to chart to translate inh2o to Liters-per-min of blow-by..to convert to CFM multiply LPM x .03531 I thought I would include this test here after a forum member who is interested in the UAOS was discussing his manometer reading of the usual AOS test with me and it was reading a POSITIVE pressure of +30inh20, where a failed AOS will read a high NEGATIVE (vacuum) pressure. I would like all my UAOS DIY License holders who have manometers to do this test, or anyone else who is interested in keeping a good watch on engine health. An increase in blow-by can only occure as the engine gets tired/wears down , or has "bore scoring"... As a reference my 99 3.4 has +8 inh2o = 81 LPM (2.8 CFM) of blow-by at full load WOT ,with 177k miles and is typical of what to expect.. I decided to include instructions for doing a blow-by test at idle speed, since it is more easily performed (maybe more people will do it) and since the blow-by will be worse as a "percentage" at idle. Higher engine speed means less time for blow-by to escape past the rings, and more load (WOT) helps the rings compress against the cylinder wall thereby creating a better seal. Blow-by hurts torque more than it does top end power. The "volume" of blow-by will be higher at high speeds/high load, but the "percentage" of blow-by (vs air intake ) will be less at high speeds/high loads.. So testing at idle speed not only will be easyer, but will be more meaningful and more differences can be seen between engines. The test is done the same way, except instead of using a .221 orifice at WOT and max torque speed (4600rpm) , we use a .110 orifice at idle speed and the chart figure number for LPM is divided by 4 giving the actual LPM of blow-by at idle speed. example: on my 3.4 177k miles engine, at idle speed with the .110 orifice the manometer reading is 4 inh2o , the conversion chart says 58 LPM / 4 = 14.5 actual LPM of blow-by at idle speed. Not too bad for that kind of mileage. Showing .110 idle speed test orifice vs .221 WOT test orifice Both orifices plugged to use manometer as usual AOS tester. Get precision .221 #2 drill bit here ?>> Amazon Amazon Amazon Amazon Get precision .110 #35 drill bit here >> Amazon Amazon Amazon Amazon Get plug kit for hoses and oil cap tester here >>> Amazon Amazon Amazon Amazon

Thanks DOC! Just a side note, manometer testing should be done on a fully warmed up engine (I did not know that) and my test was done after a 1/4 mile run and I was not up to proper temp. Will retest, Stay tuned! Also, Vertex (bait n switch?) sold me an after market AOS when I ordered a Porsche Brand advertised on Amazon for my 02 996 last year...Vaico was the brand of my 6 month old AOS that showed erratic readings when mano testing. Vertex made it right but it was a HUGE inconvenience ( twice they sent a Boxter unit before they got it right) and caused me 2 weeks of down time and aggravation not to mention having to do this again in such a short time. I understand the P brand can fail right out of the box too, but I think that rare from what I've read...Todays PSA, buyer beware!

Now on a brighter note, the new AOS seems to have alleviated my high crankcase pressure! Got to work and not a drop of oil on the ground or on the motor. I was getting a couple of table spoons on each bank. Will continue to monitor it...

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So what does your AOS manometer test show NOW?

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I buttoned everything up last night and never had a chance to test (at work today) yet. Two eight hour days working on this and I'm spent...Did injectors and starter also.

I've got a sack full of these little 6mm x 3mm Silicon rubber plugs to seal the precision .221 hole in your AOS manometer test cap. I will start putting one in with the UAOS mounting parts bag on all new orders, so you can install the plug to use as regular AOS test , or remove the plug ( and cap the AOS hose) to use as a "blow-by" test. If you want one of these plugs, you can get a sack full on Amazon for $5 bucks, or send me your address and shipping cost of $1.10 and I'll send you one. They are handy for other things as well.

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I think I need to visit the eye doctor -- this is making my cataracts hurt

Gotta say, whatever engine you show in your first picture needs a serious detailing, for shame. Oh, wait, that;'s my engine Can you throw a plug in my parts bag? Right after i made an appointment with the optometrist i remembered you have a lousy phone camera,

"As a reference my 99 3.4 has +8 inh2o = 81 LPM (2.8 CFM) of blow-by with 177k miles and is typical of what to expect.." Is there a reference table to compare blow-by vs engine miles to see if a car is within expected range or has excessive blow-by?

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lol,,yea I know my camera sucks, maybe someone will feel sorry for me and send me a good one?? I figured you would recognize that pic, you can clean it up while you are installing the UAOS !! (Sure i'll drop you one in the bag ) I can say for certainty that +30inh2o (157 LPM) is way too much, especially at idle. My +8inh2o ( 81LPM) was done at full throttle with the manometer set to record and laying in the engine compartment. All engines can be different in blow-by amounts depending on how well they sealed up on break-in..There can be quite a difference and still be OK. It's kinda like the info gained from oil sample sent to a lab for UOA, it's better to have a trend from new,( because the accuracy is so great, the differences can be large and still be OK).then monitor the wear (increase in blow-by) Top Engine Builders use blow-by data to test cylinder finish/ring pack sets to try to get the lowest blow-by possible for engine development. Less blow-by = more power. That data is never reviled and they use it to develop their own engines and is a "Trade Secret".. Marine engine Technicians use blow-by test to determine when to refresh an engine, when the blow-by is twice the amount from new, it's considered time to refresh. If enough forum members would do the test, it would be easy to chart the "normal ranges" for miles driven with enough data. But from what I've seen, the forum members are too lazy to do the tests, they just want to know what to expect without contributing to the data. There is no charts, ( but one could be made) just like there is no set data on UOA analysis. Like how much silicon ppm is when I know I have bore scoring? I'd be really surprised if enough data can be collected to form a comprehensive M96 blow-by chart..

And more than a few of us have non-stock engines so that would certainly skew the data as well, depending on the builder and how it was broken in. Looks like the value with this data is just to monitor a car's health over time. Or maybe get some snapshot data points on different mileage cars, like you did with yours, and maybe see what that looks like overall. I'll run the test when i get my car all put back together. I'm certainly going to run the AOS test as a baseline on my UAOS.

Skip, I'll do my part. as soon as I get the #2 bit. Put my name on one of those plugs!

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Yes it will be interesting to see the blow-by data on the non-stock engines as well. Who built yours and what mileage do you have on it? Thanks Bill, I can always count on you. I got a plug with your name on it ..

Flat 6 Innovations, about 26k since rebuild.

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Ahh, just getting broke in good, probably will be hard to measure any blow-by, .(.oo1inh2o?) BTW;; your UAOS shipped today, I'll e-mail you the tracking number

I hope so Been treating it well, 6 mo oil changes, DT40, etc. But the failed AOS has me a little concerned about any potential internal issues. My inh2o reading was thru the roof.

Great tip as usual Doc! I'll get a reading once the weather warms up

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Thanks Joe, BTW, your UAOS shipped yesterday, check your e-mail for tracking #.. Signed, Dr. h. c. Porschetech3

WooHoo!

Here ya go Bob, found this while poking around on the net, a generalized chart for blow-by, while I usually use my own data for my engines only, this is for general application, and confirms what I already know, if an M96 has over 4 CFM (115 LPM or 17 inh2o crankcase pressure) it is due for rebuild or has cylinder/ring problems. Customers frequently ask what are the typical Blowby CFM flows they should expect from their engines, and what is too high. The equations in the table below should let you make this VERY APPROXIMATE estimate. The actual blowby level and acceptable blowby limits will vary greatly between different engine manufacturers and engine applications. Application Equation for Typical Blowby Equation for Blowby Suggesting Rebuild Used Motor, "workhorse vehicle" .01 x Peak Tq (ft lbs) .02 x Peak Tq (ft lbs) Modern production motor .005 x Peak Tq (ft lbs) .015 x Peak Tq (ft lbs) " Tight" racing motor .0025 x Peak Tq (ft lbs) .0075 x Peak Tq (ft lbs) For example, if you have a modern production vehicle (naturally aspirated, turbocharged, most anything) which has an advertised peak torque of 300 ft lbs, it will likely produce about 1.5 CFM of blowby (300 x .005 = 1.5). You would consider the blowby high, indicating the rings may be bad if the blowby was over 4.5 CFM (300 x .015 = 4.5 CFM). Still would be nice if we had our own chart.

So the peak torque on my engine when built was 262 ft lbs at the rear wheels from the Dynograph. Or do you think they mean at the flywheel (20% higher since it's a Tip = 314 ft lbs). So .005 x 314 = 1.57 CFM. So will be interesting to see what it is when i get a chance to test it, after the UAOS goes in.

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Correct !! 1.57 CFM = 44.4 LPM or 2.5 inh2o at WOT @4600rpm ( max torque ,with .221 orifice)

I decided to include instructions for doing a blow-by test at idle speed, since it is more easily performed (maybe more people will do it) and since the blow-by will be worse as a "percentage" at idle. Higher engine speed means less time for blow-by to escape past the rings, and more load (WOT) helps the rings compress against the cylinder wall thereby creating a better seal. Blow-by hurts torque more than it does top end power. The "volume" of blow-by will be higher at high speeds/high load, but the "percentage" of blow-by (vs air intake ) will be less at high speeds/high loads.. So testing at idle speed not only will be easyer, but will be more meaningful and more differences can be seen between engines. The test is done the same way, except instead of using a .221 orifice at WOT and max torque speed (4600rpm) , we use a .110 orifice at idle speed and the chart figure number for LPM is divided by 4 giving the actual LPM of blow-by at idle speed. example: on my 3.4 177k miles engine, at idle speed with the .110 orifice the manometer reading is 4 inh2o , the conversion chart says 58 LPM / 4 = 14.5 actual LPM of blow-by at idle speed. Not too bad for that kind of mileage. Showing .110 idle speed test orifice vs .221 WOT test orifice Both orifices plugged to use manometer as usual AOS tester. Get precision .221 #2 drill bit here ?>> Amazon Amazon Get precision .110 #35 drill bit here >> Amazon Amazon Get plug kit for hoses and oil cap tester here >>> Amazon Amazon

Test at full operating temp right?

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Yes, blow-by will be worse until full operating temp is reached..

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That�s usually not a bad thing. With my gapless rings, and a totally sealed up engine with around 30K miles on it (just finishing the break in) and etc, its totally normal to sometimes have readings off the chart. None of the data people post here will pertain to my engine~, and each one of them will measure differently.

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Hi Jake, thanks for weighing in on this subject, your experience/knowledge carry's a lot of weight here. Since many of your engines use the Factory AOS with no issues( unless the Factory AOS fails), they will also be able to use the UAOS (which is a better design) and even have better control by keeping an eye out for potential oil accumulation by the infra-red sensor in the Accumulator, with no issues. Since I have a vested interest in the UAOS, anything that can effect the blow-by flow above what the Factory AOS or the UAOS can handle, needs to documented. The value of the blow-by test is to identify engines that still have useful power, but the blow-by flow has increased due to wear or cylinder ovaling and if the blow-by has increased enough it could cause excess accumulation and frequent triggering of the warning system. while this hasn't happened yet, it is anticipated and the data should be ready to identify it. As an example : my engine has 14.5 LPM blow-by at idle and 81 LPM blow-by at WOT at max torque, and any blow-by readings of less than that will have no issues with a "good working" Factory AOS or with the UAOS. But more data is needed to see how much more blow-by can be considered acceptable.. My main interest/focus is helping Porsche people get the most useful mileage out of their M96 engines, that is an exacting Science as well.

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I presumed your engines wouldn't "read" like a stock engine since they don't "drive" like a stock engine :-) Not the same engine, that's for sure.. I was thinking about testing the blow-by just for a "baseline" and curiosity. I expect it will be very low, and now after reading your comments, much lower than standard. I still suspect a failed AOS since the oil consumption has increased quite a bit over the past 18 mos and I'm seeing soot on the back bumper and it seems like there's a pretty high failure rate on the newer AOSs. I have just received PT3's UAOS and hope to get it installed over the next week or so, back pain willing. Also cleaning out the intake manifolds to make sure no oil collected that could hydrolock the engine.

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Yes, another very good reason to do a blow-by test , for the individual to "base-line" the engine..

One of our Rennlisters here had a suggestion, his well seasoned Indy just installed his UAOS kit (with no problems what so ever), but he didn't have a manometer , and didn't want to buy one ( since he works on various models and not specifically Porsche 9xx models) or source the pieces and take the time to build one, they wanted to "rent one" and suggested I provide the service. So I agreed, it would be a good service for someone in the same situation. Here is the deal, I will rent the manometer shown for $50 bucks + shipping, and if you buy the UAOS within one month I'll give a $25 discount off the price of the UAOS . A deposit of $199 up front will be refunded except for the shipping cost and $50 bucks. This manometer is highly sensitive,(0-2psi and 0-54 inh20 range + 11 more modes) will test AOS function, and also blow-by at idle, and blow-by at full throttle. Has Min/MAX Record function. Has the precision .221 port , and the precision .110 port plus the correct rubber taper plugs to plug the AOS tube and intake port for blow-by tests. Oh, and BTW , my picture skillz have improved !!

You get a new phone camera? Or just steadier nerves :-) I'd be interested in using this after i finish my UAOS install. I'd like to get a benchmark on my engine. That would be less expensive than an hour of shop labor for my indy to do it.

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I got a "real" camera thanks to Scott !! He picked me out a good simple point and shoot camera that can be used by people who no idea about photography..an old dog that can't learn new "tricks". Since you have already purchased the UAOS, you can get the "special" on the Manometer !!

That Scott is almost as good a guy as you are, Doc.

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I just found my old point and shoot and was going to stick it in the mail to you. Good to hear you�re all sorted.

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Thankx for the thought !!!

Infrequent poster, but I did this sounded like an interesting test. 2004 C4S manual. 100,400 miles Went for a 1 hour drive, then ran test at idle in driveway. Blow by:. +3.12 in w.c., so about 49LPM = 1.73cfm ​​​ Blow by test. The AOS line is plugged, both sides at TB. Engine at temp. At idle: 800rpm 0.110 in open hole in cap. = +3.12 inwc pressure I took an AOS test at the same time (reconnected AOS hose, plugged hole in cap), and got -4.40 inwc. The value seems good (<5), but is the sign correct? A slight vacuum in crank case? I think so, as gasses are being pulled into the intake, but I wanted to make sure. AOS test. AOS line connected. Cap plugged. Engine at temp. At idle:800rpm. = -4.40 inwc Used a Dwyer 447-2-FM manometer. Open port is reference, so in this case it's open, just standard atmosphere reference 1. Also, my precision 0.110 inch drill bit actually measures 0.109 inches on my micrometer, if that 1% error matters.

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Yes, there should be a slight vacuum in the crankcase, the -4.40 inh2o is correct value. You should also test it again to make that value is reached instantly, we recently had a Rennlister that did this test and it took 20 seconds to reach the correct value indicating a delay in the AOS function. Also the conversion chart is for a .221 orifice for WOT blow-by, when using the .110 orifice at idle, divide the LPM by 4 (.110 has 1/4th the area/flow of .221), so your 49LPM is actually only 12.25 LPM at idle speed. Your 3.6 with 100k has less blow-by(12.25 LPM @ 800 RPM) than my 3.4 with 130k (14.5 LPM @ 800 rpm) Thanks for posting your data point !!

Thanks for the reply! I divided by 4 on my initial notes, but then forgot when writing up the post. Doh. Glad to see my engine is in the right ballpark. Thanks again for this test. Between your UAOS, this, and your help all around the forum, I'm learning alot. Lurking mostly..., but learning. Thanks.

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Thanks for the kind words Sir !! And continue to keep posting !!!

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Great data points. Thanks for sharing. With enough data points, this could be another great test to regularly monitor and evaluate engine health very easily.

I have a device that plots positive or negative crankcase pressure. It is basically a fancy manometer that also reads volume, and not just pressure changes. I learned a lot with this, that the manometer would not show, especially in changes in response, not just changes to the values. That said, what I see drive changes in these readings the most, with the fastest changes is fuel enrichment. Years ago I was able to see this first hand, and it continues today. As soon as an engine becomes over- enriched you can expect crankcase pressure changes to occur within 100 miles. Been there, and done that with multiple engines. The factory cylinders, and pistons hate enrichment, and the OBDII system has a good way of masking it. A stand alone AFR meter tells a completely different story. This said, the more the cylinders have lost seal, the lower the manometer reading becomes, and the positive pressure that's being created ends up cancelling out the negative pressure from the AOS. I have seen engines with a failed (conventional) AOS that didn't show signs of AOS failure, because the cylinders had lost seal. Change the AOS, and then the engine eats oil, and starts to show the symptoms that it should have shown beforehand.

I have no idea how I missed this thread. Just ordered some plugs from Amazon and will test mine ASAP. Would I be able to remove the UAOS diaphragm and plug both lines (going into the diaphragm and into the TB) and get the same results, or would the missing diaphragm skew the results? Or perhaps remove the diaphragm from the rubber hose going to the TB, rotate it and plug it and the rubber hose going to the TB. I could also disconnect the plug going to the EVAP purge valve, or pinch that hose where it enters the TB.

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Great thread! Major popcorn cooking for this one. Link?

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See links above^^

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Glad I got even close to almost.

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Great post. Only one small thing. That's actually 0.1% So that's a pretty good drill bit. I'll get my coat.... I'm going to need it, it's not going to be above 45 F today.

Ok Doc, I'm doing something wrong. I don't have a fancy-smancy digital gauge, only a homemade slack tube, so precision is limited. I had car totally warmed up. Blocked off the tube, and the opening into intake. #35 hole in cap. Measured 1.3" h20. If using your chart, the closest is 1" (27LPM) Corrected for the additional 0.3 would be 31LPM. 31/4= 7.75. This can't be correct for a engine with 78K miles.

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I duno, it's been here for a while now. I hope more people see it and it helps sell UAOS's!!!. Right now I'm only selling 1 a day, it will take 54.79 years to reach my goal of 20k units..lol, I'll be long dead by then, and will not have made a dent in the reliability of the M96.. Yes, you can disconnect the UAOS flow regulator on either side or remove it, as long as you plug both ends going and coming. The purge valve is only activated on certain conditions, but to be safe as not to skew test, you can just disconnect it at the quick-connect and plug it..

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Yea, you're doing something wrong. Is your AOS test value low also? If so, you better smoke test to find a leak somewhere like the oil fill tube ect.

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Nope. AOS tests at 5�h2o. I even double checked it after the blow by test. I disconnected the line from the AOS to intake, as instructed, and plugged the end of the hose with a stopper, and the hole where the pipe connects to the intake with another plug. Car was warm after a 30 min drive. Sitting at idle. What am I getting wrong?

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Bring it over to the house tomorrow and I'll figure it out !!! There's always someone with an unusual case !! lol

Doc, I would genuinely love to do that! Stole the pic, but here is what I plugged

...and yes, I broke down and ordered a digital manometer today

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Thanks. I love quantitative tests like this. But... (0.110-0.109)/0.110 = 0.001/0.110 = 0.00909 = 0.909% ~ 1% (I rounded. No need to get too precise here!) Thanks for checking my work! Love your build by the way.

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DOH! Thank you for the refresher.

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You could have had the purge valve activating while testing an caused some blow-by pressure to leak out the carbon canister, skewing the test !! Was the purge valve "ticking" during the test??

I don’t remember the purge valve ticking, but can’t say for sure. I did notice a bit of oil in the vent line of my slack tube manometer, so it may have been adding resistance. I’m going to test again. Thanks Doc

I hope I am not hijacking this thread to ask a Manometer question. I bought a $35 Manometer from Amazon and I connected to the brass connector I installed on my oil filler cap. I'm getting 3.3-3.4 in/H20 reading. Should I be getting a negative value or are the positive and negative considered the same for this reading? Boxster 986S was fully warmed up. Thank you. Here is unit: Digital Manometer, Dual Port Air Pressure Meter Pressure Gauge HVAC Gas Tester, Differential Pressure Manometer with 5/16 Inches Diameter Pressure Port, Hti-Xintai Amazon Amazon

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Should be getting a negative value

So should there be air coming out of the oil cap brass nipple or should there be air being sucked into the brass nipple? Reason I ask is: If I blow into the Manometer (very slightly), I get a negative number but if I inhale (avoiding the word I should use) on the tube (very slightly), the number is positive. Also Porschtech, I have a 986S Boxster and sounds like your UAOS is designed for the 996, that's why I have not ordered. Thank you!

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You have a Dual Port Manometer, and have the sensing tube on the wrong port.. Yes the UAOS is designed for the 996, I will be broadening the coverage to include the 986/987 later this year..

Thank you Porschetech. I switched ports and yes, you are correct. Now I am seeing a negative value. Appreciate the tip!

So, with a huge thanks to Doc, I found my issue. Purge valve not working. Plugged it off and got a proper reading! Measures 3.26 inh2o, so 12.8 LPM blow down. Ive around 80K miles on a 3.6.

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Thanks for Posting your data point !! The 3.26 inh2o 12.8 LPM is what we would expect.. Glad I was able to help you figure out why your test values were shewed !!! The purge valve stuck and leaking was allowing blow-by pressure to escape all the way back to the Carbon Canister in the front fender. It would also be allowing air to leak into the intake and cause lean running condition, I'm surprised you haven't had issues with that... My 45 years as a dealer Technician, most was spent as a specialist in Driveability/Electronics/ Engine Management so this stuff is my forte.. BTW :: you also are using the wrong port on the Dual Port Manometer., just as sequel95 ..The negative symbol " isn't real important....until it's real important !!"" The Manometer reads values above and below Atmospheric pressure..( Atmospheric pressure being 0 ) so to be 100% perfect and confident and exactly correct, use the correct port.... Thats why on my loaner/rental Manometer, I chose the Single Port Dwyer , there is no need for the DUAL Port on these simple tests..

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I caught that too. Realized the negative after taking the picture and swapped the ports...same number only no -

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Single port so no user error? You knew I'd be using your set-up, didn't you

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Exactly !!! I want no user error !!!!!

Here's my contribution to the thread. '99 C4 Cab with 34,600 miles. Original AOS. Normal AOS Test Updated picture with the AOS line blocked at the intake. What is the significance of a negative number here?

Whoops! I need to disconnect the AOS line to the intake and block both ends. I'll retake the readings later this weekend.

Any time I see a manometer reading less then 4.00, I get very concerned with ring seal, and engine mechanical integrity. I really start to become concerned if the value is less than 4.5, but changes in atmospheric conditions can come into play, and we start splitting hairs. Over the 18 years I've been gathering this data these values can usually be met with excess blow by if the AOS is no longer allowed to pull a vacuum on the crankcase. The blow by helps to partially neutralize the vacuum, resulting in a low manometer reading. Lots can be learned by taking these values with the AOS attached, and then with it disabled. Not just in the values that are noted, but also with how the values behave at different RPM, and at different temperatures/ loads. I have a 50 year old manometer made by Fisher. I use it as a back up to the digital meters, because I can see the behavior of the needle, and get a better visual of the behavior than I can with something digital. Its a lot easier than having to set the blow by data logger up on every car, I save that for development, or in case we have a problem and need to plot Vs RPM, load, or temperature and record back to back. The manometer data is some of the most critical information that can be deciphered about the internals of these engines. If you want to see almost immediate results of changing enrichment, and how it effects cylinder seal, the manometer is the best tool for this. Tony Callas and I started instructing techs at our classes about gathering this data back in 2008. Back then it wasn't something that was common place at Porsche shops. The procedure was robbed from BMW, and Tony and I took the trend data that we had gathered over the years to determine the optimum values. A big disclaimer to those who have my engines, the values discussed within this thread do not pertain to your engine, our values are WAY different than those discussed here. Your readings may be off the scale, and be both normal, and expected. Total Seal Piston Rings, Nickies (with my RA), and adding hundreds of ccs of displacement all make their impact.

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Making sure my contribution is not lost.

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Normal AOS test should be negative (vacuum pulled from intake) and crankcase blow-by should be positive.(Air from combustion forced past rings into crankcase). Your signs are opposite, so it likely means that you have a dual port manometer, and your tube is attached to the wrong port (to the reference instead of to the measurement). Porschetech3 or someone else will have to weigh in, but your Blow-by of only 1.83 inwc seems strangely low compared to others. Maybe they can advise on double checking your test method. JTT posted above that he measured 1.3inwc, but Porschetech3 helped him to discover that the purge valve was activating during the test and influencing the results, but I don't really know one way or the other; just my 2-cents.

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I'll rerun my test today after switching the manometer port. Where is the purge value located and how do I block it off?

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Any part you buy from a Porsche dealer is warranted for 2 years.

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Check the pic here, this is the usual setup for all 996 except for 99 C2. The 99 C2 has the purge valve connected to the other side of the TB and not to the AOS breather hose.

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Yup, follow the hose from the purge valve in PorscheTech3�s picture to the intake. Disconnect the hose and plug the port into the intake. Then take readings again.

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Jake, when you say �4.00�, is this measured in the manner being prescribed? (with .110� hole, at idle, AOS ports plugged) I was thinking with this reading �less is more�, with higher readings indicated greater blow by, indicated greater wear?

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Does the '99 C4 have the same setup as the '99 C2?

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Nope, the 99 C2 is the only one with cable TB, the 99 C4 is like all the E-Gas models.

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Thanks for the insight Jake. Just to add a bit more insight, this technique for testing engine blow-by is an "old school" technique using fixed orifice and manometer pressure readings with a new application on a modern "closed and sealed crankcase ventilation system. The "old school" crankcase ventilation systems were either fully open or fresh air circulated crankcase systems and would require a lot of preparation to completely close and seal the crankcase system before the fixed orifice and manometer blow-by tests could be done, but this technique was done by Volvo/Penta Marine and used to evaluate engine health and rebuild schedules. Back in that day, there were no "flow meters" except in Laboratories and they were huge and not used in field service, so this technique serve its purpose for accurate blow-by data, even though it took a lot of prep work to close the system. This technique is even more easily used on modern closed systems,in the M96 the crankcase is already designed to be a closed and sealed system it only has to be disconnected from the intake and plugged. The fixed orifice and accurate low pressure readings of the Manometer translate to accurate blow-by readings in a simple non expensive method. All different engines will have different blow-by values, generally varying by torque output, but when getting more accurate a lot of things can be envolved. Competition engine builders are constantly trying new pistons/ring packs/ cylinder finish to get the lowest blow-by and less drag to create the most power. That's why I say "blow-by data is the best kept secrete of top engine builders".. Manufacturers are also trying for the lowest blow-by and drag, but for different reasons. Low blow-by is good for emissions and less drag is good for fuel mileage, and that does correlate to more power, but is not linear. The simple AOS test should be done periodically, it is so simple and easy. (literally remove oil cap , install manometer , get readings). The blow-by test is slightly more prep (disconnect the hose and plug, also the purge valve), but if you plan to keep the car long term and closely monitor it, then this is for you.

Final numbers are in for my '99 C4 with 34,700K AOS reading Blowby reading at idle

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Your reading of 4.49 inh2o coverts to 15.25 LPM blow-by..at @ idle speed Thanks for posting !!!

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Are these numbers typical for a motor with that many miles? The car is not consuming oil and pressure seems to be pretty solid though the guys at Intersport Performance, in McLean, VA, said there was some blowby and the AOS should be replaced. ​​​​​​​

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Like I discussed previously, this test is extremely accurate at determining the actual blow-by of your engine. So accurate in fact that it is almost useless as a tool for diagnosis of a problem. (leak down tests or compression tests are best for that).. The data over time is what is important at evaluating an individual engine, and the data collected as a whole for same engines built to same specs. We need much more data points from the community to make educated analysis of any particular data set. No data on this subject has ever been available from Porsche (but you know they have it )... Using general knowledge and the SWAG method (Scientific Wild *** Guess).. I would say that a blow-by reading at idle speed 800rpm of over 20LPM would be cause for concern..We have a few data points of 12.25LPM 12.8LPM,14,25LPM, 15.25LPM much more is needed. Your data point of the highest blow-by reading so far(15.25LPM) and the lowest miles (34K) is very interesting in that regard, but no cause for concern. It is well known that some of the modern design engines with low tension rings/special cylinder finish/ synthetic oils , do not achieve full ring seal/lowest blow-by readings until after 30k miles. Like I said ,data over time is the most important.

So I had to makeshift plugs for the AOS hose and TB connection and am concerned they are throwing off my values. Idle was stable though. I used sockets wrapped in latex glove for plugs... Any clever ideas short of the silicone plugs - ordered today That said - I got +1.40 in/h20 My setup:

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+1.40 inh2o is not plausible. I think you need to also plug off the purge valve. See post #75 above for identification of purge valve and location of the quick-connector.

I can plug the hose coming from AOS with the quick disconnect, yes ?

Quotes source post: 16832683

You have correctly disconnected the AOS breather pipe quick-connector and plugged both ends. Now you need to disconnect the purge valve quick-connector and plug the side going to AOS breather " y" connector, or both sides is OK too.

So, I took another run at this after taking the wife and kids for ice cream. Here is a pic of setup, I believe I plugged everything required. The car has cooled slightly since last test but still operating temp. Same result, +1.40 in/h2o. Smooth idle.

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Yes, that is the proper set-up. You definitely have another air leak. I would assume the AOS crossover pipe where you have seen oily residue is where the leak is. BTW ; Your UAOS is boxed and ready to be shipped tomorrow..

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Well... I guess we will be retesting when everything is back together... and crossing my fingers in the interim. I have a replacement crossover pipe in the box of other stuff I'll be replacing when I'm in there. Really appreciate you expediting the kit, thank you.

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This is a really good test of engine health and is easy to do on the m96 engine. I spent a little time developing this test for the good of the 996 community and was hoping for more involvement. At the Porsche dealership, most of the 996's that were brought in were "like new" low miles and in great health or had an early unusual failure/ problem. And at a facility like Flat Six, broken motors are mainly what he see's, so all the great data that could be obtained for engine health in all the cars out in the wild that are driven by members here. Indy's probably are not aware or set up to do this test, and if they were it would probably only cost about $100 bucks for them to do it. But you can DIY it yourself if you have the simple set-up. With over 5k "views" and only 4 data points, it seams lots of "readers interest", but not many actually getting out of the Lazy-Boy Recliners or off the couch to go into the garage for an hour to spend some quality time with your baby.. I promise you will become more intimate with your "baby" if you take the time to know the true health of her, and she will appreciate it, or at least not mind..

Ill get u some numbers from my 200k mile car as soon as i get the stupid ps return line leak.

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Cool man, every data point will help, especially on 200k up cars !!!

What is the difference between the black oil cap and the yellow oil cap if any? I have several manometers so I'd like to try this out to see what reading I get. Have to change the oil filler tube first (that I broke).

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The black cap is a newer verion, it is a little different underneath but either one will work, just pay attention when putting in a fitting so there is no interference.

Porschetech, I was going to order the 0.110 drill bit to do this test, but Amazon stated it will take 2 months to arrive! So I thought, why not use a 2.8mm or 7/64 drill bit that are more readily available?

I didn't know they had back-ordered the #35 drill bits, yes, those are "very close" alternatives. BTW, thanks for the detailed conversion chart !!

Bump for a good thread. Several people seemed to have it on their list of things to get to. I'm wondering if anyone else has been able to measure theirs?

I'm trying, I'm trying, but I'm out of the country. Not back until December. Maybe I'll buy the manometer and have my son test it while I'm out. So you can count on a thread bump in some weeks...

Is this the right port to plug either side of? UAOS to intake behind throttle body? And if so... Could this be correct? 0.50 in / H2O

Quotes source post: 17076387

Yes, that is correct but you should also plug the purge vent line. The 0.50inh20 is not a plausible value, it indicates a leak somewhere in the purge line/valve or in the crankcase.

Went back to post #75 and disco�d/plugged purge vent. Reversed ports (duh) and got same reading. Crap. Could it be one way check valve to manifold?

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With the vent line plugged and the UAOS/AOS line plugged, all blow-by should be exiting the .110 orifice in the oil cap and a plausible reading will be around 4inh20 at idle. A low reading indicates the blow-by is going out somewhere besides the .110 orifice. ( a leak in the oil pipe, AOS crossover tube, AOS blow-off valve (996.1 only), a rubber cam plug ect) A high reading will indicate excessive blow-by due to bad ring seal.

Thanks Skip.

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No problem !!! Hope you find the leak easily and get some good blow-by numbers There is so much good data in the 996 community that can be had by doing this simple test..

Finally have some data to post. However, the value seems lower than the discussion expects, but is higher than the lowest implausible value mentioned. Here goes... First, the zero of the cheap manometer is -0.24 with the engine off Manometer zero with engine off The crankcase vacuum reading is -5.42. Adding the zero makes this value -5.18. I believe this is an OK value. 95k mi on engine, 20k mi on AOS, 5W40 oil, engine at op temp, at idle Here is the value after disconnecting the AOS at the throttle body and the vent line at the quick disconnect and plugging all 4. The value is 2.38 plus the zero offset make the real value 2.62. Blow-by. 95k mi, 5W40 oil, engine at temp, at idle Extrapolating from the table above, the blow-by on this engine is 11.3 l/m. Seems like its either really good, or I have an additional leak. Need some professional opinions... The primary problem I had making this measurement was the position of the fitting in the cap. The position above kept me from being able to seal the cap. If you are going to make a cap for this, I would recommend you put the fittings and port hole like this:

When analyzing blow-by values you can always believe HIGH numbers, be cause the only way increased pressure can only be caused by increased blow-by, but a lower than expected value is to be taken at first with a grain of salt. Your 11.3 L/M value on blow-by is remarkable, but not impossible. Therefore I would do a little more investigation before calling it good. If yours is a 996.1 I would inspect the "bellows" of the AOS for oiliness, it's a common overlooked place a small leak can start and still be so small it doesn't effect A/F ration enough to set a code. Also the fill tube is common, and here is a diagram of some other places a small leak can be. Inspect for any signs of "oil mist" in those areas...

This is a 996.2 (2002), but I expect the same rules apply. Look for small leaks at all these connections. One observation was that the blow-by value seemed to 'hunt', varying by +/-0.2. The idle on this car is quite stable. Knock wood, it's never thrown a code. I don't recall if the AOS/Crankcase vacuum was hunting. If the vacuum side doesn't vary and the pressure side hunts, that certainly could indicate a leak as the vacuum could be pulling some small cracks together for a better seal and the pressure will push them open. The plan is to look at these connections over the next weeks and measure again as I get into my Ohlins installation. Stay tuned! (sorry, I seem to be the slowest working enthusiast on the boards)

You are definitely NOT the slowest working enthusiast on the board .....

Dear Porschetech 3, I just completed a theoretical study of the venting of my 1958 Velocette Venom m/c, and find an excellent match with your test result on your Porsche @ 4600 rpm full load. Could you perhaps help with more up-to-date info about your water manometer, working principles and assorted charts, etc... ? And tell me where I can fetch one, eventually ? Regards, michel6244 Brussels Belgium

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Hi from USA !! Manometers have been around for ages, I have an analog dial type from FoMoCo that was a special tool used to calibrate "variable venturii carburetors" of the 70's era right before EFI became the norm. The VV Carb was a technically sophisticated but mechanically simple carb that at the time only a few techs could overhaul and tune one. Had a big rubber diaphragm that failed often (sound familiar?)... A manometer is a scientific instrument used to measure gas or liquid pressure . Open manometers measure gas or liquid pressure relative to atmospheric pressure. A closed manometer measures pressure differential between two pressures. The pressures are of liquid columns of water, oil, blood, mercury ect. For UAOS/AOS tests we use "inches of water" inH2o in a digital open manometer. 1 psi (pound per square inch) = 27.7 inh20 (inches of water column) so you can see how sensitive it is... Digital Manometers can be found really inexpensively nowadays, for our use just be sure to get one with a range of 0 to 2-3 psi or 0 to 50-80 inh20 in the open (single port type)

Ok here is how to do (and NOT) do the blow by test for you visual learners like me Thanks for all the help and guidance Skip! How to perform a BLOW-BY TEST on a Porsche You Tube

This is definitely NOT what you want to see, but it is what it is, and the reason we do these tests, to find out the truth... For clarity/comparison my engine has 140k not 104k, and the test was 4 inwc at idle .110 orifice ( 14LPM) and 8 inwc full throttle .221 orifice( 80 LPM) and I would consider it average, this engine is 128k and the test showed 37 inwc at idle .110 orifice ( 42 LPM) and 35 inwc full throttle .221 orifice ( 170 LPM) ..... I thought the little glove trick was funny, it made for an entertaining and informative video !! Thanks for sharing !!

Always glad to entertain 🤦‍♂️😆

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Entertaining or not thanks for posting this video and the other ones you made! I'm a visual learner and following written directions leaves a bit too much to imagination sometimes, resulting in major code brown if something goes south. What's your course of action now that you know the blow by numbers?

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Same here with visual over written. Sometimes �plug it�, for example, isn�t quite as descriptive as it needs to be 😆 Next will be taking it to the track this weekend then going over the fuel trim values again now that the breather hose is fixed. Then installing a deep sump and checking the cylinders completely while that�s off.

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NO !!! I would not be tracking that car with that much blow-by......your asking for trouble......If you want to put some miles on it to see if the fuel trims being corrected will drop the blow-by numbers.... I suggest doing that by just cruising and maybe a full throttle for a couple of seconds at a time...... Make sure that engine is healthy before taking it to the Track....( good blow-by numbers----good oil pressure -----no metal debris)

2003 996 w/ 212k miles *Note I'm at 6000' elevation so not sure if lower air density affects crankcase vacuum and pressure? EDIT - here�s my official re-do of this after plugging the purge valve. I was getting inconsistent jumpy values without plugging it AOS test: -5.65 in H2O Blow-by test: +6.45 in H2O. It took a little bit to settle into this but ended up being consistent somewhere between 6.30 and 6.60. Without plugging the purge valve it started out at +3.52 in H2O but then dropped to +1.80 in H2O after a couple minutes. These numbers are at idle, engine temp at 180 degrees. AOS vacuum: Blow-by

That equates to 18.25 Liters per minute of blow-by...not to bad for 212k miles.... As you can see in the video the 128k mile Cayman has 42 LPM at idle...WAY too much...

Thanks. I was kinda surprised! Two questions: 1) Are high blow-by values a symptom of bore scoring? 2) Are my squirrelly numbers with the purge valve attached indicative of a problem with the valve, or just simply that it activated while I was testing? What are the symptoms of a bad purge valve? Thanks for the great idea for the test. I�ll be doing this on a regular basis to monitor the engine�s health as I put on more miles.

Quotes source post: 18766281

1. Yes, bore scoring will cause high blow-by values..... 2. I think your purge valve was purging while you were testing...there is an audible clicking sound also from the valve while purging, but always better to plug it just in case.. Symptoms of a bad purge valve is usually very hard start after refueling........

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Good stuff thanks!

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No Problem,,..Thanks for sharing your data.....I wish more people would do the simple test I designed, Like I said in the OP, blow-by is the best kept secret of top engine builders.. All manufacturers and engine builders strive for the lowest blow-by numbers / best ring seal by testing different ring packs, cylinder surface finish, ect.. But testing and getting a high blow-by numbers means the rings/cylinders are not sealing well for some reason, and there is torque loss, oil consumption, increased emissions, increased burden on the crankcase vent system ect.. not a healthy environment.. Rule of thumb is that when the blow-by numbers double from new, it is time to rebuild/repair...our m96 engine is the easiest to do this test on...

Data collected from several cars used as trend dat collectors indicates that during the period of stage 2- stage 3 bore scoring that blow by values can actually be stock, or better than stock numbers. During this phase oil consumption also changes, as well as the audible indicators of scoring. During this period just enough oil is making it past the rings to artificially enhance sealing, thereby reducing blow by. At this stage engine roughness values changed, and so did the knock sensor data. These things are being impacted by oil entering the combustion chambers, boosting cranking compression a bit. Just enough oil in the chamber seals the rings better, and the engine will hardly show any signs of this. It won't really even smoke, since the cats cancel a lot of that out until advanced bore scoring is reached. These are some of the reasons that engines with bore scoring are often described by their owners as "running great". It also seriously confuses diagnosticians that don't understand the correlation between these things and symptoms. This is also why engines that have stage 2- stage 3 bore scoring can pass a leak down test and a compression test with flying colors. We've trained the Certified Installers (and some others) not to perform these basic tests that are usually the "go to" with other engines, since they are a waste of time and resources. When I first came here I reviewed all the bore scoring videos and this didn't;t make much sense to me at that time. Almost 18 months later I see these tests being done, indicating nothing, and engines later having scoring clearly found with a visual bore scope inspection through the oil sump. It only took a few experiences with this to learn how things occur, and why we see the same botched tests over and over again. I have a ticket in the system right now that has compression test figures included, and they are better on the cylinders that were later found to have scoring. When I was told that better than normal compression test values were an indicator of scoring, I really started to pay attention.

Judd what is the nominal blow-by value of your engines after break-in and at what value do you consider a problem?

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There's no standard value for this, since we use a variety of different rings, and other variables. Some engines use gapless rings, others use conventional, and others have gas ported top rings. Some have gapless and gas ported. It is all in what the engine called for, and what the purchaser may have upgraded to. The differences between piston manufacturers also plays into it, especially since some engines see close to, or even over 13:1 static CR. I'll ask Jake for some basic values for the engines with the most conventional rings, although we seldom use them. The one thing I've experienced that impacts the values most, regardless of components is over fueling, which always creates blow by, no matter what. You can't even perform the test if the engine has been fuel rich. If the engine is rich, correct that issue, drive the vehicle, let things normalize and then test. If it goes super rich that can take a couple thousand miles. When I've seen Jake performing blow by tests on new engines he always did the tests by driving the car, and a lot of attention was paid to what the values were on the dyno and how they overlaid the torque curve with the AOS connected and also with the AOS out of the equation. I can't honestly think of a time when I saw him do these tests at idle speed, but I really didn't pay a lot of attention.

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Right, ..... All engines wear out or have issues at times and I use this test to see how well they match to the expected values...an increase in blow-by is expected over time or if issues arise.. The test is very very accurate and at idle it shows the worst percentage wise, where as there is more blow-by under full throttle, but percentage wise is less compared to the air that is consumed..

When I asked Jake why he didn't use idle values for the test he said "because the car isn't driven at idle" So I left it at that a few minutes ago.

I like to see them both..

I thought I would update this thread with some new data points and a chart to consolidate the data since we have a few data points now and more being gathered... Owen just sent me his data he has been collecting on his FSI engine as it was breaking-in... at 20k miles it was 29,8LPM @ idle ,at 24k miles it was 14.785LPM@ idle, and at 26.6k miles it was down to 12.75LPM@ idle, showing it takes almost 30k to full break-in the rings/Nikasil liners... Blow-by Data Owner..................... LPM@idle .................H2O@idle................ LPM@WOT ..............H2O@WOT............... Miles... ::notes Porschetech3 .........14.5............................ 4.0 .............................81 .............................8.0 ............................140K ........runs good on and off the Track jdbornem .................12.25.......................... 3.12.................................................................... ............................ 100k JTT ...........................12.8............................ 3.26 ........................................................................ ..........................80k Blacksquid ..............15.25 .........................4.49 ........................................................................ ...........................34k golock911 ................11.3 ..........................2.62 ........................................................................ ............................95k TTGator ...................42.0 .........................37.0 ..........................170 ............................35.0............................. 128k........ bore-score on #6 cyl MyFavorite996 .......18.25........................ 6.45.................................................................... ............................... 212k Owen .......................29.8 ........................................................................ ................................................................20k..... ..... FSI on break-in Owen ......................14.75............................................. ........................................................................ .................. 24k.......... FSI on break-in Owen ......................12.5 ........................................................................ ..............................................................26.6k ..........FSI on break-in

I ran another blow by test, but again got wonky results (way low). So I removed the purge valve and confirmed its operation, and cleaned it out. Reinstalled and did a smoke test. Found another leak around the brake booster and sealed it up with some sealing tape for time being. No other leaks noted. Went out again this evening, go engine fully warmed up and ran test again. I�m running an UAOS, so plugged off the back side of the UAOS diaphragm, line into intake from UAOS, disconnected the purge valve at the quick release and plugged both ends of it. 1.29�H2O with .110 hole open. I then removed plugs and hooked everything back up and tried a straight AOS test, putting the plug back into the hole in cap...2.50�H2O (which seems way low, but I�ve never tested since installing UAOS...maybe it reads different?) I�m clearly forgetting/missing something. Likely really obvious, but hoping to get some direction where to look. Thanks, Joe

Low readings are what you WANT to see !!!...( see caveat below) A high negative Inwc reading when doing the AOS test or a high positive Inwc reading when doing the blow-by test is ALWAYS BAD !!! A low negative Inwc reading when doing AOS tests or a low positive Inwc reading when doing blow-by tests is GOOD ...BUT ONLY if it is confirmed that there is no leaks !!!

The UAOS normaly reads 1" wc lower than the stock factory AOS system.....lower is what you want.... I would suggest doing the smoke to again just to quantify there is no leaks....If none, then be happy that the readings are LOW...

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Thanks Skip! I�m suspicious, as number are lower than they were 4 yrs ago. Seems odd for numbers to improve with age...maybe those magic beans were real! I�ll smoke it again. I smoked through throttle body. Is there a better source point?

Quotes source post: 19374788

Try sealing off the throttle body and smoking through the oil filler tube...

So, I have been doing blow-by testing since the 80's when developing my World Record holding 2.0 liter Turbo T-88 Series using this method...It is interesting that not that many people do this type of testing but this recent video by Lake Speed Jr. and Wagner Competition showing the complete testing of the Total Seal gapless second ring vs the traditional second ring... I was surprised by Lakes comment that "they" don't normally do these types of tests. With him being involved with Total Seal Rings I would have assumed these type test have been done exhaustively, apparently that's not the case as in this video they say this is the "best" test they have ever done.. This test does show that the Gapless ring on this High Powered Diesel engine does reduce the blow-by from 9 CFM ( 254.8 LPM) to 5.75 CFM ( 162.7 LPM) , so drop of almost 100 LPM in blow-by !! That's pretty good ... Other than evaluating different rings and cylinder finish, the blow-by value can be used to tell when is time for a rebuild... Rule of thumb is when the blow-by doubles from where it was as a new fully broke-in engine, , it is time for a rebuild... Through much testing with AIM data system on the Track, and in the developement of the UAOS SYstem, I have found the blow-by on the M96 engine plays a very important role in the usable oil level in the Sump...The lower the blow-by and the more the blow-by can be controlled, the more oil can be added to the "Integrated Dry Sump" without any harmfull side effects and the positive effect are MUCH better oil pressure stability... The blow-by test equipment used in the video is a J-Tech Product that costs $4K just for the Sensor and $7K for the complete system with display...The test procedure I show in this thread can duplicate the exact same results from about $50 worth of equipment. The key to the procedure/accuracy is the conversion chart that I made using the simple formula In my younger days I was all about Horsepower, doing any and everything I could to gain a few extra Ponys, but in my old age I am all about longevity, and getting the most mile per $ out of an engine and making it Bulletproof... blow-by test in CFM... to convert to LPM multiply CFM by 28.31 = LPM Here is the full video for your entertainment .. You Tube

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No Need for a Dyno and $7K worth of blow-by data equipment. With 1 mile of straight road and the $50 worth of equipment listed and the Converstion Chart, you can get the exact same Blow-by Data .. It's all about the "Science" and not the cost of the equipment...I have been doing it for decades... The Science I use to perform this on the M96 engines is actually a modified version of the ancient Volvo-Penta Marine Technical Blow-by Procedure..I just customized it for the M96 specifically and modernize it with a digital Manometer...

Very interesting. You believe in science then? I like it.

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Yes, I do believe in Science, but I also believe in the Supernatural World and that they overlap, you can believe in both..The Porsche Gods approve this message...

Another data point� Got around to doing this test today after a fresh oil change and 40 mile twistys run. 996.2 C4S 3.6L with 241.8K original miles. Initial vacuum reading at idle with AOS and vent valve connected = max vacuum of 5.33 inH2O Pressure at idle with AOS and vent valve plugged, 0.110� hole open, 0.221� hole plugged = 1.96 inH2O = 10 L/min = 0.35 CFM Pressure up to 5K rpm with AOS and vent valve plugged, 0.221� hole open, 0.110� hole plugged = 5.91 inH2O max with manometer on record = 70 L/min = 2.47 CFM Forgot to take picture of this one.

@cboxell Excellent results !!! Your cylinders/rings are still doing very well at 241k miles....Thank you for the data point. It's such an easy and important test to do, agree?

I did the test this weekend on my 128k miles 99 c2 M96.01 3.4l manual after an oil change (to 10W60). Getting the AOS hose off and plugging it and the fitting on the divider pipe proved to be the hardest and most time consuming part. Idle test was inconclusive as the manometer only showed 0.2" water column. I suspect the AOS hose wasn't properly plugged or I must plug the charcoal Canister vent hose too. If not that, then I have a vacuum leak somewhere else... After that (no change to AOS plug) I did a WOT run to redline in 1st yielding 9.8" water column (90 l/min) and then another in 1st and 2nd gear WOT to redline yielding 14.6" H2O equals 107 l/min

@hardtailer Thanks for the data !! Yes I think you have a slight vacuum leak or purge valve leaking ...also either one of those can cause a lean condition that can make the fuel trims go richer and effect ring seal... Check that the fuel trims are not on the " rich side" ...that can cause the rings to loose seal and increased blow-by.. That said 14.6 inh2o is not that bad, I have seen brand new Slakker and FSI engines that were higher than that (19-24)before the rings have fully seated...

Hey Porschetech3, I�m assuming the measured values you obtained in your first post (80 LPM @ WOT, 14.5 LPM @ idle) pertain only to the M96 engine, right? I am interested in doing blow-by tests on other cars, and so I assume that I�ll need to acquire my own baseline numbers for each engine�. What about manometer vacuum readings for testing the AOS? If I were testing a BMW�s air-oil separator, could I conclude that it�s operating normally if I see a vacuum reading of 5.0 inH2O? Or is this value also specific to this engine� Thanks!

@996love The 4-6 inh20 ( 3-5inh20 for UAOS ) AOS health test is for M96/7 cars only...I don't have any idea what is normal for BMW, other models can be considerably different..You can't use our specs on other brands, you can't even use our specs on other models Porsche's .. Application Equation for Typical Blow-by @- WOT Suggesting Problem/Rebuild M96/7 production motor .005 x Peak Tq (ft lbs) = CFM x 28.31= LPM ..up to... .015 x Peak Tq (ft lbs) = CFM x 28.31 = LPM For example, if you have a modern production vehicle (naturally aspirated, turbocharged, most anything) which has an peak torque of 300 ft lbs, it will likely produce about 1.5 CFM (42.4 LPM ) of blow-by (300 x .005 = 1.5 ). You would consider the blow-by high, indicating the rings may be bad or cylinders scored if the blow-by was over 4.5 CFM (127.3 LPM ) ...300 x .015 = 4.5 CFM x 28.31 = 127.3 LPM CFM X 28.31=LPM- Liters per Minute PS :: The blow-by has a HUGE impact on the M96/7 engines due to the Integrated Dry Sump system, and is the biggest factor in determining the maximum oil levels that can be ran, which is extremely important in high-G maneuvers...

Holy cow, thank you so much for teaching me the formula, as well as providing an example. That was, yet again, a wonderfully informative post! I hope you�re doing well.

Another great post by PT3. I built almost the exact same digital manometer and have used it on all my cars. As mentioned the vacuum reading will vary depending on the specific engine. As a general rule of thumb direct injection engines like the 9A1 run much higher vacuum. Many OEMs also doubled the vacuum after the fact from ~15� to ~30� of water to improve ring seal and reduce fuel dilution. This is less of an issue with port injected engines like M9x. This requires a new AOS and usually an ECU update/flash.

@silver_tt Glad you found it usefull !! Remember guys, there are TWO important Manometer Tests for our cars.....(1)The AOS Health Manometer Test , and (2) the Engine Health /Blow-by Manometer Test .... Both are extremely valuable on or cars for Maximum Performance..

So here are numbers from my 987.1 rebuilt to 3.8L. Engine has maybe 3000 miles since rebuild. Fully warmed up today at idle. 1. AOS intact and test cap ports plugged I read -5.9 in H2O. 2. Removed hose and capped intake openings and AOS opening. Opened the .110 hole in test cap. Monometer read +1.87 in H2O. chart converts that to 38 lpm. Divide by 4 is 9.5 lpm which converts to 2.5 cfm. Seems that last number is OK. Any comment on the system operating number?

@jesseellington thanks for the data point !! The values for AOS health and blow-by at idle look good .. If your Manometer has a "Min/MAX ' function , you can plug the .110 oriffice and open the .221 orifice and go for a WOT run and get the blow-by value at peak torque...

Hi @Porschetech3 ! Thanks so much for putting this test together! I'm running your UAOS Track Edition (yes!) on a 2006 Cayman S w/ 53K on the clock. Manometer: HT-1890 I ran the idle test (.110 orifice c/o drill bit #35) on a warm engine and am finding that my inH20 readings (both vacuum and blow-by) are fluctuating. Vacuum (orifice plugged, UAOS to intake connected, manometer minus port): -4 ... -3.87 ... -3.78 ... -3.88 Blow-by (orifice open, UAOS plugged + intake plugged, manometer plus port): 2.20 ... 2.31 ... 2.14 ... 2.27 I read through the posts (might have missed it) but no one else is reporting this so I assume this is unexpected. Is this indicative of a leak somewhere (possibly the other brittle original AOS lines)? I'd be grateful for your thoughts!

@dxrohanx those number are right where you want them !!!! Thanks for posting the data point .. Digital meters are highly accurate and will pick up even the slightest variations quickly ( no smoothing/average) ... Yours is nothing to worry about it is just picking up the fluctuations of the fuel trims going from rich/lean and moving the rpm slightly..

Cylinder bore/ring seal ( blow-by) was pretty much settled at one time, but the constant push for improving fuel mileage and efficiency/power and the ever changing technologies and engineering has lead to constant changes suck as low tension rings, thinner rings, changes in ring materials, changes in cylinder materials , cylinder finish, cylinder honing processes, and even break-in procedures...The apple cart has been constantly upset and the challenge of keeping the ring seal ( blow-by) to a minimum has been a constant battle..... Reducing ring tension and friction by the new technologies is good for efficiency and power but is a lot more challenging to also keep the ring seal (blow-by) as low as possible.. Some small inconsistencies even in new production engines have always existed due to manufacturing tolerances, and even in specialized rebuilt engine there will be variances due to clearances and break-in procedures in general.. But the constant quest to minimize blow-by and improve ring seal still goes on every day....The lower the blow-by the more torque/power and efficiency the engine will have.. Here is a new ring coating by SouthWest Institue that will be available probably in the next year from Total Seal in this video that shows an improvement of about 28 LPM of blow-by on an engine that had a total of about 84 LPM before the new rings .. You Tube Here is another video from Total Seal showing a 1000hp Diesel that had about 252 LPM blow-by that was reduced to 154 LPM of blow-by by changing the second rind to a gapless ring... You Tube Total Seal has a lot of good content and videos on ring seal technology/ blow-by..,, Of course they do because that is the companies livelihood...I will post more of them from time to time here. These blow-by results can be gotten using the method described here in this thread on our engines, no need for the 7K equipment shown a couple of videos here or any other equipment.

Yup, full ring seal has always been a design goal. Problem is, whats the definition of full ring seal...? Gapless rings seem to do the best, but add additional problems..? Low tension rings with sophisticated coating do well also, till the cyl/ring/piston wear sets in and further lowers ring tension to unacceptable levels deteriorating cyl seal way before it should imo. Its all a compromise. The new diesel trucks seem to have gotten ring seal/durability right for the most part for low rpm engines that lasts for not uncommonly 500,000+ + miles. Many well cared for(not raced) Mezgers seem to last for a good few hundred thousand miles also with their old nik-sil technology even with forced induction. Something very few na (advanced hypereutectic loco-sil cyl tech ?) m96 can claim if any....

Here is another entertaining video from Total Seal Rings on the new variable coated rings.... Remember guys, blow-by is EXTREMELY important on the M96 engine due to the Integrated Dry Sump, flat six design.. You Tube

Why is this better than a compression and/or leak down test? This test assumes that there are 0 vacuum leaks, the AOS is in perfect condition, and that there are no other factors that would be impacting the crankcase vacuum. Worse, these factors pull the crankcase vacuum in opposing directions leading one to think the engine is healthy when it is not�e.g. a failing AOS increases crankcase vacuum while present blow-by brings the crankcase vacuum back to the nominal value. Compression and leak down tests isolate what we're really caring about when it comes to engine health: the cylinders holding pressure so that the most force possible is imparted onto the piston by the expanding gas.

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My impression isn't that it is better, just that it is different. Speaking as a non-professional DIY'er. I can actually do this one. I don't have the equipment, nor the inclination to lift the car, remove the wheels, trying to get to the spark plugs for a compression/leak down test. At least not as a quick/easy engine health test. And to my understanding, yes, if your car is broken in another way, the blow-by data may not be reliable, but I don't think that's too surprising. Although a vacuum leak isn't that hard to identify through a code, rough idle, or even a smoke test. And within the very first post on this thread, it was already said that testing the AOS can, and should, also be done with the oil cap hole sealed, which should result in a vacuum reading. That should be done first, and if the AOS is good, then the blow-by test can be done. Further, people have posted pretty typical values, so if someone gets a number outside of those (even too low), I wouldn't take it to mean the engine is perfect, but that more investigation is needed. Last, I think the most value here doesn't come from absolute measurements, but from tracking measurements on the same car over time. If my blow-by drifts up over time, are my rings not sealing? Do I have bore scoring? If my blow-by goes down, do I have a vacuum leak? Did my AOS fail? etc.?

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I suppose that's my point�it's a vague test to the point where I don't see why this would be part of someone's troubleshooting routine. If someone does this test because they suspect something is wrong with the engine, the test will say, "yes, something is wrong the engine" and you'll end up getting your hands dirty doing tests that give you specific information about the engine, anyway.

@lorkprenn you have missed the purpose of this test, and made a few wrong assumptions... The purpose of the test is to determine the degree of engine health...by measuring the blow-by, The Blow-By value is extremely important on the M96 for maximum reliability when asking for maximum performance like high speed, high G force, high temperature cornering... Compression tests, and Leak-Down test are Static Tests, the Blow-by Test is Dynamic....in general, Dynamic Tests are better than Static Tests and give more particular info in exacting circumstances... For example a compression test can miss a bore scored cylinder ( due to excess oil can seal the compression) , and also miss a broken valve spring that seals compression at cranking speeds, but the valve floats at running speed... Also, neither Static test will reveal high speed "ring flutter"....but a Dynamic Blow-By Test will reveal this... Compression Tests and Leak-Down Test have their place and purpose, but are for more simple less complicated diagnostics..( such as hard failures..ie. broken valves, extremely worn parts) And yes, the Blow-By Test is actually easier/quicker test to perform than either Compression test or Leak-Down test... That said, the Blow-by test on the M96 is extremely important for oil control from the crankcase ventilation system...During high speed cornering the oil will shift to one side head and will sling off the timing chains/gears directly towards the ventilation ports...The more blow-by volume/flow the more oil will be carried into the ventilation system and overload the factory AOS, and the reason I developed and patented the UAOS System. It can handle the excess flow and more oil to the point you can even run a higher oil level to prevent oil starvation... It is a very complex subject and why there are thousands of posts on it yet still difficult for some to wrap their head around it...

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Great explanation. Everyone should copy and paste for the next time they scratch their heads on what is happening internally and why the factory AOS struggles.

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If the test says that there's blow-by, what's the next test to do to figure out which cylinder(s) it is?

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That question need to be much more specific to get an accurate simple answer that is without reproach.... That is like asking an Astrophysicist why the Sun comes up .. I will say that ALL engines have Blow-By........ None are perfect and what this test does is measure the degree of imperfection...Those degrees of imperfection are extremely important when it comes to oil control... If you are genuinely curious go back and read all my posts in this thread and if your still have questions ask a more specific question..

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Would I skew the measurements by using extra-long vacuum tubing so that my digital manometer is inside the cabin while going for a WOT run? Let�s assume I don�t accidentally pinch the tubing while doing so.

I tried a long vacuum hose on mine the first time before I realized my manometer had a min/max on it that would store the values, and there was a good bit in of delay in the values and I didn't trust them.....Then I realized the min/max and just turned the meter on and laid it down besides the air box and went for a drive and came back and checked the MAX reading...

Okay. I want to avoid having the manometer fly around in the engine compartment, so I think I�ll use some duct tape for peace of mind.

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There is always some blow by, on every engine. The amount is what we are trying to detirmine with these tests. As excess blow by on a flat 6 can translate into poor oil control. Just a guess, as PT3 is the 996 blow by expert.... but A compression test and a leak down test might help shed some light on excess blow by. Now keep in mind we are not looking for a failed cylinder here (hopefully) just cyls that are not sealing as good as they should. Old Baseline tests from new after break in would be great for comparisons. I always do a compression test immediately after rebuild and after break in to see how good rings are sealing and give me a baseline for any future problems. Probably will add these blow by test to my post rebuild data also.... So a small variance( a few % ?) in a compression test or leak down test, can be substantially higher/more at wot cylinder pressures. This could/probably will, translate to higher blow by in that cyl. Also, excess blow by could be in all the cylinders not just 1, so a baseline test comparison might help show this problem. At least thats my thoughts on this. Maybe PT3 will chime in here and correct me..? jmho

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Right !! Securing the manometer is a good idea..My Car has a Custom intake and heat shield so less worry about it flying around, just tucked it in.. No need to correct you, you have a good grasp on the engine physics/functions... I do some Private Consulting and some Expert Witness Reports/Testimony on a few Litigation's .. Right now I'm working with a client in Europe with a fresh 700 miles M96 rebuild with Nikasil that has 90 inH2O ( 300 Liters per Min) blow-by.which is WAY WAY too much, especially for a fresh engine....... I've also Consulted with Slacker to help get their blow-by numbers lowered........I'm trying to educate the owners and Top Engine Builders on how important the blow-by numbers are.....

The work you did with us was a game changer. Generally, we see around +12 (0.110 hole at idle) when we first build an engine. It seems like +6 is about where we stop seeing significant smoke at startup. We've been experimenting with BR50 since BR40 tends to break down pretty quickly. With BR40, we start seeing oil pressure decay from 55-60 psi at 3000 rpm during our first 30-minute break-in period to 40-45 psi during our second. After determining it wasn’t an issue with our engines, we experimented with BR50, and oil pressure held solid at 55 psi. However, we were really struggling to get to +6 with an engine today. So, we switched back to BR40, and 30 minutes later, we had it down to +2 (at 44 psi of oil pressure).

Good work Slakker with blow-by numbers like that and UAOS-T owners can run 1.5-2.0 quarts oil over full with confidence....

A very good thread to resurrect. Thanks Skip.

118k miles C4S '04 Blow-by max of 2.02 inchH2O = 40 LPM/4 = 10 LPM at idle (warn engine, 0.110 orifice, blocked purge valve) AOS = -5 to -6.xx I'll be ordering the UAOS soon. Just trying to be ok with the price tag

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Excellent Blow-by Test Results ......It means your engine is in very good health and I know you plan to keep it that way !!! Just a heads up on UAOS price, The UAOS has not had a price increase post Covid, but all the materials, supplies, and labor have gone up substantially..and I have found ways through buying in volume and production efficiency to keep from a price increase... But the time is due for a price increase shortly, but I will be doing a Combo Discount for UIDS/UAOS as the Patent for UIDS has been accepted by the USPTO and will be issued in ~ 3 months, so I will be doing a Celebration Discount for the UIDS/UAOS untill the Patent issues !!

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BOGO discount,,, thats cool man...

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The UIDS/UAOS is such a great Combo like Peanut Butter & Jelly or Chocolate & Peanut Butter ( Recesses Cup ) I figure why not ???

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LOL, you know i was just kidding. You probably couldn't make enough of them to keep them in stock with that BOGO sale.

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Yea I know.....you would even buy one !!!! lol....

I'd buy another one if I found a '02 Targa with bore scoring(roller with a core)... I'd put it on the FSI R-series engine I'd have built for it.

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Targa's are so cool and rare......but keep your eyes peeled and $$ ready one will pop up !!!!

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FWIW- The UAOS/TD price is just a normal number - especially for what UAOS/TD does for your engine. Just accept it and buy it. PT3 does not add sales tax, so there is something.... Some cities and states add up to 16.5% tax, be thankful. I believe PT3 has kept the price as reasonable as possible and still make a profit of some kind. Afterall, what costs the same today as it did 6 months or 1 year ago? Not much. YMMV

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I was quite surprise by the blow by result. I suppose was expecting the worse. I mean it does drive great 😅 congratulation on the patent award! I�ll be heading to LN website to purchase the UAOS as they have military discount 😬

Haven’t got to blow-by yet but, did get a manometer reading on just the AOS. ‘03 C4S w/115K miles. Have had the car since April and am trying to prioritize systems and develop a proactive, elective maintenance plan. This seems a bit low based on reading various threads but, is an initial data point. Realized I must have been connected to the wrong input.

Pulled the trigger from Charles� website. I was misinformed about LN. They do not offer the discount.

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What do you mean ?? You bought a UIDS/UAOS Combo from LN ?? I haven't set up the discount yet .....

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I was referring to military discount for LN website. They do not offer it for your UAOS as they obviously do not make it.

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Oh ok,,, I see...Well thank you for your Service !!...My Dad fought in 2 World Wars...He enlisted in the Navy at 16 years old for WWII , after that he finished High School then re-enlisted for the Korean War....lol....Then spent the next 33 years working for US Steel I wish I had something appropriate to send you ...I'll think on it ..

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to your badass father and as for me --- i don't need anything. you making a great product for our beloved 996 is more than enough! thank you.

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‘04 C4S manual, just hit 99k miles. AOS test Blow-by I had difficulty getting a consistent reading on the blow-by test. I had the AOS tube (and purge valve) and intake port capped, a .110 open hole on the test cap, car at operating temperature, and would often get values around -2.31 inH2O. Before the photo reading, I had turned off the A/C compressor to keep the idle lower and it went to -1.68, and with the compressor re-engaged (and idle stabilized) it hit -4.93 then crept to -4.54 and so on. The AOS readings were stable. I must’ve erred a bit on the blow-by test as I used a dense neoprene block on the intake port as I didn’t have silicone plugs large enough to fit.

@Deserion 5 inh20 ( 16 LPM ) at idle is not terrible, in fact not too bad...The worst I have seen is 37 inh20 (44 LPM ) at idle and it was not ticking or smoking ,but we did find a good bit of Bore-Scoring on #6 Piston that was causing the excessive blow-by ...

@Porschetech3 My goal was to ensure the engine could handle the UAOS +2qt. Today I should be able to get a more precise test as I’ll have a better plug for the AOS port on the intake. While I’m not entirely certain that was the cause of the numbers decreasing it’s best to eliminate any potential for variability. That said, how (un)common is it for the number to start higher then drop off? Also, is there a graph for converting inH2O to LPM? Earlier posts mention it but I’m unable to see any. Thanks

@Deserion Post #1 has the Conversion Chart for InH2O to LPM at WOT .....When using for Idle Test Divide the LPM number by 4 ... Its not unusual for the reading to drift .5 to 1.0 inH20 as the RPM or Rich/Lean adjustments take place.......just give it a bit to stabilize and/or use the average..

@Porschetech3 For whatever reason I was looking for a graphic chart and not an attachment. D’oh! Sorry about that.

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No Problem !!

@Porschetech3 I ran the test again today but with the purge valve and line plugged as well. It certainly allowed for a more stable reading range than before. The values did bounce around a little in the .5-1 range you mentioned before. Sorry to keep pestering you on this, I want to make sure I’m running the test as best I can. With the A/C compressor off, the reading is around -1.75inH2O, and with it engaged around -4.8inH2O. Is the additional load from the compressor (though with idle stabilized) enough to skew the readings? I tried to run through the thread and search results to determine if this should be done with the A/C off or if it doesn’t particularly matter.

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This test is extremely accurate and uses very very light pressures ( 1 psi = 28 inH2O ) so yes, any variation of RPM,load, vacuum leak ect. will skew the test value...That said, your value is not grossly out of range ...( this is a good thing) Also please pay attention to which port on the Manometer you hook your hose to on the two port Manometer.......When testing Blow-by you should see a + ( positive value) and when testing the AOS function you should see a - ( negative value) ....Using the correct port keeps down confusion and false assumptions...

For anyone wanting to create the gear to do this test, I found this oil cap on eBay for $11.48 with free shipping. Engine Oil Filler Cap for Porsche 911 1999-2005 Boxster 1997-2004 Matte Yellow | eBay Although there are some pictures associated with the item that aren't associated with the actual item, the quality of the oil cap is outstanding and a fraction of the price of alternatives I was looking at. I also opted for the Risepro manometer, which comes with tubing and the barb fitting needed to connect to the oil cap. Amazon Amazon Although Risepro describes the barb fitting in the listing they don't disclose its full dimensions. The fitting is tightened with a 12mm wrench/socket, I drilled the hole with a 11/32" bit and got a sealed fit after warming the cap a little bit with a heat gun. I believe the proper size metric bit is 8mm. (I need to get a set of metric drill bits and quit screwing around). The Risepro manometer is of decent quality and its great to have the tubing and barb fitting included. This makes putting together your toolset a 5 minute job, max. Lastly, if you reading this far I'll also point out the precision .221 #2 drill bit hole is necessary only if you're doing the WOT test. I'm only doing the idle test so only the .110 hole is needed. I'm passing along links and have no relationship to the sellers I've included in this post.

Good work !!! @996.x Yes its crazy how easy it is to set up for this Test but yet how valuable the Test results can be.....

My reading was 4.16 @ 95,000 miles using the idle test. I stopped by my Indy’s place and compared crib notes. His Porsche parts source will sell him a genuine Porsche oil cap for $16, with free shipping. There is no question that the OEM oil cap is better and I would have spent the $5 had I been able to find it at that price. The flea bay unit is just good enough to do the test. Every Fall I will do a hibernation oil change and plan on doing this test with a UOA.

@996.x You have 14.5 Liters Per minute of Blow-by getting past the rings at idle on your 95k mile engine ,, not bad ... It's good to know exactly what the health of your engine is... This test, Oil Analysis, and Oil Pressure tests can give you such piece of mind and also get you a closer relationship with your car ...

Completely agree!

I've done the Blow-By test after AOS replacement to UAOS. It fluctuated around 2.3 inH2O - maximum value was ~2,7 (996.2 3.6; 2003 ~53k miles) - it gives up to 11,5 L/min so I'd say not bad at all!

Skip - When you get a minute, could you show us which vacuum sources to plug for the test with UAOS installed?

@hatchetf15 Sure .. I'll give very simple instructions ...Get this tapered rubber plug kit Amazon Amazon Break the connection between UAOS Accumulator and the Flow Regulator as shown in below pic... Install Tapered rubber plugs in the two open 19mm holes ... Install Manometer with Test cap and open .110 precision hole Start engine and observe value @tdz77 Very nice Test results !!! This shows your engine health is very good with little blow-by passing the rings . This means with UAOS you can run "oil overfill" safely ....when needed ......

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So if I have the UAOS installed on my car. I only need to plug these 2 holes at the accumulator? Possibly 2 other holes at the atmosphere vent valve ?

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I don't know what you are referring to on the atmosphere vent valve. maybe post a picture with highlights ?? And YES to your first question !! I know right !!!??!!

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I meant to say purge valve. Also noticed we have both been rennlist members for 15 years Skip!! Guess that makes us OLD..

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Old Yes !!!! ..15 Years on Rennlist is incredible with the Turnover Rate we have here !!! We get a new bunch of Novices every 5-7 years...... Purge Valve...ok......If you break the System where i showed, no need to worry about the purge valve, that is only if you break the system AT the Plenum on e-gas cars....

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Some of us novices have been here for at least 10 years.

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After 10 years I think you have graduated from the Novice Ranking...!!

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WOW !! New member coming off the bench swinging for the fence for a home-run ... @16plugs ..not to be rude ,but to be Technically accurate and factually... everything you just said is complete rubbish.. I'm happy to argue the technical merits with you civilly, and to show you where your errors of assumption are .. This Test Concept is probably older than you are and is still used by leading Ring manufactures today ( Total Seal,Perfect Circle ect.) .. The original Concept/Test was created by Volvo Penta Marine......I just modernized it after I Invented/Patented the UAOS System and discovered this Test Concept was easily modernized to work very well on the M96, since it was a very sealed System.. Just to quickly/simply negate some of your wrong assumptions :: 1: The AOS System has no effect on this Test as it is dissabled for the Test .. 2. The Intake Vaccum has no effect on this Test is it is disconnected and plugged for the Test... 3. Any Intake leaks have no effect, only leaks in the Crankcase ... 4. The AOS Health Test and Blow-by Engine health Test are two "Completely Different Tests", that just so happen to use the same equipment for the Modernized Blow-by Test ..I think your main problem is conflating the two... 5. The Compression Tests and Leak-Down Tests are Static or near Static Tests, therefor are not as accurate as the Blow-by Test, which is Dynamic.. 6.. Many people have great difficult in wrapping their head around either test, because they use the same equipment and similar procedures , but the vast complexities of what is actually being tested causes confusion and conflating of the two Completely different Tests.....ie.. these Tests can conceptually separate the Men from the Boys.. I'm happy to drill down further if need be ..

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Nicely explained my wise old experienced forum friend...

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Thanks my Internet Friend !! and I was Diplomatic, unlike the younger me .....

No one actually talks with that precision. I think it's AI generated.

Yeah, dont know what that was about.

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@golock911 A Chinese AI BOT attack on me/UAOS !!??!! I blew ChatGBT's mind the other day with a somewhat tricky simple clearance question.. After spitting out 3 pages of multiple solutions and then recognizing the solutions were wrong in the end it gave up and said 'Opps something has went wrong" ...LMAOOO

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Thanks Skip I will come back with results at some point.

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Thanks man , I appreciate the Data Point !!!

Have a 99 C2 and bought the items to do this test. To confirm, I will use 4 plugs - 2 to plug off the purge valve and 2 to plug off the AOS Line at the throttle body? Or just the AOS line and the Throttle body plugged off (using 2 plugs only)? Thanks in advance

1999 996.1 with 94,000KMs (~58,500 Miles) Blow by test, settled in around 2.45-2.5InH20 (Blocked off at Throttle Body). Car fully warmed up after ~40min drive. AOS Tested around 5.1-5.4InH20:

@Skeptikal12 Perfect Test results !!! The Engine Health and AOS Health are good .... You have 11 Liters Per Minute Blow-by at hot idle...This indicates the Fuel Trims and Ring seal are very good at hot idle meaning no wear or Bore-Scoring causing a lose of health ...@ 58K miles And the -5.34 inH20means the AOS in the good range of -4-6 inH20 for stock AOS value... Thanks for the Data Point ......

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Thanks for your expertise and knowledge. People like yourself make these forums a gem. All the best!

New data point! My 99 cable throttle 996 has 194,486 miles. It has remarkably little recent service based on the engine bay filth and condition of typical tune up components� all writing is long gone on coils and I don�t think an FI service has been done in some time. Cats look original and the exhaust welds are starting to rust though. I did have a vacuum leak I think but some driving seems to have cleared it up - the AOS tested poorly last week (-2in, may have been the purge valve) but it quit howling and now reads -5.1 to -5.25inH20. I read bang on +4inH20 at 680 to 720RPM idle, car hot. I have a UAOS in hand - with that installed, how much oil can I reasonably run in this thing for a bit of autox and a spirited drive? I�ll be on track in the future but have a ways to go before I spring for a UIDS� which will be the likely solution before it goes to the track regularly.

Thanks for the Data Point ..... The value of +4 inh2o at idle speed is 14.5 Liters per Minute of Blow-By.. With that value you should be able to run +1 quart overfull on the oil level after UAOS System is installed..... To go more you would need to verify the WOT Test Blow-By value... Also remember to use a 10w-60 high viscosity oil for Track Work ..

Both points duly noted! Thank you for the feedback, and for providing all this information and methodologies across such a wide range of diagnostics (not to mention product development!).

Good morning, sorry if this has been covered, I’ve searched through most of this thread and can’t confirm. But when using the manometer is the hose supposed to go on the positive side or the negative side? Here are my results with the hose plugged in on my positive side. For AOS test only I have not done blow by yet. 2001 996 86k miles Thank you

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For AOS test you want a vacuum reading or negative pressure. For blow-by testing you want a positive pressure reading. From your pic looks like your manometer automatically detected negative pressure even with hose on positive side as you got a great healthy AOS reading of -4.77

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Thank you for the reply, the confusing part is when I put it on the negative side. It gives me a positive number. That�s why I just wanted to confirm which port I should be using out of my instruments the positive or negative ports, assuming all these devices are built in the same manner, I see the majority of the hoses hooked up on the right side ports and all the other posts. so when doing the blow by test do I still use the positive port?

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Actually the vacuum reading on your meter is in inches of water column (inH2o) , even though it says -neg, it really is a positive number. Its because you used the positive pressure port. The reading on negative port should be the same number without the -. All vacuum measurements are in columns of either inches of mercury for high vacuum readings or inches of water column for more precise lower readings. Used for measuring very low-pressure differentials, like natural gas pressures, and draft or suction in ventilation chimney systems. Or in our case crank case ventilation readings that need precise readings difficult to get with inches of mercury.

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ok, so air being pushed into the negative side is positive pressure, thats the reason for a + number and air being pulled from the positive side is vacuum is a - number. So for a blow by test t want to see how much positive pressure is in the crank case, gas ect. Pushing past the piston rings, so the hose should go on the negative side? Or it literally doesn�t matter which port you use, you would use the opposite of the reading? If thats the case why is there a negative and positive port to begin with? I know it uses atmospheric pressure as its baseline reading(0). Thanks for educating me

Actually, using the two port manometer, one port is left open to Atmospheric pressure ( 14.7 PSIa at seal-level ) so when reading the differential, you are reading how much lower than Atmospheric Pressure is the pressure in the Crankcase...So although the " Actual Pressure " will be about 14.55 PSIa ( 0.15 psi = 4 inh20 ), in layman's terms we call it "vacuum" ( meaning less than Atmospheric Pressure ) in scientific terms there is no vacuum, just pressures above or below Atmospheric pressure , meaning Actual Pressures and not Gauge Pressures... The difference between Gauge Pressure and Actual Pressure is the Atmospheric pressures at that Altitude and Barometric Pressure.... When using the one port manometer you don't have to worry about it because the open port/Atmospheric port in INSIDE in housing and you cannot attach a hose to it .... The two port manometer is mainly used to read two different pressures that are NOT Atmospheric related, but just related to each other like the difference between two points in an air-flow system... I hope I didn't confuse anyone more by trying to explain the Science behind this Info ...

Quotes source post: 20597140

Great information, thanks again for your help, I�ll post the blow by results when i get it done.

Quotes source post: 20597762

Good deal !! All 996 owners worry or obsess over their engine health, but few have the wherewithal to actually do the Blow-By Test ...

so I was performing the blow by test and got a really high number, so not sure what that was all about. But when I finished the test, shut the car off, and plugged everything back together. I had walked away from the car for a moment and then when I came back, there was a huge puddle oil underneath it and upon checking the oil level. It was completely empty. Leak looked as if it was coming from the left front side of the engine somewhere great

It is likely that you blew out a cam plug. Did you have the proper sized holes drilled in the oil cap when you tested? The good news is it�s unlikely that you damaged anything.

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Hey Brandon, thanks for the response. I just had a lengthy conversation with someone at your company on the phone the other day about a possible future engine rebuild. I believe so, I used the link that was placed at the beginning of this thread, got the drill bits, threaded nipples, and the rubber plug kit. The engine was running perfect when I shut it off, there was no oil on the ground at that time. A: what could be causing the pressure to be so high? B: it has to be something I did, I’m assuming. Was it because it wasn’t relieving the high pressure that was present through the AOS, since I had it blocked off?

Quotes source post: 20603081

also I originally said it came from the front, what I meant was the part of the engine facing the “front” of the car in other words drivers side where the transmission mates to engine

@jdb1994 61 inH2O is crazy high........yes you most likely blew out a rubber cam plug... Just push it back in .... ( if you can find it ) The most I have seen is 36 inH20 on an engine with a scored #6 cylinder....

Quotes source post: 20603132

do you really think I have that much blow by or is there something else going on? I didn’t see anything that looked like a plug laying on the ground. How big of a plug are we talking and can I reach it from laying on the ground? I’m having it towed home, I was at work when it happened, lol. Thanks again

Quotes source post: 20603147

If you had the precision .221 orifice open during the test, then yes, that is your blow-by .. If you have a 996.2 then the Rubber cam plugs are pretty large at about 60mm, if it's a 996.1 they are considerably smaller ( and harder to blow out )... On the 996.2 the bank 2 passenger side is easy to re-install just laying on the ground, but the Bank 1 drivers side is harder because you have to reach up over the crossmember/suspension.

Quotes source post: 20603271

I have a 2001, 996.1. Test cap only has two openings the large one for testing AOS, which was plugged and the .110 for testing blow by at idle.

Quotes source post: 20603301

So you were testing at idle with the .110 orifice open and got 61 inh2o? ....WTF ? Mine was 4 inH20 with 150k hard miles on it ...

Quotes source post: 20603301

Where was your meter connected to..?

Yes if we are going to help diagnose your engine plus read your mind we need ALL the details of what you did ......lol

Quotes source post: 20603353

I'm thinking the test procedure was misunderstood... " the large one for testing AOS, which was plugged and the .110 for testing blow by at idle." With the aos test port plugged, meter was mistakenly on the .110 vent port and no vent port was being used so it blew out a cam plug and dumped oil on ground....

Quotes source post: 20603332

yes, exactly. I triple checked that I had the right hose disconnected from the intake had both of those ends plugged. I don�t understand, the AOS test was perfect. Wouldn�t that have shown something as well? If the pressure was this high or no? It was much higher before the temperature got all the way up over 180. When I started the car, I guess it sat longer than I thought it did from running earlier so the temperature was a little shy of 180 so it was like in the high 70s, before it got to operating temperature. I did notice oil in that tube that I disconnected from the intake. But I�ve seen oil in intakes before so I didn�t think much of it.

Quotes source post: 20603335

the .110 port

Quotes source post: 20603373

so if there�s supposed to be a vent port opening left open, then I did the procedure incorrectly. I thought all openings were to be plugged and the tube was to be connected to the .110 port.

Quotes source post: 20603389

I checked the AOS using this method a few days ago and it gave perfect numbers, using the large port(to be clear)

Quotes source post: 20603395

Thats what i thought, that explains it. There was a misunderstanding of the test procedure for the idle blow by test. The meter still needs to be connected to the aos test port just on the positive meter port. The .110 vent port needs to be open to allow engine to vent a 'metered' amount of blow by. With the meter the way you had it set up, it blocked off the .110 port and you also had the the aos test port "plugged off" not allowing the engine any where to vent excess blow by so it blew out the cam plug...

Quotes source post: 20603407

Great, I�ll probably read that six times to make sure I was doing it right before I started this. Still can�t believe it didn�t blow the little tiny rubber plug out of the AOS test port if it built up that much pressure.

I really appreciate everybody�s input more than you know. I have one last question before I sign off for now and begin to reverse the damage caused by my ignorance. Is it safe to assume the cam plug is reusable, or should I just order a new one? Thanks again

Well, that explains everything. ...

Reusable

Update, blow by test showed 4.1 inh2o , chart says 58 LPM so divided by 4 = 14.5 actual LPM, seems a little high for only 86k miles compared to other readings ive seen here. i have pics of cylinder bores, bank six def looks suspicious. Lots of oil built up on that side of the engine and there was oil in all the spark boots on that side as well, so will have to order new ones. #6 #5 #4 #3 #2 #1

Yeah #6 got a little something something going on in there ... I imagine that is why you started doing the investigation ..

Quotes source post: 20608877

Just doing my due diligence, after the oil report came back. Porschetech3, what are your thoughts on the blow by test results? Thanks

Quotes source post: 20608900

Did you fix your oil leak before doing the second test ? A leak like that will definatly "lower" the test results.... 14.5 Liters per minute Blow-By is about what my 150k mile 3.4 engine has that has been Tracked Hard and turned to Red-Line on every drive for the last 18 years I have owned it... It has never smoked not even a puff of smoke ( except when the AOS failed that started me Inventing the UAOS ) and the cylinder Bores still look pristine ...

Quotes source post: 20608953

there was no oil leaking after the oil change and examining the engine for leaks, also replaced the brake booster elbow today that had a leak after a smoke test. The engine was brought up to operating temperature and driven for 20 min with high rpms with no leaks to be found.

Quotes source post: 20609002

Wow.....with that huge puddle of oil under the car that you took a picture of, the source of the leak should have been obvious and easy to locate........... I wouldn't be able to sleep at night without positive confirmation of the source of that puddle .....

Quotes source post: 20609265

yeah, I know, but I guess the puddle wasn�t as big as I initially thought. When I dumped the rest of the oil today, I still had almost 7 quart�s in the engine. But now I�m afraid to drive it, but what can I do? Cant just let it sit in the garage. Just drive on and watch my oil pressure I guess.

Quotes source post: 20609270

I would have been meticulous and careful about disturbing anything until I verified where that leak was coming from ... I would have just topped off the oil to full and cranked it back up and put it under the same conditions it was ( but not by putting it under 61 inh20 pressure , even though that is only about 2 psi, it is a lot for crankcase pressure )... I would clean all traces of oil off dry as a bone, then drive it aggressive for just a few seconds and check for oil, if ok then drive for a few minutes then check for oil,...if OK then drive longer in stages until confident there is not huge leak...

Would a smoke test help locate the oil leak?

Quotes source post: 20609277

No, Smoke Test is good for "Air" leaks...... For oil leaks it is best to just clean it bone dry then carefully and meticulously look for the first sign of oil.......Big leaks will show first and quickly and smaller leaks will take longer to show...... On small leaks a "Dye" can be helpfull to see with a UV Light ...

Quotes source post: 20609002

So,,, we went from the EXon Valdez oil slick to no oil leakage with no repair..??? With no clue where quarts of oil leaked out of..? Sure you already did, but just asking. How did you clean up all that oil from engine, or did you..? Be easier to see where oil might be coming from with a dry clean engine. Be careful of oil on tires, it can cause problems. Are you the one doing all the work on this car...? If it were me, I'd do exactly what PT3 suggested in the 'blow by thread' post # 263 last paragraph. There is a breather on early m96 engines on 1 valve cover, not sure if this is even possible to be where all that oil leaked/pumped out of when crankcase was plugged off completely, maybe PT3 would know...

Quotes source post: 20609644

Yes, I�m doing all the work myself. I wiped everything down. I was gonna spray degreaser and hose off, but decided against it. Whatever happened it happened from the pressure on the crank case and has somehow sealed itself back so a valve would make sense in my opinion.

Quotes source post: 20609644

It's not plausible the vent valve you are referring to would be the source of a big oil leak as it is below the oil level and there should never be that much oil up there in the breather lines, unless a major piston/cylinder failure had happened.. That vent valve is an over-pressure valve meant to open under very high pressures (2-3 psi ) and is there to keep from blowing out the cam plugs...But Porsche deemed it unnecessary and it was eliminated in mid 2002 and up models.....So I usually recommend just capping it off due to it being a source of oil mist seepage and air seepage on many cars ....

Quotes source post: 20609842

Just trying to clarify, when you said �vent valve is below the oil level� did you mean above? Also you mentioned it would take 2-3 psi in the crank case to push oil through that vent, in one of your comments above you said the amount of pressure that i created on the case would�ve equaled about 2 psi, wouldn�t that have been enough to cause the oil lose? Thanks again for your help, just picking your brain.

Quotes source post: 20610759

Yes I meant "above" the oil level....I'm getting old....lol That vent valve opens at 2-3 PSI, but even if it opens from "pressure" it will not have any oil these because there is low "air flow " ....... To have any oil at all near that vent valve you would have to have extremely high actual Blow-by that "causes" high pressure...... Your high pressure was not caused by high blow-by but rather from you blocking all exits... Besides that vent valve is on the right rear of the engine and not the left front..

Quotes source post: 20610807

Ha ha no worries, me too. When you say right rear, is that drivers side rear? Because I�m 99% sure thats where this leak came from, thats the only part of my engine that has oil on it, other than some on the passenger side, top front. I know I've written a lot of different posts with a lot of info and wasn�t sure that you saw that I wrote that�s where the leak looked like it originated from. I also have a small leak from that corner of the engine thats been present since purchase. It leaks enough that it makes a small puddle on the floor when parked, cant tell where its coming from exactly, other than it looks like its up high. Does the AOS have a seal that could be leaking or are there any specific hoses or seals I should try to get my eyes on? Thanks

No, right is (LHD) passenger side. This picture is looking against direction of travel, which in turn is indicated by the arrow. The AOS sits where you describe seeing oil. perhaps the below between engine case and AOS failed From normal pov, looking in direction of travel. Coincidentally, that is also where the hose to the AOS is connected to evacuate bank1 blow-by. AOS and bellow marked:

Update, I believe i found the leak thats happening when case has above normal pressure. Did another smoke test after replacing brake booster part, which revealed the front intake plenum completely off on the back side. After repairing that I did the test again, my son noticed oil leaking on the ground, so I guess the smoke machine created just enough pressure to show the leak, weird. Any ways its coming from a tiny hole marked in yellow on the pic below that I borrowed from the last post.

Quotes source post: 20611087

Great pictures, thank you. I have actually oil build up in both of those locations, by it drips to the floor on the drivers side rear.

Here are some pics of my engine and areas of oil build up. 1. I believe this the bellows that you referring to, def looks like some has been messing with that, doesn’t look a factory band on there 2. Passenger side front of engine 3. Area where i noticed oil leaking while under pressure and maybe slightly leaking during driving and parked.

Clean that nasty thing up !!! That picture of the lefft rear ( near the bumper on passenger side ) just looks like a little seepage over 10's of thousands of miles.. If you clean that mess off it will probably takes 10's of thousands of miles to get back in that shape .. Plus I highly doubt that you blew the O-ring out from under the scavenge pump...... Stop assuming and do like I mentioned earlier... clean it bone dry then look for the "first sign " of oil wetness...

Quotes source post: 20612139

Ha ha, yes full engine degreasing is next on the list, but maybe you misunderstood my last message, I�m not assuming, I literally saw oil dripping from that small hole that i circled on early post. Here�s a video.

Oil in pic 2 is most likely power steering fluid (pentosin chf11) since the pipe runs there. Good catch on the oil drip/drop. It almost looks that the plug has a tiny hole in the center. I also noticed a drop of green/yellow coolant in the background of your video. That is probably giving the greenish hue on the round cover (of the scavenging pump), next to your leak.

Must be a Northern Car for that Steel Plug to rust completely through with all that oil on it .....LMAO

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OK, so it is a plug. Next question is can it be replaced? And yes, Carfax says it came from Oklahoma before it ended up in Florida for the last several years.

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Yes it can be replaced

Quotes source post: 20613355

What are you talking about ? I didn't know you had high crankcase pressure ........... This Thread is about "blow-by engine health test " ( not the usual AOS Test ) ...

Quotes source post: 20613832

Please elaborate on what it is you are trying to do exactly ... I don't want to assume anything and give bad directions ..

So lately I noticed my oil consumption was starting to get worse. Also noticed puff of smoke out the back when starting sometimes. Back of my mind told me it must be the AOS, because bore scoring should not happen again with my steel liners. Today I got a CEL - P2098 Post Catalyst Fuel trim System too lean bank 2. I started it up and removed the oil cap and heard a lot of hissing. Is this indicative of the AOS going bad, or do I really need the manometer? UAOS has been on my radar, so I going that route if I can confirm my AOS went south.

Yes you need to test with a Manometer....."feeling" the vacuum is only valid if it is way out of specs, and you are very experienced/Pro.....otherwise you need the sensitivity of the Manometer in the inH20 setting..

Quotes source post: 20637769

The manometer I have cost $30. Amazon Amazon I verified my engine with this test. I'm running a ridiculous amount oil over standard full, no CEL codes, no puffs of smoke, and the same used oil analysis results before and after. I am biased, but why mess around with the risk?

Quotes source posts: 20637781, 20637823

Thanks Skip! Hope you are doing well. That is the exact unit I just bought from Amazon, along with a URO oil cap, and the plug kit. Thanks.

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I'm out of the Hospital and still breathing !!! .. Just to be thankful for every day I actually didn't feel that bad untill the morning I called 911 and went into the Hospital .. They put 2.5 quarts of Blood in me then looked for a leak ( didn't confirm one after 6 tests ) and watched me for 7 days then sent me home... Evidently the leak cured itself , (unlike mechanical things) ...

Quotes source post: 20637769

You likely have a vacuum leak allowing unmetered air in after the MAF and why you're getting a lean code. Test with a smoke machine and you'll find the leak.

Ran the AOS and Blow by tests and want to add my results to the results bucket. I'll also appreciate any comments/suggestions/etc. Car: 2000 996 C2 Coupe w/Tip 67k miles on engine Test conditions: Engine at full temp. Elevation: 7000 ft (Taos NM) AOS was replaced about 2 years ago. I Zero'd the Manometer prior to all tests AOS test: All ports/connections connected Test results: -6.49 In/H2O. A touch high, I'm thinking. Strongly considering the UAOS. Blow by test at Idle: AOS to intake disconnected and plugged (both sides), purge valve connection disconnected and plugged (both sides). Oil Cap has the .1110" hole in it. Test Results: Started down around 2 and built up over about 20 seconds to around 3.55 In/H2O I also did the Blow by with the purge valve connected. Results started up around 5 and dropped down to 3.5 In/H20. By my math the 3.55 In/H2O translates to roughly 13.5 Liters/Minute. Also a touch high? AOS test. Engine connections all normal'ed up. No hole in cap. Blow by Test at idle. Both AOS & Check valve disconnected & plugged. Hole is .1110"

Well my first attempt at hooking up a manometer ended in failure. The URO oil cap will not screw on - I guess the fitting is in the way. I'll have to order a black cap like the one on my car, without the ridge in the middle. [EDIT] I forgot I bought the plugs, so I plugged the original hole and drilled in the center. Going to let the gasket sealer cure and try again tomorrow, although I'm not 100% how airtight it will be given the plug gets pushed up to being flush with the hole thanks to the location being right over the ridge on the filler tube. I ordered another URO cap (I can't find the black ones) so I don't need to worry about the plugged hole.

This is testing just the AOS. Car warned up and at idle. Good or bad?

Quotes source post: 20657164

Ya, can't read the mode of the meter, but should be in ' inches of water column (H₂O)' 3.81, a great reading as long as its in inches of water column (H₂O) . If reading is below 6 should be good to go. Closer to 4 is even better.

Quotes source post: 20658863

Yup, the reading is inches of water column (H₂O). Guess I have to continue to research my P2098 code. I was really hoping it was the AOS, which would also explain some increased oil consumption and make purchasing UAOS WAF friendly. Back to the drawing board (or uh, search engine).