MXHowes

Of course oil leaks on the 30v are very common and most fixes require major surgery. Since I'm about 20K away from a Timing Belt Job the Valve cover and cam gaskets/seals will have to wait for awhile. But the Oil cap leak has baffled me. I tried a new gasket which didn't help, then a new cap/gasket with the same results. After digging thru the archives I found a lot of people blamed the PVC system for building up pressure and causing the leak. I eliminated the possibility of crankcase pressure thru a quick test by removing the oil cap and putting a latex glove over the rim of the fill hole. At idle the glove would fill up a little but not enough to inflate the fingers, at 2K RPM the glove was sucked back into the fill hole. I knew that back pressure was not the cause of the leak. Somehow the oil had to be leaking past the gasket. A very close inspection of the gasket mating surface showed a lot of small casting flaws in the valve cover surface, this area should have been machined from the factory but is not. THE FIX was to get more pressure on the gasket. I was not able to put two gaskets on my stock oil cap but I cut a new gasket out of some .030" material and added it to the cap side under the rubber gasket and wow! no more leaks! I also have a smaller diameter cap (I think it is a diesel) that I use just because it looks better with the engine covers off. This cap took two gaskets and works fine. Another thing you can do for a quick test is to only put the cap 1/2 way on, leaving it at it's hardest spot just before it rotates into it's final 'locked' spot. This will also apply more pressure to the gasket.

Hope this works for you.

4Rings::G2 boosted::

usually this is due to your pcv not working correctly, but on extreme occasions could also be due to increased blow-by of the pistons due to wear. First, replace all the pcv hoses and valves with new ones, you can get them from ECS. After that, if the problem continues do a leak-down and compression test. There should be no reason for double gaskets.

4Rings::G2 boosted::

while idling or revving in neutral the engine has no load on it and therefore there will be little to no blowby from the pistons. It's not until you drive the car and put load on the engine that blowby happens and pressure builds up inside the block.

MXHowes

I've pondered the oil leak issue quite awhile now and here are few observations maybe you can enlighten me on.......

1. If what you are saying is true 'only pressure buildup' causes a cap to leak, then with a properly working PVC system you should not even need a gasket, there should always be negative pressure in the block and the gasket is only there to prevent outside air from entering the system, therefore "a cracked, broken, missing or leaking gasket" would not be the cause of the oil leak.

2. Why is there a need for a PVC hose on the both valve covers? Should not the pressure be equalized thru the oil return holes and only one hose required?

3. If question #2 is true then why would your oil cap leak if the PVC Hose from the right bank is cracked & broken (this should relieve ANY pressure buildup)

I'm just trying to be logical to help understand the problem.

4Rings::G2 boosted::

the gasket is there more to prevent dirt from entering then to prevent oil from coming out.

The oil return holes do fill up with oil under high rpms, so air cannot easily travel thru them.

Not sure I understand your last question, are you saying that the driver's side pcv hose is broken (open), yet the oil is still leaking out of the oil cap? A broken hose should indeed relieve the pressure on that side of the engine, unless the engine is worn to the point that it's blowing by more then the hose can relieve. I can tell you from experience that with zero compression on cyl #5 my engine was spraying oil out of the cap everywhere, on the hood liner, on the exhaust, the whole engine bay was soaked on that side. It was doing that even though the pcv system was fully functional There is only so much pressure that the pcv can relieve.

MXHowes

If pressure is relieved thru the cap does it do this by overcoming the spring on gasket force or thru some internal relief built into the cap. Taking a close look (without tearing the cap apart) shows two part construction which leaves the possibility of oil vapors going around the gasket.
Anyway, right now I stopped the oil leak with a thicker gasket and it is working. I do have a new PVC hose and suction pump to install when I get around to it. Maybe I will put this discussion on hold until the new parts are installed, go back to one gasket and see what happens. I can always do a compression/leak down test to eliminate that aspect but the engine does run perfect and has always been babied. I don't think (and hope) that major wear is the problem.

audix

One thing I noticed, while I was working on my car, one of the oil return hoses (ones that connect to the valve covers) broke. Inside, there was a clog blocking any oil flow back to the engine oil pan. I would think, this would cause the oil pressure build up.

4Rings::G2 boosted::

it is designed however to seal the valvetrain from dirty air getting in when under vacuum conditions. If the PCV system is working correctly and the engine is healthy there should never be any positive pressure inside the head, it should be either neutral or negative at all times.