924Board.org

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Ah.. the nightmare that is my 931 continues.

The Symptom:
Starting from cold, after 30-60 secs white smoke begins pouring out of the exhaust. It's white and steamy, no blue color or burning oil smell. In fact, it just smells like exhaust usually does. After the car warms up, 5-10 minutes, the cloud of smoke goes away and stays gone unless I restart from cold again.

If I shut it down while smokin and pull the plugs I'll get white smoke pouring out of one of the cylinders (#2 cylinder last time I checked). Looking into the cylinders I can see some wetness on the pistons. In other words, the coolant is getting into the combustion chamber.

No froth in the oil that I can see. And the car runs excellent all the time. Even with smoke pouring out the back, the idle is butter-smooth at 800 rpm.

The Remedy:
Must be the headgasket, right? Replaced that over the weekend. Torqued the raceware studs to spec. Started it up and I get the smoke again after the initial 30-60 secs.

What the h*ll???

I can only guess that the head is warped, has a crack, or the block deck is warped. I'll pull the dumb thing apart again and send the head off. If it checks out, then is there anyway to check the deck? Or is there anyway to resurface the block deck without pulling the whole thing out of the car (even if I have to tow it to a shop with the head off)?

Does any of this make sense? While cold, the cylinders must be sucking coolant in, then sealing up again while hot? With the cap off and running, I don't see any coolant bubbles.

Any tests I can perform before jumping into this thing again?

ahhh...!!!

_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

Oh man, you gotta be crying yourself to sleep by now! You need to find out wich cylinder it is before you tear it apart again. Heat it up so the coolant is pressurized then let it cool and pull the plugs. Turn it over by hand untill you can see the top of each piston. Find the wet one. Next, pull the head and have it pressure/vacuum checked. If this doesn't show a problem then chemical dye crack test the entire wet cylinder including the intake and exaust ports.

I really doubt this is a block problem. You can check it with a straight edge while you have the head off. Look for "dips" around the coolant passages especially around the wet cylinder. If there were any cracks in a cylinder this would have shown up when you honed the cylinders.

See if you can borrow or rent a coolant system pressure pump if the first advice does not show a wet cylinder. You need to narrow the search before you pull the head. Also be sure to turn the engine over by hand during the test to see if coolant falls thru the intake valve due to a crack in the port.

Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

My car was doing this. It turned out to be oil, but I didn't recognize it as such because I am running Mobil1, which apparently doesn't have that burning petroleum smell. And, as Paul pointed out, if it had been coolant, it would have smelled strongly of. . .coolant.

(*rasta, you are so full of shit*)

No, really! And here is the reason. . .my intake was restricted by an improperly installed air filter (

), which created a vaccuum in the cold side of the turbo. The cold side turbo seal was spitting Mobil1 into the intake while idling cold. Exact same symptoms! Fitted a K&N air filter, and the problem stopped. . .when it had been laying down a James Bond smoke screen like you wouldn't believe.

Check your intake plumbing between the turbo and throttle body for a light coating of oil. Try starting the car cold without an air filter.

It ain't your head, unless it is bad valve stem seals...this motor sat for a while, yes?

rasta
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

^ Interesting

I've been wondering if my filter was too small. When I take off under boost, I get a good puff of smoke. I remembered from your post that you had this symptom too. I have a very light film of oil in the intake / intercooler / turbo outlet tract. I figured the filter wasn't breathing well enough under boost.

However, I couldn't imagine how a too-small filter would give it problems at idle. Although, if the turbo seals are cold and the intake is sucking hard (I get ~22in-hg / 30kpa at idle), then I could see how it might happen. The only thing that doesn't add up is that it definitely doesn't smell like oil, and my hand is wet after putting it against the exhaust. Plus I can see water droplets beading up inside the tailpipe against the carbon. You had smoke on cold start-up at idle? I'm still running 30wt non-detergent oil, maybe it has less of a typical oil-burning scent?

It's worth a try. I'll do one better and pull the hose from the throttle-body to the intercooler off so I don't suck in anything that's already in the IC.

Thanks for the idea!
Crossing my fingers...
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

My hoses are all 1/4" thick silicone. Not much collapsing going on that I can see.

I'll have to work out a prize if you're right. Although, given your handle, I'm pretty sure I can't send *that* through the mail.

_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

I'm in Oregon, mon. 'Tis better to give than receive!
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Lizard · Posted: Wed Oct 11, 2006 3:39 am Post subject:

I would recommend just for the hell of it a leakdown test on the engine.
_________________
3 928s,

Ozzie · Posted: Wed Oct 11, 2006 8:08 am Post subject:

It can just be condensation build up after a cold night/cold start in the exhaust which boils off with no smell .
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Hmm, it's 6:45 in Mass. . .wonder what Nick is up to. . .
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

Sadly, I'm not quite that lucky. I pulled the hose from the turbo to the IC off and started it up. Same billowing clouds after a minute or so of idling.

Honestly, I'm not sure if there isn't any oil smoke in the mix...

I pulled the air filter off and drove around a bit after it warmed. Still seeing puffs of smoke behind me when I get on boost. Combined with the oil residue in the intake tract - I must be sucking *some* oil through the seals in the turbo.

Tomorrow I'm going to drive around a bit with the turbo hose pulled off and look for smoke. I want to at least narrow a few of the possibilities.

I'm wondering if oil could be getting sucked past the valve guides for my idle smoke screen issue. Anything is possible at this point.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

Eturbo924 · Joined: 09 Nov 2002 Posts: 2212 Location: Londonderry NH

Nick not that I know much about the turbo and this particular issue... but would it not make sence to clean it all out and then try to do the .... test outlined above? That way you are not sucking in oil that you had already done before you removed the air filter?

You are not having much luck with that car. Hmmm maybe I am not so sad that you beat me to it

Best of luck bud. I hope you find the problem soon and it is a simple fix. We all deserve one of those once in a while.

Eric
_________________
1982 924
1992 968
2003 C4S
Parts Parts Parts and More parts.
E-mail me for parts you need!
Drive Fast!

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Well, a long period of sitting is definately not great for valve seals. . .esp if they dry out before being run in.
_________________
Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Slam · Posted: Thu Oct 12, 2006 12:29 pm Post subject:

I'd suspect the head, like endwrench says. rasta's right about the valve stem seals - our 931 did what he describes. Lots of oil past stem seals till warmup. The oil leaks past while the car sits and the burns off as it warms up. But if your smoke is white, it's probably coolant. Taste it and see - coolant is sweet.
_________________
'88 944 Auto - may or may not resurrect

Eturbo924 · Joined: 09 Nov 2002 Posts: 2212 Location: Londonderry NH

Great idea you know coolant is highly poisonous right?

I normally go on smell. Coolant is more of a sweet smell when burning. Oil is not.

One other easy way to determine is is which fluid is the car consuming? Is the coolant slowing going down in the bottle or is the cars oil slowly going lower on the dip stick? Or both.

My friend with his 944 had some luck going with a thicker non-synthetic oil and using some no smoke once in a while.

Eric
_________________
1982 924
1992 968
2003 C4S
Parts Parts Parts and More parts.
E-mail me for parts you need!
Drive Fast!