2001 M96/04 3.4 intermix could a cracked cylinder head pass a pressure test

I just bought this 2001 M96/04 3.4 engine for my 99 I got a deal on it boars looked like new with a boroscope but when I removed the oil pan it had some intermix in the pan/filter and some normal used oil. The engine is on a stand and I capped the cooling ports and pressure tested the engine/oil cooler and found a tiny weap.on the water pump after fixing that Its been holding 25psi for over an hour I did remove the AOS as it was the motorsports version on a billet bracket and was leaking oil and the hoses where all disconnected I plan on pressure testing that as well. But I'd think it I had a crack in the head I'd be loosing pressure in the system or would it only happen when warm? Thanks in advance I'm still learing these engines.

I had a tiny Crack and it was definitely losing pressure when cold, faster when hot, but like 1psi / 30min when cold. Not all failures are the same, but this was my experience. Having said that, it's not that hard to (visually) check the heads for cracks once you have it on the stand. Remove the cam covers, cams, lifters + carrier and check it out. Probably an hour or 4 to remove and refit if you haven't done it before. I would do that anyhow, also inspect the cam chain guides while you're at it and test the solenoids. They are prone to wear/failure. ​​​​

I took these an hour apart and my water pump is weeping just slightly with soapy water applied

If the pump leaks, get that addressed. I'm a big fan of a thin layer of hylomar blue on those gaskets, bit of extra insurance. Pressure loss seems absent. Mine lost pressure much faster. OH yeah, and in my case the aos was full of mayonnaise too, that might be worth checking... It all does still raise the question of where the intermix came from. You're sure it was coolant? Happen to know the history of the engine? Perhaps car was flooded? ​​​​

Supposedly it has around 90k miles and was a spare they picked up and never used. It had the Motorsports style AOS from a newer car installed when I got it. Luckily there was no other debris in the pan or filter it was extremely clean except the mixed oil and there was also a mostly clean used oil on top of the mix it probably sat for several years in a shop so maybe the oil and mix started separating?

I'm pressure testing the AOS right now off the engine I'll see what if that shows any change

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PT3 always said, " oil only in the coolant reservoir, its a cracked head" , "coolant milkshake on the dipstick/in sump and or oil also in coolant, its a cracked block/d-chunk or possibly 1 out of 10 times the oil cooler. Also, iirr Len Hoffman said you need a special fixtures to block off all head coolant passageways, and heads removed, test pressure had to be high like 100psi iirr..to find some of/all the common 996.1 cracked head leaks.

I pressure tested The AOS coolant side up to 30psi it's dropped 1 PSI over the course of 30min

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Put it under water and see/where/if any bubbles come out of. PT3 really doesn't like the oem AOS or the Motorsports AOS, but don't remember PT3 ever saying anything about a faulty aos causing intermix. ?

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No signs of oil in the cooling system just coolant mix in the oil pan The long block with the oil cooler installed are pressure testing good I just resealed the water pump gasket and I'm redoing the test just to confirm The AOS was the later Porsche Motorsports style and it lost 1psi over 30min maybe it's cracked internally and dripping into the sump? I boroscoped the cylinders and they looked great

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That's brilliant I'll do that tomorrow I wasn't planning on using it anyways but I'd feel a lot better nailing down the cause of the problem beyond reasonable doubt I'm going to leave the engine pumped up at 25psi over night and see what it looks like in the morning

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Hate to say it,,, but need to be honest with you. Agree It would be nice to know where the intermix came from. But at this point, after your above testing/observations ruled out only head cracks, as the sump was showing definite signs of substantial intermix being pumped throughout engine. So, Regardless of your non-conclusive pressure test results, engine must come totally apart, as at the least the babitt crank bearings get/got destroyed from coolant/intermix that was being pumped thru them, and everywhere else. So even if just the oil cooler is the reason for intermix, the internal damage has already been done... Did you scope from spark plug holes or sump..? jmho

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Thanks for your input and those are valid concerns I'm not too worried about the bearings right now as there where no signs of wear or partials in the sump and filter I do understand that coolant mix isn't the best lubricant but the percentage of clean oil to mix was 75% clean to 25% mix so I think I'm going to risk running it for now. This is a spare engine I purchased cheap so I can enjoy the car. While I focus on rebuilding the original motor that still runs but has other issues. I did the boroscope down the spark plug holes when I got it and now that its on a stand with the sump off I peaked in there and it looks flawless no concerns there the Oil cooler was also pressure tested and passed. I believe the mix problem was actually caused by the AOS. And I've got a new one from Porsche I'll be converting it back to the Standard when I swap over the intake manifolds from my 99 motor

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When Skip (@Porschetech3) heals up hopefully he will see this and can give the details, but in his UAOS design, he eliminated the coolant lines going thru the AOS due to the heat generated off of the engine in its new location which was an intermix failure point with the factory AOS. Dont know the probabilities of it happening, but its one less thing to worry about.

While you are cleaning up the sump replace the swirl pots with ones from a 997 . They flow better and not much $$$ . Good luck with the engine .

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Thanks I'm down in SW Florida and was thinking that the coolant line are probably not needed in our climate but figured I'd go back together stock for now. I'd like to do the UAOS in the future but I'm trying to keep this a budget build for now. I got this 99 996 coupe 6spd for 10k knowing it needed an engine overhaul it ran and drove no smoke on start up but it has some rattling noises off idle and I found some glitter in the oil filter. So I planned on doing an overhaul but figured that would take several months maybe longer depending on weather lol DIY at home at this is the first modern Porsche Motor I've worked on. I usually work on Subarus Bmws and old Mercedes Diesels. But this used motor popped up for 5k with 90k miles and a good compression test from when it was removed i boroscoped it before taking it and checked the dip stick and it was clean oil. I didn't find the mix until I got it on a stand and could remove the sump and filter. The PO said he had just replaced the AOS before removal and it looks like it was a used Motorsports style unit with Billet bracket and the lower 90 hose wasn't installed very well causing an oil leak I don't believe it was on the car long before it was pulled.

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Its not so much the lack of lubrication as it is the chemical reaction of coolant to babbit. When ethylene glycol contaminates lubricating oil and is subjected to engine temperatures, it oxidizes to form organic acids (such as glycolic, oxalic, and formic acid) that severely corrode the lead/tin overlay of Babbitt journal bearings. You won't see signs of wear or partials in the sump and filter from this type bearing corrosion... So just know this, and proceed as you must, keeping in mind the very expensive crank might be salvageable now, but if it spins a EG corrosion/pitted damaged bearing, $6K crank will be junk... .

I was told this IMS was replaced. I'm going to need to do it again before I swap it in the car. Is this LN engineering or stock?

Duplicate

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I understand the risks. I've rebuilt/ fixed a tons of motors and have seen several that had failed head gaskets especially in the Subaru world and more often than not the bearings survived I'd say 80% to 20% There's a good chance my other motor will need a crankshaft because of the glitter found in the oil filter. I've found you can buy a complete running 2.7 motor for 800-1800 and apparently they share the same crankshaft and rods if I'm not mistaken

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Congrats on the car! No question, you would rather have the Porsche Motosrsports AOS on your car than the factory AOS. Gives you one less thing to worry about over the near term. You have other refresh items to deal with that are more pressing. Good luck with sorting everything out.

I've ordered several parts and the tools for IMS and Timing 1. New 997 style oil return pipes x2 2. Oem water pump/oil pump gasket 3. LN hardened oil pump Drive 4. OEM Porsche AOS 5. New 997 style Oil pressure Releaf valve/spring 6. New Crankshaft Position Sensor I'll be ordering more parts when I get the valve covers off if they're still the originals I've been cleaning up the engine so its not a ball of Grease that said it didn't look like it was leaking just tipical road grime

If budget stretches. Allegedly the 997 3.8S oil cooler is the biggest that will fit.

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FWIW, you had mentioned that you have a relatively new Porsche Motorsports AOS. If so, I wouldn't waste the time and money on a factory AOS. Instead, I would figure out whats leaking. If you gotta get a new AOS, get the UAOS which is the best one.

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According to my Pressure testing The Intermix was caused by the Motorsports AOS it was also the source of a major oil leak My cars original motor still has the factory style AOS and it was still working. Im replacing it with a stock one for now to keep this on Budget. Once I can verify that everything is working properly and get some seat time in the car the UAOS is on my list of future upgrades This motor also had an IPD intake Plenum but apparently it won't work with my cable throttle as it was eGas The 90� elbow on the bottom was leaking oil on the back of the motor it doesn't seem like there's anything holding it in the motor besides the bend in the hose.

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Sorry to hear. The PMS AOS is substantially more durable than the factory AOS. If its just a hose, it may be worth it to replace the hose. The oil filler tube is also a problem regardless of what AOS you run. I cant remember if it needs an additional part to use on a 996.1. I believe it does. Check with LN, they have all the parts. I have a 996.2 and went thru two Factory AOSs pretty quickly back in the mid 2000s. At that time Porsche rolled out the PMS AOS and I went to it. It was cheaper to do in the 996.2 than the 996.1 because it had less parts. Then I went to the UAOS w/ Track Drain because it is a better design than the PMS AOS for many reasons. In addition to being able to process more oil mist and therefore more oil quantity, having a diaphram that is 2x the thickness of both the F AOS and PMS AOS, and the ease of changing the diaphram in 5 min, it also eliminates running coolant thru the AOS which eliminates intermix, which may be you issue. But to your point, it may be that the PMS AOS failed. It certainly happens. Mine did. In my case, it was the diaphram. Hope it helps.

Picture of the PMS AOS. Notice the aluminum bracket at the bottom. Porsche Motorsports AOS Air Oil Separator 99610792600 https://share.google/5uEB161lZrcTbwT5X

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Did you end up pressure testing that AOS in a bucket underwater and verifying a substantial coolant leak...? Or verifying in some other way, as in the 25 years I've read Porsche forums and owned 7 different m96 engine'd cars, never ever heard of a intermix caused by aos...? And we all know there have been a very lot of intermix reports... Assume, unless there is a large very obvious coolant leak in aos, the vacuum would suck a small amount of coolant leak back down intake and maybe cause a hydrolock..? But Suppose there is always a first...

Yeah, I have never heard of the PMS AOS suffering from intermix. But the PMS AOS does suffer from diaphram failure as well as it has limitations on processing higher quantity of oil relative to the higher quantity that the UAOS T can process.

The rust on the IMSB cover* indicates contact with water, IMO. Either since the car it was in, flooded or when engine sat in storage. Greater chance it was the former. Are you able to find out whether the intermix is with coolant or with water? * cover is cast therefore original/stock. The 12(?)-point nut and spacer behind it, however, is not. Anyone's guess what the bearing inside is.

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This engine was sitting in a shop in South West Florida it's very humid down here so everything bare rusts That said the shop started pressure washing this engine one head was cleaned off when I got it and there was also some water in the oil below the mix luckily there's no signs of rust inside the engine it looks spotless and I don't think a pressure washer could have cause the mix to get in the oil filter. Also none of the bolts on the outside of the engine show any signs of corrosion they are all perfect still have there green coatings and clean threads Someone said this was an early style cover because of the markings so it may not be original on this engine and it appears by measurements to be for a Dual row bearing I was told it had been upgraded at some point I'm going to pull it and then figure out what I need to order just to be safe