Ian928

Guys,

I am posting here also, even if the question is not about 928 but my wifes 951, hope it is all right!

The case: She has been loosing coolant for some time, we have bought a new set of hoses and was waiting for the right time to swap them. Then she realised that the car was smoking white more and more, and she started loosing cooling water faster. Also, the car started running rough. We checked the plugs, and altough we could not see anything special, and that all 4 looked the same, we changed them and the car then ran fine again. We removed the plugs yesterday to check condition and took a picture. I would have suspected one of the plugs to be clean, but this is not the case here. Or is possibly the tip of plug no 2 a giveaway? What do you think? These plugs are colder than standard and the car has not been driven hard so that is possibly the reason for the carbon build-up.

Charley B

Time for a compression test. Possibly a cracked head.

Ian928

Thank you Charley! I will try that today! So you consider that one of those plugs is coming from a cylinder with a coolant leak?

The reason I am asking is I have a hunch that it may be a cracked turbo and that the water is not going through the head. When she pulls off after idling for a while, there is a cloud of white smoke, my theory is that water leaking into the exhaust from the turbo is staying in liquid form and accumulating in the muffler. When she increase throttle the water is getting blown up into the pipe and comes out as white smoke.

tmpusfugit

Generally if a head gasket is leaking water into a cylinder the plug will be "steam cleaned" and will look very clean as a result.....I would not expect all of them to look as do those in the photo....

MainePorsche

+1

AO

I agree with the posts above having experience a HG failure myself. Here is what mine looked like. In my case it was cyl #7 that went. It's the one that looks a bit wet.

I would say your plugs look either oil fouled or you're running quite rich. Hard to say for sure.

If you suspect a HG leak, there are only two places for it to go. Either into the oil or in to the combustion chamber and out the tail pipe. Is there a big white cloud upon startup? Is there any "milkshake" in the oil?

Ian928

No oil in the water at all, no water under the car, LOTS of white smoke from the tail pipe.

I am leaning towards cracked turbo housing or craked head leading into the exhaust port...

GlenL

When?

Head gasket failures are characterized by steam on start-up and boiling over in operation.

A clear test is to run it up to temp and let it cool. Then remove the plugs and crank it. If there's a head gasket the water will have been squirted into the cylinders and when cranking it'll fly out of the plug holes.

I've used this several times to overcome that denial regarding "it just can't be the head gasket again."

Lizard928

Those plugs look oil fouled for sure.
No signs of HG failure on them.

However lots of white smoke out exhaust is classic HG failure. BUT the exhaust can have tons of white smoke just from condensation in the morning. Does it still have white smoke once it is warm?

However from those plugs, I would be inspecting the turbo seals, and the valve stem seals.

AO

+1

When you shut down a fully warm engine, the coolant system is still pressurized and if there is a HG leak, the coolant will leak into the cylinder (or oil passage). When I pulled the plugs and cranked the engine, coolant came out of #7. To be sure, I would lay some paper towels across the open plug so any coolant that might be forced out will show up on the paper towel.

WallyP

Water in the cylinder will clean plugs.

Coolant in the cylinder will often leave a hard gray deposit on the plug from the ethylene glycol. Number two might qualify...

Ian928

Thank you all!

Here are some more details:

Car has done 175K miles on what we believe is the original turbo and HG
The car is smoking white all the time, but in rush hour after idling for some time and pulling off there will be a huge white cloud
The smoking and coolant loss has evolved, it is severe now and the car will start to overheat because of low coolant level after a short drive
There is no bubbling in the coolant tank (as we can observe)

I am thinking it can not leak into the chamber at that rate and not affect one of the plugs more... On the 951-forum i found reference from a guy who has had similar white smoke symptoms and changed the HG only to find it was the water cooled turbo that was leaking into exhaust. Apparently, this means the tubine housing must be cracked, because the coolant is going in internal waterways inside the cast housing.

I will try to pinch the three coolant hoses going to the turbo and see if that changes the symptoms.

JakeS2

- Turbo leaking oil to intake manifold
or
- Cylinders too worn out and oil gets into combustion chambers

If you suspect water/oil mixuter in our cars, stop driving immediately. Hydrolock is known to tear holes into the aluminium block...

Ian928

An update: We pinched the hoses to the turbo and went for a drive. There is NO white smoke and no water loss as far as I can see! I will double check by removing the grips to let water to the turbo again, but I am pretty sure the Turbo is going out and the HG stays in for now.

Ian928

We removed the clamps and it seems the wite smoke is back again. It did not smoke on startup, but started smoking when idling for a little while.

Also, we removed the plugs again, put som paper over the openings and cranked the engine. There was no staining on the paper from water. Afterwards I checked the pressure by loosening the cap on the header tank and it did still hold a lot of pressure.

Regarding the comments about the plugs, here is a picture of them after a trip with some more throttle applied: