924Board.org

[kyhm]

Looking for some advice... I'm getting a lot of white-grey smoke when warming up my 931, definite smell of oil. Starts once the gauge gets out of the cold mark, stops once the engine's warmed up. No sign at all when hot, or when re-started after sitting hot for a while.

Dead cold oil pressure reads 8 bar at 1000 rpm, 9 at 3000. Hot the oil pressure's 3-4 at 1000, 6-7 at 3000. Could this be a failed relief valve? Maybe the cold oil pressure's too much for the turbo's oil seals, but once hot it's ok?

Turbo was replaced in Nov 98, but the car's been off the road most of the time since. Odo's broken, but the turbo's definitely younger than 5000 miles, and I'm always careful to cool it down if I've been driving hard.

What pressure should the bypass valve allow, and should I just rebuild it when I do the camshaft oiler? Apparently the spring/piston/washer are cheap...

It's time for an oil change anyways, and I was planning a switch to synthetic... We'll see if that sorts it out. I'm hoping there isn't a new turbo in my future, since *lowers voice so car can't hear him* I'm looking at a 1500-mile road trip this summer...

[numbers]

White-grey smoke indicates water vapor. Blue-grey smoke indicates oil, black smoke indicates too much fuel (rich mixture). It is normal for the turbo to leak some oil past the seals when you shut it off. This will appear as a large puff of smoke on start-up. My guess is that you are smelling this initial puff of oil smoke, and the rest is just condensation from your Cat and muffler burning off as the car warms up.

[kevrl]

The oil pressure in mine never goes above 6.5bar when cold (no matter what grade of oil I use) and always sits at around 2bar at idle (900rpm) when hot, rising to 4-5 bar at higher revs.

I have heard on some cars that some cheap oil filters can cause the pressure to get too high, check that yours is a genuine porsche or VW filter, not sure if this applies to 924's. The standard pressure guage in the car is not very accurate though. I agree with numbers, white smoke is usually just water vapour, if it smells sweet then it could be coolant from a blown head gasket, do the usual checks for oil in the water and water in the oil.

Kevin

[Paul]

I use 15w-50 Mobil and had the same problem, sometimes showing 9 bar when the engine was cold. I replaced the spring in the pressure relief valve and now it never goes over 6.5 or under 2 bar. This is a very simple thing to do, takes about 5 minutes.

[numbers]

Something to think about. My Daddy, who was an Indy Car driver, and a hell of a mechanic, always said, "any oil pressure is enough." So don't get in a tizzy because your guage goes down when your car is hot. If your guage goes to zero, or your oil light starts flashing, shut it off, because you have a problem. But if the guage reads one or nine, or anything in between, and your engine is not making any noise, you are fine. High oil pressure just throughs more oil around the engine, and can cause you to burn a little more.

[Paul]

I believe 1 bar equals 14.7 psi, so 9 bars would be over 130 psi. I was worried that I might blow a 22 year oil line, so I changed the spring and cleaned the piston.

[kyhm]

Thanks for the advice folks, and sorry for the long post!

I'm still thinking the oil's getting forced past the turbo seals when cold. I'll try to get ahold of the (cheap) rebuild parts for the relief valve and change 'em when I next change the oil.

The smoke was around for quite some time; I had the engine idling for a good 15 minutes while I did electrical checks, and every time I revved it another puff. Smelled like oil the whole time too, so I don't think it was pooled oil.

Went out and drove it a few miles, and all smoke stopped, cooled it down and stopped the engine, restarted 20 minutes later, and still none.

Now, the fun part. I've read FAQs, articles, the 924.org tech section, searched the board, etc. but found no concensus as to what weight oil to use. I'm planning to clean out the sludge and switch to synthetic, probably Mobile 1 or Red Line, but I'm not sure what weight to use...

Given I almost never see air temperatures below -10C/15F in winter, or more than 35C/85F in the summer, what's the best weight? 10W30, 15W45, 20W50?

There seem to be lots of 931s in Washington state, which is basically the same climate I'm in... What do you folks use? Thanks!

[numbers]

I always recommend 15W-50 Mobil one for the turbo. The underhood temperatures in the 931 run so high, that anything lighter than 50 weight gets mighty thin in the summer.

[TroyDest]

I don't know Numbers; I switched over to Mobil 1 15W-50 last oil change and am not happy. The motor doesn't rev as freely now, even in the summer here in Sacramento where it gets over 100F. I always have plenty of oil pressure. Next oil change I'm using Mobil 1 10W-30 and hope I get the easier revs back. -Troy

By the way, I used to use Valvoline 30 wt. before I switched to Mobil 1 and have never had a problem with it. I still use Valvoline 30 in everything but my 931.

[ This Message was edited by: TroyDest on 2002-04-16 08:11 ]

[numbers]

Yeah Troy, I moved to Denver from Rancho C, so I know how the weather is out there.

[larso]

The oil is a scary thing to think about because I know for sure on cold starts the 15W50 will cause you to wear your engine out faster than 10W30, but then at hot temperatures the 10W30 will be like water. I think the best consensus is to warm the car up as fast as possible and use a thicker oil, and more importantly keep the engine cool. A low temp rad switch, and removal of the air conditioner I would say is very important. I find that if you are going 100 on the highway there is no temp. problem. But if you are driving in parking lots there is a huge problem. I would say that the temp switch and correct function of the fan could save your turbo and engine a few thousand miles.
If you are switching to synthetic, you may have more leaks. If you already have leaks with dino oil, you will most likely get more with the synth. It's fine to have leaks on a 20-25 year old engine though, I don't know of one that doesn't. Overall I'd go for synthetic with turbo cars IF you do see the temperature gauge get high. I believe in using dino walmart oil on non turbo cars. I believe in using synth oil on the 931, if the temp does creep up. If you have good fans and no air conditioning, and the temp does not creep up...then maybe dino would be ok on the turbo. Some people say to use 10W30 oil in the 931 so that the turbo is always getting oiled (thinner, easier to get through), but I don't know about that since the oil may be so thin that it does not lubricate. Again if your temp. stays down I see no problem with using 10W30 though.
There is also some info about these engines having looser clearances....but, agreeing with numbers, since any oil pressure is good, I think 10W30 would be ok IF you keep the temperature down.

[ This Message was edited by: larso on 2002-04-24 20:13 ]