Bob Rouleau

My pal has a 993 TT. It blows oil when he hits boost. Turbos removed and inspected - all ok. Crankcase valve replaced. Leakdown and compression tests are fine. Could the oil rings be stuck? If so, any way to unstick them without taking the engine to pieces? Oh, one other thing, when driven on boost the dip stick is blown out of the tube!

Stewart

Wrong oil filters are the most likely culprit - well documented on this forum.

Quadcammer

Disagree.

Filter issues typical show up as smoking on cold start up, not while under boost.

Bob,

Some strange stuff here. On a typical wet sump engine, blowing the dipstick out is an indication of excessive blow by. I guess its possible that blowby would go through the case to the oil pump, oil lines, and into the tank thereby blowing the dipstick out, but that would almost definitely show up in compression/leak down.

When you say compression and leakdown are "fine", what do yo mean? What are the actual figures.

have you used a boroscope on the cylinders?

Bob Rouleau

I haven't got the numbers, but the dealer says the leakdown and compression numbers are fine. It seems like blow-by. Dunno about the borescope - sounds like a good idea.

The blowby only happens when on boost otherwise all is normal. NO smoke at startup. On boost .. lots of smoke.

ca993twin

My "guess" (its less than a guess) is that the oil tank itself is getting pressurized by the engine boost. How else can that dip stick get blown out? How this might be possible I have no idea. Can excessive pressure in the sump get transferred to the tank? Be sure to let us all know how this gets resolved.

Basal Skull

+1

Dumping oil only when on boost I would think must be from the turbos. Even if the seals are okay, if there is blow by and pressurized crank case I think it can probably cause some back pressure in the oil return lines to leak through the seals. I assume it's from both tail pipes - so both turbos (which would be less likely to go bad at once) or more of a general thing affecting both sides? Can one even get 'intermittant' blow by? There's also a pump for the turbo oil return line incorporated in the alternator bracket that might be bad that has trouble keeping up at higher/boost rpms?

Bob Rouleau

Smoke (lots) comes from both exhausts. Lots accumulates in the intakes as well as you'd expect. Turbos were changed so it isn't them. Hard to imagine bad oil rings (bottom ring on the piston) while compression and leak-down tests are fine.

UserA

Proverbial shot in the dark, but could it be that the diverter valve in combination with the ECU not cutting boost and fuel on its failure? Does your friend have an aftermarket chip?

OverBoosted28

If boost was the cause of this "blow by" in the oil system, you would have alot of other leaks other than the dipstick getting pushed out. Can't even see how boost pressure in the intake system could make this happen in the oil system before other problems arise. These cars can't be chipped. The DME ECU has to be remapped.

XR4Tim

Excessive pressure in the tank. Are the breather hoses kinked or plugged? There is a check valve at the top of the oil tank, but I'm not sure what it does.

Basal Skull

By oil in the intake, do you mean from the breather/air box before the turbos or just in the intercooler/ hoses. If just on the intercooler /hoses then it has to be from the turbos, whether they are good or not.

Basal Skull

If the turbos are good and you think the rings are good then I'd look at the turbo sump return pump as I mentioned previously as that would also affect both sides...

Steve Weiner-Rennsport Systems

Bob,

Leakdowns are not always conclusive; they do not always show broken rings. In many cases the values are OK, but they are still sealing well enough to give decent numbers.

I wouldn't rule out ring/piston issues quite yet.

Felix

I'm struggling a bit that it could be the rings - wouldn't cylinder pressures off boost be only slightly less than on boost? Thus boost would only slightly worsen the issue?

Did this problem start all of a sudden or has it appeared gradually?

Bob Rouleau

The problem started suddenly. No chip the ecu is stock. Guys, thanks for the advice and input. I guess a tear-down is the only solution.

Best,