Hi all,

I have a 1987 928S4 Automatic that is using oil and burning it. The car just had its engine refreshed (rings/rod bearings/head gaskets/intake seals...). Before the rebuild, it was using NO Oil at all. After the rebuild it started using oil and we cannot figure out why. Ran a compression test and the cylinders are running 195-200psi. Leakdown was 5-6% across the range. We checked the oil breather line and it had oil in it. The car will puff burned oil (blue smoke) at start and high rpm. I did notice that when i leave the car unused for a week or more, there is no smoke at startup at all. I left on vacation for a month and a half.. came back started from 1st crank and no smoke at all. The smoke at start is worse when i use the car daily. Please help.
Another problem i have been seeing is a vibration in the car in the range of 1600-2000 rpm that is throttle position dependent. If i press hard, no vibration. If i go really easy there is no vibration. At other throttle positions, i have a shake in the car. I have brand new engine mounts. Help again

Sincerely,
Khaled

 

Why was the engine rebuilt? Who rebuilt it? What's your oil consumption rate (how many miles per quart?) It's perfectly normal to find SOME oil in the breather lines. Were the valve guides replaced?

 

I rebuilt it at a well known 928 expert in AZ. I had a problem with my water pump impeller and we thought we had lost the head gasket so we took the engine apart (found out it was the plastic waterpump impeller loose), but since we were there anyways i had the engine bottom rebuilt (i did not damage the head gasket, but replaced it anyways). I did not have this smoking or oil use till after the rebuild. I did not change the valve guides though. But the funny part is that if it was the guides needed changing, the longer the car sits, the worse the smoke will come out as the oil would be seeping for an extended period of time into the combustion chamber. This is the exact opposite of what is happening to me.

P.S. love your 928GT. My friend in Saudi has a 91 GT all specially optionned. He passed away and the 928 is sitting in the garage now

 

Thanks for the kind words about the GT. What options does your friend's GT have?
The most common symptom of worn valve guides would be burning oil after deceleration. You're travelling at 70MPH, slow to 40MPH and notice some blue smoke when you accelerate again.
I wonder whether you have a vacuum line switched and are pulling blow-by oil into the intake.

 

Just outta curiousity....what are the odds on a rebuilt motor to have a thrust bearing issue? Perhaps there could be an alignment issue with the crankshaft?

 

The symptoms are not consistant with either a thrust bearing or crank alignment issue.

 

Not knowing precisely how the breather works, I'll just offer up that the symptoms are consistent with something wrong in the cam cover breather system. Oil drains out of the cam cover area with sitting. So, no oil on initial start up after standing a long time. Oil appears once the area is refilled.

In reassembling the motor did they leave out the inside fittings in the cam covers that serve to condense oil out of the mist before it can get into the breather?

All the other potential causes (rings installed wrong, bad guides) I can think of don't explain your observations. Sorry I can't offer exactly what would be wrong, but at least I think a likely location is the cam cover area.

Nothing comes to mind for your odd vibration other than motor mounts. I can't see why that would appear now.

 

Not starting off with synthetic oil are we? Everybody I know recommends starting a break in with dyno, or the rings never bed in...
jp 83 Euro S AT 49k

 

Dyno or synthetic, that's not going to explain the symptoms. It really does sound like a breather issue.

 

All,

Thanks for your feedback. I think the concensus is that there is something wong with the top side of the motor (breather connections, vacuum fittings/lines or crank covers/oil condensers). I am praying there is nothing with the rings or so since the compression came back 195-200 psi on all the cylinders and leakdown was 5-6% which indicates a healthy motor. I will ask my mechanic to investigate verifying the vacuum connections into the intake as well as verifying oil presense in the intake. I think they have to pull the intake and cam covers anyways under warranty as the paint is yellowing up . I will investigate all things on the top side and hope for the better... but thank you all for all the support. As far as the vibration is concerned, i think it is related to motor mounts too... i will get the shop to check them out too even though they are like a year old with less than 10k on them!!!

With respect to my friend's car, it was a special order 1991 928GT made for Saudi Arabia, it was Forest Green Metallic with Black interior. I think it had all the options that you can think of including leather everywhere (including dash, consoles...) and wood interior trim (very rare). That was one of the fastest car i have ever been in and we had some great stories in it. I think it is a one off considering the options in it. It is sitting in a garage now accumulating dust for the past 3 years. I don't think that car will ever be driven again. Many of my friends back in Saudi used to buy the 928 since it was water cooled and ran better in desert environments plus it was the ultimate GT hands down untill it was killed. Most of the guys still drive them regularly.

 

There have been reports of a few new mounts failing precipitously after a short time. Easy to check. Hope the oil issue is located quickly. I agree rings and seals would not explain your observations.

 

Thanks for the info, sounds like quite a car.
Good luck on the intake issue.