924Board.org

[stevekat]

On to the next issue. My 1981 S2 smokes upon start up for a short time. then it is generally fine. I am trying to determine if it is turbo oil seepage or valve guide seals.

Fuel system should be OK. Engine hoses are probably all good. All elbows replaced, vacuum lines replaced. Car runs great. Starts great, hot, cold, warm. Recent leak down was very nice.

The telltale that I believe probably means the most, as I try to evaluate the clues, is that the smoke starts just a few seconds after the engines starts. This is where the experience on the board might help with my analysis. I believe if the smoke starts so quickly in two to three seconds, and the smoke dissipates rather quickly - perhaps 15 - 30 seconds when driving (more when idling,) that this is pointing to valve guide seals.

My thinking: I do not believe if oil is getting past the turbo shaft into the exhaust side, that the temperatures that exists in the exhaust manifold or turbo exhaust side, just a few seconds after the engines starts is enough to cause pooling oil to burn off so quickly. i know there are hot gases, but at a slightly high idle, the volume is low.

My thinking is that with valve guide seals, oil that has accumulated in the cylinders or behind the valves, having seeped down the valve guides, would begin to burn instantly in the combustion chamber, when the engine starts, and would then appear quickly at the exhaust exit.

A separate note: I just replaced the waste gate and J-Pipe the other day (with a spare waste gate I rebuilt.) Upon opening the waste gate from the car, it was dry on both sides of the diaphragm (on a unit that had been installed in a configuration used for adjustable boost with counter-pressure in the top. I thought this may be an additional hint that atomized oil seeping from the turbo pressure side is not present. The waste gate unit I rebuilt was pretty wet on both sides of the diaphragm when I initially opened it up.

So best guess, based on the above: turbo leakage or valve guide seals?
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[Smoothie]

Holy smokes my peeps - what's with all the 931-specific Q's in General Discussions lately? Can we get back to using 931 Tech?

If it is a valve seal problem, you should be able to make it smoke while driving.. Use "engine braking" to increase vacuum - if leaky seals are the problem, this should pull some oil past them. -Then accelerate and watch out back for smoke.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[stevekat]

I posted to the top forum as over time it seems it has become more central to a wide range of discussion - I get a sense some members check the 931 Tech, and 931 Discussion areas less frequently.

I've tried the off throttle coast, then accelerate experiment but is inconclusive. I do not notice significant smoke, but not sure this rules out valve guide seals. Also, my smoke is on the light side of gray. I do not get black smoke when it occurs at start up. Whatever oil burns does not have a huge impact on my oil level in the engine.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[bnoon]

Just pull the plugs. Oil deposits look dark like burned oil and may be slightly chunky. If the oil is getting into the combustion chamber at all, there will be evidence of it.

If the plugs are clean, then suspect the turbo.
_________________
'80 924 Turbo - SOLD!
1986 Porsche 944 Turbo - SOLD!
Porscheless

[dpw928]

I will get a little smoke at start up if I didn't let the engine idle long enough at the previous shutdown. Guess I need more patience.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[Grenadiers]

My '81 leaks oil out the t/b and onto the intake manifold (suspect turbo cold side oil leak). But, it never has smoked at startup. Since there are what, 3 brass 'seals' on the turbo shaft, could there be a leak on either the hot or cold side, or both? I also have some blow-by on the '81 and little to none on Spike. But, the spark plugs have a very normal tan-like appearance. These cars are weird!
_________________
'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
2004 Winnebago Vectra monster RV
2012 Jeep Wrangler
2014 Kia Soul
2001 Ford F350 powerstroke

[stevekat]

it is difficult to lock down and interpret all the clues. i'll try to eyeball the plugs. that might be helpful if any suspected turbo leak is on the hot side. clean, hot side, not clean, maybe valve seals. Or possibly cold side if enough oil atomizes?
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[tuurbo]

This kind of belongs in the 931 section(s).

[ideola]

I have never seen a 931 that didn't smoke on initial startup. It could just be that every one I've encountered has not been 100% up to snuff. But I've grown accustomed to it, and since it doesn't seem to affect plugs fouling or long term oil consumption, I haven't worried about it.

Steve, I tend to agree with your assessment, that the valve guide seals are suspect. I had this problem on the 941. I borrowed Vaughan's valve removal tool that allows you to remove them with the head in situ, and replaced all of the seals. It made a significant difference, it cut down dramatically on the startup mosquito cloud syndrome (I'm exaggerating), but I still do get a slight oil burn cloud at initial startup, especially when it's been several days between starts.

And FWIW, I get the exact same behavior on both my 928 and 924 NA, so it may not be specific to the 931, it could just be the nature of the valve seal design. Perhaps this is one of the leading contributors to the factory-specified oil consumption rates. The NA has a freshly rebuilt top end with about 15,000 miles on it now.
_________________
erstwhile owner of just about every 924 variant ever made

[Smoothie]

+1^^
Some might even refrain from answering 931 questions asked in GD by regulars that know better - and one would never know.

Ya, I apparently get some smokes at cold startup (just verified it). It starts with no smoke, then starts smoking after running for 20 seconds, and as ideola describes - a mosquito fog, but it disappears within 5-10 ft. It continued to smoke the same for 1 min, 45 sec, then stopped completely as if shut off by a switch. Coinciding with the smoke finishing, the idle smoothed out, and the engine was passed its' usual cold-start slightly-rough-running stage.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Maybe924]

For what its worth mine doesn't smoke on startup. Having said that if I flog it really bad, do the requisite idle for 30 seconds and then start it up in about 10 to 15 minutes it will blow some smoke for a minute or so. I'm pretty certain I'm just squeezing some oil through the turbo seals but its a rare happening and only if I really get on it.
_________________
1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

[stevekat]

My car definitely has some significant mosquito patrol action. At times it is embarassing. Other times very little. If I start it and just let it idle, it seems to more often go for a long time. If I start up and drive it can go away very quickly. Maybe it is just an issue of volume of gases moving through the system to clear. Different starts, it can smoke for different durations, seemingly at random. I tend to run the car for 30 seconds to a minute before shutdown.

If I can get going I am good, but if someone gets in front of me at the corner leaving the development, it can become pretty embarrassing.

I did notice it seemed to smoke more the morning after a long 60 mile drive, rather than some around town driving.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[ideola]

I would definitely check the valve stem seals
_________________
erstwhile owner of just about every 924 variant ever made

[stevekat]

Dan, I think I asked you this question before, but what special tool did you use. I am going to put air into the cylinders. My tech said I should turn the pistons variously to TDC when working on a valve so it cannot drop too far.

What do you use to compress the spring. I cannot remember what I used to use when I had my prior car. I have a clamp on type compressor but not sure that works with the captured spring. I vaguely recall having to use a lever type - but it was so long ago.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[Smoothie]