The dreaded oil in coolant

Hi. Ive dont lots of work on my 996tts, 951 and 928. A friend asked me to look at his 2000 996 with oil in the coolant. I gave him all the terrible scenarios and he did his research despite that he wants to take the plunge. So it was dropped off at my house today. 200,000km tippy. The plan is to flush the cooling system replace the oil cooler and cross our fingers. If it works I'll do the IMS. If not..... I've don't coolant pipe pinning and clutches on my 996tt. Any gotchas on the NA I should look out for?

You are a good friend! Good luck with the project 🤘🏻

You've got a lot of DIY experience, why not fab a few pieces to pressure test the oil cooler first before parts swapping, be sure to test the cooler cold and hot.

It is most likely a cracked Bank 1 head....But you probably already know that .....There is a reason we knick-named it the "Y2K Syndrome " ... A new head is $3K but there is quite a bit labor involved...

Removed the oil cooler. Not as difficult as I thought. Someone was in there before and replaced the seals with lots of sealant. Sludge came out of the oil cooler which is a good sign? I flushed the engine and reservoir till no more oily bits came out. Moving on to the radiators.

That looks horrible, but possibly also like a simple fix for the problem. I would definitely recommend pressure testing the heat exchanger. I did this myself using simple tools; - Took 2 washers that fit the holes of the oil coolers - Put a car tire valve in the hole of 1 of these washers - Took an inner tube from a bicycle and cut it up in the same size as a washer, used this as a 'gasket' between the washer and heat exchanger. - Put the washer with the valve + a piece of inner tube to seal it over 1 hole, clamped it down with some C-Clamps - Took the other washer and put the inner tube between the washer and heat exchanger hole, clamped that down with a C-clamp too Pressurised the bit with a pump and observed the pressure. No drop.

I bought a new oil cooler. It should arrive by the weekend. I pulled the right radiator and flushed it. Man what a mess. Doubt the radiators were ever cleaned.

Am I wrong to assume that since the car has over 124,000mile on it which in would equate to 200,000miles because Japanese driving consist of slow, stop and go traffic, with that mileage the heads would have cracked ages ago. If they cracked due to casing flaw then definitely, crack due to overheating most definitely, crack due to heat cycles F yeah. Please school me in my logic.

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To answer your question... 996.1 heads crack because of the oem plastic water pump impeller pieces that break off old water pumps and then always seem to clog small coolant passage ways in the head. This cause very hot spots. These hot spots are the cause of cracks that cause oil in the coolant as the crack happens usually in a passage way that is very thin and adjacent to the high pressure oil gallery. So the oil pressure is higher than the coolant pressure so oil leaks into the coolant.... Jake from FSI or Charles from LN (can't remember which one, might have been both) says its takes about 9 months for the crack to develop after water pump failure/replacement. Not sure how the exact month the failure will happen is computed, but thats what LN/Jake said. Its right here in a post somewhere by either Jake or Charles. Len Hoffman the m96 head expert agrees about the impeller pieces and says very much the same thing, adding that when he back flushes a cracked 996.1 head he usually always finds impeller pieces. Note, this is only a 996.1 problem, 996.2 do not have this type of head crack problem. Anyhow thats the gist of it...

Good to know. Thanks

Bottom line is to get on a rotation to replace the water pump every 5 years or so and you have one less failure point (cracked heads) to worry about.

Yes, replace the water pump and you'll be fine, but from what I've been told, it was mostly one the year 2000 cars that had the issues (head cracks) and it was already fixed for 2001 onward cars???? Just what I've been told and heard

From Len Hoffmans site... THE m96 Head Guru 996 Cylinder Head Crack Repair We have seen cylinder head cracks in all models of M96 engines used in 986 Boxsters and 996 911�s up to and including model year 2001, but the 3.4 996 cylinderheads are far and away the worst offenders. https://hamheads.com/2016/10/20/m96-crack-repair/

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Yep

Put it all back together. Starts and runs fine. Very little oil sludge in the coolant reservoir. Got it warmed up but not enough to trigger the fans. Tomorrow I'll pull the spark plugs to see if I can see any cracks. And I'll remove the water pump to see what condition it's on. The engine is sooooo smooth and quiet. Hard to believe it may have cracked head.

Coolant came out cleaner than the first time. The water pump looks ok.

Is that the original water pump ?

It could be but I doubt it. Couldn't find a date code. It looks similarly corroded like the rest of the block. Awaiting for a new endoscope to inspect the spark plug holes. My TT doesn't have air injections pipes connected to manifold. Do all 996 NA? The make access � PITA.

Got the thermostat to open and radiator fans to come on. A bit more oily sludge came into the reservoir I was worried when I saw brown sludge then I remember I didn't raise the rear nor completely warmed up the engine so there was probably lots more sludge in the system. The borescope arrived late lastnight so I'll use it today. Wish me luck.

Pulled the spark plugs. 1 and 3 holes look perfect 2 had something at the bottom. Hard to tell if it's a crack. Bores look clean. Looks like this engine was out before. I wonder if it's a dealer replacement engine...

Enjoying following along, please continue to post updates. I don't think it's a dealer replacement engine. Dealer replacement engines typically have an "AT" in the stamping after the M96/01. It would read M96/01AT66X11678 instead of M96/0166X11678.

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Yeah, it may be a relatively new water pump or maybe not. But without service history records, you may not know if the previous water pump shredded a fin that lodged in the head and the water pump was then replaced and the previous owner didn't know to try to flush it out, couldn't get it out, or just didn't know any better. Most Folks dont realize that... 1. It's pretty easy to prevent the risk of cracked heads by replacing the water pump every 5 years or so. 2. Just like most folks dont realize that the factory AOS should be upgraded to the UAOS to prevent hydralock which is what cracks the cylinders. 3. Nor do they realize that they can also prevent intermix from the AOS by moving to the UAOS T which eliminates coolant passing thru the AOS. Three simple fixes with keeping your water pump fresh and upgrading your AOS to the UAOS.

Let me see if I get this straight. The car has intermix. You drained everything and checked a bunch of things but did not find any glaring problems. It is now running smooth?

That above pic of your water pump is not the original pump for sure. It looks almost new like its been changed out within the last year. This is what an original oem 25 year old pump looks like...

Always ran smoothly except for the intermixing. It was bubbling from the reservoir but I'll attribute that to the PO not venting and bleeding the system properly.

My guess is the oil cooler failed

Bubbles from the reservoir usually lead to a cracked head but where the exhaust fumes are passing through. There are kits that test for exhaust fumes in the coolant. Just to add to the madness.

Everyone always wants to think its the " OIl Cooler" causing the Intermix ......lol The bubbling out of the reservoir is usually caused by an extra quart or two of "fluid" (ie. oil) getting in the System ....

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Imho, you may want to come up with a list of what can actually cause intermix in the M96 and then test for each. Plenty of threads here on RL on each of the causes, tests you can perform and solutions. Best of luck figuring it out.

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+1, also, the oil cooler can be cheaply tested yourself with a contraption of 2 washers, a tire valve, some clamps and an inner tube. Would be sad to reassemble everything, only to find out the issue was something else, and you'd have to do it all over again.

If it were my car, I totally agree. The engine would be out, stripped and probably sent off to LN for a 4.0l upgrade. Or buy a used GT3 engine and swap that in. But the owner wants to keep the spend low and clean the system. So I'll flush the cooling system again and hand it back. Yesterday I installed some good used tires on the rear. The old ones were showing steel belts. Now there is only a slight bit of sludge in the reservoir I can break it up with my finger. Far cry from before.

Drove it up and down my street swerving a lot to help bleed the system. Got the fans on, a few burps came out when I opened the reservoir cap. Temp needle stayed just right of center for 45min of running. This is the first time I drove the car. Error code 4266 came up for no signal from aBS pump. Hope it's just a fuse or connection.

I think 4266 is the ABS return pump, which means the ABS electronic module is bad. Here in the US we have Module Masters who can fix it. Not sure about Japan.

Every morning there is an oil slick the size of the cap. I swirl my finger in it and it's just there. A shop rag is enough to pull it out. The owner decided to take it back as is. He is happy it isn't boiling over. Probably the previous mechanic didn't know how to bleed the system. Other mechanic friends said it could take weeks or months to clear the system of sludge. I'm somewhat confident the oil cooler was the issue. They the previous mechanic changed the oil just before I got it. The oil slick smell like old oil and isn't mixed or frothed. Just a simple slick. Anyway it's gone and everyone is happy.