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johnmh

head gasket diagnostic? AOS? Cracked liner? Paranoid owner?

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So....

 

I bought a ratty US spec 2001 cabriolet manual with 80,000 miles on it cheap in 2016. Removed the engine and did a deep service, ie IMS bearing, AOS, coils, water pump, coolant tank, timing chain runs and tensioners, belts, just about everything I could think of.  I Installed new rads and fans and a central rad just to let it cope more easily with heat.  Car starts and runs perfectly, never runs hot, no error codes, just great performance out of my 3.4.  So far....

 

So today I changed the oil (almost none consumed over the last 5000 km and it looked remarkably clean when it came out). I check the air filter (still clean) and then check the coolant level (hmm, about a liter or so below the low level with the car somewhat warm). I also noticed some pinkish vaseline type sludge on the rad cap and a bit more pinkish sludge in the coolant tank.  This concerns me.  FWIW, I do not use Porsche spec antifreeze, rather I use Evans NPG coolant. I have been using it with success for years in my other, more finicky Italian cars and thought it may be good in the 996. No coolant pressure at operating temperature means an easier life for water pump seals. 

 

Any easy way to check for oil getting into the coolant? What are the classic symptoms of the cylinder 'D' chunking? I did notice a slight bit of steam rising from the oil filler neck when I drained the oil , but a really minimal amount.  Am I being paranoid?  Ironically, I was offered a local 3.6 for cheap last week, but understand the reverse engineering to get it to work in a car designed around a 3.4 is not remotely worth it.

 

 

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Drain some coolant (not all, just a sample), put it in a glass jar and let it sit undisturbed.  Observe it and see if there is any separation of coolant and oil.  Do the same for an oil sample.  To firmly established whether your engine has D-chunked, a cylinder compression and leak down test on each cylinder needs to be done.  Inspect the spark plugs carefully for coloration and replace them.

 

Synthetic oil is hygroscopic so it will absorb some moisture (humidity) from the air.  It is burned off when the engine reaches full operating temperature.  If the engine has not run and reached full operating temperature in a while, could just be some "steam" you released when you changed the oil.

 

If in fact your engine has fully  D-chunked, it will run very badly and you will get misfire codes.

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Thanks, I will pull the plugs and examine them.  There is definitely a mix of something in the coolant tank. As the Evans does not operate under pressure, I suspect if there is a leak, the oil is being pushed into the coolant, rather than the other way around. Car still starts and runs perfectly, nice and cool, with no residue inside the oil filler cap.

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While I wait impatiently for the tool that can check for exhaust gasses in the coolant, a few issues become apparent (if indeed the car has an intermix problem):

 

The issue is not likely to be a head gasket, but rather more likely to be a crack in the cylinder head or cylinder wall. Is there any other likely intermix source?  The water pump and AOS are new OEM parts and I cannot see how oil is getting into my coolant expansion tank otherwise.

 

If the crack is in the cylinder head, can it generally be welded, or is the best practice replacement of the head (which may raise other issues as valves, cams, etc, may not cope well with being transplanted into a new head. 

 

If the crack is in the cylinder wall, does this mean a new engine?  I have $12k in the whole car as it sits, I am not sure I want to spend another $12 k on an engine.  I can get a new IMS installed 3.6 locally for cheap from a friend, but the wiring harness and DME transplant issues for use in a 2001 996 may not be practical, and that engine may not come with much history.

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Just to provide an update, I used a exhaust gas in coolant detection test (great tool), and, after letting the car come to full operating temperature in order to open the thermostat, it passed. Apparently no crack / head gasket failure, which is a relief. 

 

My guess is that some residual oil remains in the system (even after a fill/run/drain cycle) due to the broken oil cooler on the car when I got it.  I will monitor it and flush it again.  

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