White exhaust smoke at warm idle. Uh oh. What's the cause?

Eric86Red911 · 12:41 PM

I did a search and didn't see anything directly addressing this. If I drive around a bit then stop and idle, after a few minutes I start getting HUGE amounts of white smoke out the exhaust. Not every time, though. Within 2,000 miles it progressed from a litte bit to a really embarassing amount of smoke. Strangely, it doesn't smoke at startup or while driving.

My oil useage is around 1 qt per 500 to 600 highway miles, which I know is not great. On track days (120 miles) I'll burn 1 qt.

I recently turbo'd my car, so I don't think it's an oil overfill since I cut the line going from the oil tank to the intake manifold.

So is it valve guides? Perhaps a compression & leakdown is needed. Gotta admit, I'm nervous about this.

Porsche_monkey · 07-08-2008, 01:14 PM

I'd guess valve guides. Sorry.

Oil level is okay? Not too high?

burgermeister · burgermeister's Garage

You do have some sort of breather on the crankcase to replace the line from the oil tank to the intake, right?

Dixie · Dixie's Garage

Classic symptom of worn guides.

craigyirush · 07-08-2008, 04:39 PM

Don't mean to hijack but why would worn guides cause white smoke?
I thought worn guides caused oil burning and thus blue smoke . . .

vreference · 07-08-2008, 05:33 PM

Quote:

Originally Posted by craigyirush

Don't mean to hijack but why would worn guides cause white smoke?
I thought worn guides caused oil burning and thus blue smoke . . .

Also I thought it was pretty much agreed that valve guides were usually at fault for smoke that goes away when the engine is at operating temperature.

Traditionally white "smoke" (that looks like steam or water vapor) is attributed to water entering the combustion chamber... harder to do on a 911 though. A picture could help clear this up maybe.

vreference · 07-08-2008, 05:37 PM

Quote:

Originally Posted by Eric86Red911

I recently turbo'd my car, so I don't think it's an oil overfill since I cut the line going from the oil tank to the intake manifold.

Oh wow - didn't read this. All bets are off I would think. But smoke that increases as you idle the car could certainly be related to a turbo seal failure. Would be fairly quick to pull a section of intake plumbing after the turbo to check for oil. Also destroyed rings with the turbo but I can't think of any way that would lead to smoke increasing as you idle.

Eric86Red911 · 07-08-2008, 07:31 PM

Quote:

Originally Posted by burgermeister

You do have some sort of breather on the crankcase to replace the line from the oil tank to the intake, right?

Yup, put a breather on that oil tank line.

Quote:

Originally Posted by vreference

Would be fairly quick to pull a section of intake plumbing after the turbo to check for oil.

That just occurred to me too. I'll pull the turbo outlet pipes and see if there's any oil in them. Thanks.

DinFtown · 07-09-2008, 06:09 AM

Can you define sitting at idle??
Do you mean sitting at a stop light?
Sitting in the driveway with the E-brake on?
The reason I ask is white smoke is not oil, it is either water, but this only happens for the first 20-30 mins after the car has sat outside in humid weather for more then two days. The second cause is hydraulic fluid, in this case brake fluid getting burned. If it is brake fluid you will get white smoke moments after you but your foot on the brake peddle. This is the cause of a bad seal in your master cylinder, and your engine is sucking the brake fluid via your brake booster into the intake. I'm not saying this is your problem, but if the symptoms fit, then it is most likely.

DinFtown · 07-09-2008, 06:15 AM

More on that I just realized, is you will not have any white smoke while under boost because this would pressurized the brake booster, when the motor comes off boost it vacuums the brake boosted back down, this can beat on the seal in the front of your master since it would not be use to that abuse.
Do the symptoms fit??

Eric86Red911 · 06:45 AM

Quote:

Originally Posted by DinFtown

Can you define sitting at idle??
Do you mean sitting at a stop light?
Sitting in the driveway with the E-brake on?
The reason I ask is white smoke is not oil, it is either water, but this only happens for the first 20-30 mins after the car has sat outside in humid weather for more then two days. The second cause is hydraulic fluid, in this case brake fluid getting burned. If it is brake fluid you will get white smoke moments after you but your foot on the brake peddle. This is the cause of a bad seal in your master cylinder, and your engine is sucking the brake fluid via your brake booster into the intake. I'm not saying this is your problem, but if the symptoms fit, then it is most likely.

Wow, I NEVER would have thought of that. The smoke clouds have occured when in stop & go traffic, so yes, when braking. I haven't noticed any smoke when idling with the e-brake on. So you might be onto something!

And it has gotten a lot worse very quickly, too. Should be fairly easy to test; get warm, hold brake pedal down, and look for smoke. Or remove the vacuum line and look for fluid inside.

I'll let you know what I find. But the symptoms seem to fit. I should have smoke at startup if it were valve guides but that's not happening.

vreference · 07-09-2008, 11:04 AM

It has been known to happen! But a better way to test is probably just to keep and eye on your Brakefluid resivoir as it should not be changing much at all if nothing is wrong.

slw911SC · 07-09-2008, 11:57 AM

"vereference" Excellent diagnosis! This is exactly what happened to me years ago with a 77 S Coupe I had.

Eric86Red911 · 09:48 AM

vreference thanks for the diagnosis.

Brake fluid seemed to drop over a weekend trip & DE (700 miles), so that may be it.

But could it be the vacuum booster instead of master cylinder? I guess I don't understand the path the fluid took from the M/C to the engine intake.

tcar · 07-10-2008, 06:20 AM

Vacuum line from the vacuum booster to the intake manifold.

MC is leaking brake fluid into the booster.

DinFtown · 07-10-2008, 06:22 AM

Eric,
Its the master, the brake booster should be dry. Replace your master, and problem solved. You have a vacuum tube that runs from the booster attached to the master to the engine providing the vacuum power needed to make it easy to push your brakes in. The center shaft/piston section fits into the booster, and if the front seal in the master goes out, it will suck fluid into the booster, and thus it gains access to the engine intake via the long tube.

I'm glad I could help, keep me in mind if you ever put brakes on your 86
http://www.probraking.com/product_catalog.html

Dave

Eric86Red911 · 09:47 AM

Great, thanks again guys. New M/C is on order.

EDIT: new m/c did NOT help.

Turns out the oil tank breather was clogged so the oil tank was pressurizing, pushing oil into the turbos.

175K911 · 07-10-2008, 07:58 AM

Good thing that MC didn't fail while you were behind me on the track this weekend! Not that you were were ever behind me for long. except for the offie coming out of 1, but we won't talk about that.