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Join Date: Mar 2017
Location: Honolulu
Posts: 5
Oil Leak after Engine Reseal

Hello, all. I am in Honolulu, and I tackled with the guidance and assistance of an air cooled very experienced mechanic, a Complete Reseal on my 1990 C2 964. It had 48K miles, we did a compression check prior to strip down and all cylinders were ok. I had replaced gaskets and o rings to stop leaks at common offending areas, but the cylinder base gaskets on 2 cylinders were leaking badly. So, we tore down, but didn't split the case. The cylinders were clean, still had factory honing. I ended up with 2 broken lower stud bolts and the 2 base gaskets were broken. So, we cleaned everything up, resealed the gaskets with the green Viton and also the clear Molykote Dow Corning 111 compound to those base gaskets. After replacing all 24 stud bolts, and a 3 angle grind valve job, replaced exhaust side brass guides, teflon seals, put it all back together. I am experiencing still an oil leak from the base of 1 maybe 2 cylinders at those new base gaskets......??!!! We were super careful on re installation not to crimp or bugger them back into the case. I have the early heads without the top head gasket. We decided to keep it original, and it wasn't leaking from the heads before, only the base of cylinders. And that is what is still the issue, my heads are not leaking, just the base of 2 or 1 cylinders on drivers' side..

Does anyone have any recommendations on perhaps a stop to the offending leakers?!! Besides an engine out and re attempt!!!

I am planning on doing an oil change soon and remove and replace t
he oil line that goes from the oil tank, routes along lower rear part of engine and flexes and then up to the engine. That line got dented on the re install, so got a new one and will replace during the oil change.

Was wondering if anyone had tried to put in any stop leak for a gasket leak? I know its sort of sacrilegious to put in some foreign fix a leak crap in the oil, but I am willing to see if maybe there is some good German or Japanese product that in small form finds small areas that can try to stop oil from passing by? Anyone? Bueller?? I'm thinking to try Blue Devil....

Well, thanks in advance..

Alex in Hawaii Kai..

Old 08-15-2020, 03:03 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
lake wales fla
Join Date: Feb 2017
Posts: 599
Most likely not coming from the cyl. base o-rings but coming from the case thru bolt o- rings. This is a commonly overlooked reseal item on 964/993 engines and is very easy to misdiagnose as a leaking cyl. base o-ring. Unfortunately the only way to replace them is a full tear down to the case (again) and involves a special tool to install them. You do not have to remove the pistons but will have to remove the cyls.

One of my 993's has the same leak on the left bank near cyl. 1 and 2 and at some point in the future i will have to address this as the rest of the engine is dry. When you get down to the case remove the case bolts one at a time and replace the o-rings and torque them back down before going on to the next thru bolt. You will find that the o-rings are as brittle as potato chips.

As to your question about an "additive" let me share a quick story from years ago.

Customer comes in with a 944 turbo leaking from multiple areas and after an estimate was given he declined repairs. Fast forward 2 weeks later customer comes back complaning of no boost pressure (zero) and gives ok to diagnose. After some basic checks i pulled the air inlet boot off and the turbo shaft was locked up solid.

Long story short the customer had put in some Oil stop leak and it swelled the turbo feed line o-ring in the top of the upper balance shaft housing completely shut blocking off oil delivery to the turbo. The customer did not divulge this info until he was shown the swollen o-ring and the look on his face will always be in my minds eye.

My advice is while there are additives (snake oils) that can soften and swell old hardened seals and o-rings i would not put anything in your oil to try and stop the leak. Make sure you use Dow 111 on the case o-ring and bore because if you pinch or tear one you will have an even worse leak than just the old fried o-rings.

Good luck and keep us posted what you find

Old 08-16-2020, 05:23 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Join Date: Mar 2004
Location: Leesburg, Georgia, USA
Posts: 1,586
I will not put any stop leak to fix an oil leak.

Clean the area where it leaks oil, put a dye on the oil and drive it around.
You may be able to find the leak source and fix it the proper way.
1993 964 C2 still makes me smile
1996 318ti (280k miles) SOLD
2011 Silverado for hauling (32k miles) - SOLD
2018 Suburban Z71
Old 08-16-2020, 11:15 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Join Date: Oct 2013
Location: Prescott, AZ
Posts: 1,053
I second the no stop leak motion. Interestingly enough, I thought my 1990 964 was leaking from the case through bolt o-rings, but it was the cylinder base o-rings instead. For some reason, the cylinder o-rings were hard as a rock, but the through bolts o-rings were still pliable. But, in the OP's engine if the through bolt o-rings haven't been replaced, I would consider doing that. If the cylinder o-rings were adequately lubed when the cylinders were introduced into the case, it's hard to imagine how they could start leaking. The through bolts seems a logical place for a leak in the same general area.
1990 964 Coupe
1986 Carrera 3.2 Targa
Old 08-25-2020, 12:44 PM
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Metal Guru
911nut's Avatar
Join Date: May 2001
Location: Beverly Hills, Michigan
Posts: 2,524
Before you tear the engine down again, double check the triangle of death. It's easy to make a mistake on replacing the breather gasket or the breather hose could be bad.
Any leak from this area will mimic a cylinder leak.

Paul B.
'91 964 3.3 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, H&R Coilovers, ESB spring plates- 210 lb
Old 10-04-2020, 06:33 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)

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