excess oil

Hello everyone. My 91 C2 had a 45k service done 2 weeks ago, including valve adjustments. Yesterday, the car started doing something where it almost stalls when the gas is let off at a stop (in nuetral), then suddenly catches itself and returns to normal idle. Also, the check engine light stayed on for about a mile or so today, during which the oil temp kept rising a beyond normal. When I stopped, the car almost stalled, then the light went off, the temp went down and it ran fine. Then I noticed that the oil level gage seemed high. I checked the oil stick and the level was above the high mark. I don't think it was like this before today. I also noticed a little oil on my garage floor, and this car has never leaked before. What might cause the oil to be suddenly high and leaking? I will take it back to the shop for correction, but any thoughts re what I should be sure they check or do would be appreciated. Thank you.

I just got a 91 C4 recently (actually I don't really have it yet, but the deal is pretty much locked down unless a PPI indicates a serious problem). I'm no expert on the 964s since I don't even have the service manuals yet, but I think I remember reading something about problems regarding over filling the oil (maybe your mechanics over filled it during the service).

If I recall correctly, and anyone ***PLEASE*** correct me if I'm wrong, but when the oil is over filled on a 964, it can actually end up being sucked into the intake. Like I said, I'm no authority, but I would think that if oil made it's way into the intake and any sensors, it could wreak havoc on the electronics of the system when it comes into contact with those in the intake.

Hope this helped.

Bill Wagner

The atmosphere in the oil system, including the tank and crankcase is all part of the fuel vacuum and intake system. If you remove the oil filler cap, it affects the idle. If your shop replaced oil lost during the valve adjustment, they may have done it on a cold engine which would account for a gross overfill once the engine warms up and the entire system is flowing. My son once overfilled my old SC and the smoke was embarrassing.
I'd drain the system and see how much comes out. I find that only about 8+ quarts actually drains from the full complement of 12 qts on a warm engine. If you drain out a lot more, it deserves to be removed. Replace 8 qts, warm it up and adjust to the proper level by adding what's necessary.

Hi Tom,
I posted this on the Rennlist as well, but I thought it might help someone over here too.

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I have a 90 C2 and I have just gone through this problem. The gauge is useless on the C2. If you overfill the oil tank you will have the oil migrate to the induction system and you will find you now have an oil leak from the shaft of the flapper valve in the "secondary" plenum. This is because the oil has pooled there.

I found this out when I developed an oil leak after a service that overfilled the tank. I took my digital camera and reached around the engine on the airbox side and got some really interesting pix of it. My question was - what is OIL doing in the induction plenum ??? Another lister told me of his experience with his C2 doing the same thing.

I have lowered my oil to the bottom of the dipstick - so that it JUST registers on the stick. This has stopped the oil tank from barfing the excess oil out of the overflow and from getting into the induction system.

If you look at the schematic of the oil tank you see that the vapor recovery lines are BELOW that overflow vent. So when it is over flows it first goes into your induction then vents.

Try these things to clear the problems that this overfilling will cause.

Get the oil down to the lower part of the dipstick. Measure this when the engine is at operating temp, on level ground and idling. Check it 2 or 3 times to ensure you get a correct reading. (You can drain the oil out of the thermostat in front of the right rear wheel, if you have to)

Go for a drive and accelerate hard to get the engine to bring the "secondary" plenum into action. (Above 4000 RPM - apply full throttle)It will take a while for the oil to get pushed out of the plenum - and it's fun !

You may also notice oil leaking near the thermostat - that is from the overflow vent. It drips down the inside of the oil tank. As the oil returns to the lower level you are now running it will stop coming out. You may want to wash this area out at a do it yourself car wash.

I hope this helps ! If you have any questions email me.

Tom Sharpes 90 C2 Targa http://members.rennlist.com/5150targa