Dan87951

Last Friday I went up to Grand Rapids to pick the car up as the owner of German Auto Service said my car would be done today. Well we drive up there and they are still working on it. About an hour later he said they road tested it and still found oil leaks. He showed us the oil leaks, it was a very slow drip.........drip, it had practically stopped by the time we got to look at it as the car had not been ran hard until a few minutes ago. Yes the replaced the rear main seal with a oem one. He offers to take apart the car again free charge to diagnose. So we drove home that day without the car. Well today I get a call from the mechanic today and he tells me the reason why my car was leaking oil was because of my boost pressure. He said the did serveral tests while driving the car with and without the oil cap. He told me when the oil cap was off it would releave the pressure inside and not cause the rear main seal to leak. But when the car was driven hard with the oil cap on it would leak out of the rear main seal. I have boost gauge and proceed to ask how much boost I was running. Up around 19psi he says. I WAS SHOCKED! Howard Cooper must have been playing around with my boost controller I guess?? I normally keep it around 15psi. My question is would 19psi of boost cause my rear main seal to have a small oil leak when driven hard? How do you guys running insane boost levels keep your seals intact?? Is there some pressure relief system I'm not aware of? I'm afraid to even run 15psi of boost now because anything over factory boost will cause it to leak he said. I will be picking up the car tomorrow are there any questions I should ask him in particular?

Dan

tecart

if the rear main seal is bad, it will leak at any boost levels and even at idle, the rear main seal must be put in correctly, all the way in its bore with a special porsche only tool, this is a must to prevent leaks, also high boost levels like 20 -24 psi dont help rear main seals over the long run but if you install it right no boosting of 20 psi will make it come out and start to leak, if after install the seal is leak free at any boost level you are ok, many people install the seal wrong/ not in far enough and that is a problem too some even use loctite 574 here as an extra precaution to never leak, i hope he installed the seal right but it sounds like he is bs ing you hard, the seal dont leak due to an oil cap on or off, if its bad it will leak at idle and on boost and at 10,15,20,25 psi, the seal needs to be redone again if it leaks onto the crossover pipe iun the middle of it, test it at idle and youll see it leak for sure, trust me 100%

951and944S

Dan, think of your crankase, the bottom of your engine assembly as a box, where the crankshaft is contained.
The crankshaft's rotation causes offset journals to push up and lower (crank) the pistons via the connecting rods. The pistons are sealed to the cylinder wall with piston rings.

lol patience...

Incomming air and fuel are compressed when the piston travels upward like an air compressor.

This compression is separated from the bottom crankcase "box" by the compression rings of the piston.
When you get compression crossing the rings into the domain of the crankcase, the crankcase pressure becomes high enough to blow out even a properly installed seal.

So, either you have other issues, like damaged rings, or a worn cylinder wall, possibly even compression from atop the piston crossing into the oil drainback passage at a blown spot on the head gasket.

If you feel these guys were competent in the repair, you really can't blame them.
Ask if they will do a compression/leakdown test to prove that it's not their fault.
The reason you are getting more leaking with increase in boost, is more cylinder pressure will cause more compressed air/fuel to bypass the rings/piston/headgasket, whichever the fault may be.
The only other cause I can think of would be the turbo is internaly (center section) passing boost to the oiling system, but the oil pressure would be pegged, thus the oil can't drain back into the pan fast enough through the rear main seal drainback, and it's pushing the seal out.
You could mount a threaded atmospheric, filtered vent to the cam housing on one of the allen bolt access hole plugs and temporarily patch the problem, but it's really something more serious.

Email me if you want....
you've got the address

Terry

JonM..

The crankcase is ventilated to the intake boot which is a constant source of vacuum, so I can't imagine boost being a source of the problem. However as said above you could have tremendous blow by, in which case you have bigger concerns than oil leaks.

Bri Bro

I was think the same thing, if crankcase preasure was great enough to cause and oil leak, all the oils sealing gasket would be in trouble, front, pan, rear etc.

My guess is that it IS leaking all the time but running it under boost makes it worse. Sounds like a problem that will just get worse with time.