Rear main or oil pan leak?
 

I've got a leak coming off the center of my bellhousing. It only seems to leak when the car is NOT running, no signs of oil being slung around inside the bellhousing.

How much lower is the oil pan gasket along the rear lip than the rear main? I'm almost thinking that, when the engine is running, the oil level in the pan is below that rear lip and the pan can't leak, but when I shut the engine off and the oil drains back into the pan, the oil level is higher than that rear lip and that is where my leak is. Is that a sensible theory?

The oil level in the sump is quite a ways below the rear main seal and pan gasket.

Your crankshaft isn’t turning in a bath of oil, it sits above the oil level.

Your main seal is leaking oil that’s inside the oil passages after shutdown. Sitting there static it leaks whereas when it’s running the main seal will seal up.

If I don't start my car for three months, the puddle keeps getting bigger. Given that the rear main is higher than the oil pan seal, how is this possible?

It's a Milodon 7 quart pan, if that changes anything. You are saying if the car is sitting and I loosen all of the oil pan bolts one full turn, then nothing should come out of the pan if it is filled to capacity? Even considering that the engine is tilted to the rear a bit?

Have you ever filled an oil pan with 5 quarts of oil with the pan sitting on the garage floor?

The oil level doesn’t even come close to the pan gasket. Again your crankshaft doesn’t sit there half submerged in oil.

How big around is the oil puddle after sitting for 3 months?

maybe 6 inches in diameter?

Doesn’t sound too bad for sitting that long. What main seal are you using?

I'm not sure, been awhile since I had the engine put together. It's an IA2 block too, some of which I think had some issue with the rear main not sealing properly. I have no idea whether my block has that issue.

I'll keep playing with it. I noticed the drain plug is leaking some too, so I'll fix that first. I don't think it is wicking all the way to the center of the pan to form a separate puddle, but anything is possible.

I also had a dipstick leak at one point, thought I had that fixed but better check again.

I'm trying to think of something stupid but funny to say but coming up with nothing.

maybe try one of the oil dye detection kits?
worked GREAT for me when i had an issue. drips, that sounded so similar to yours, but mine was actually from an aftermarket oil breather that leaked oil and would run in places hardly visible to see
wasn't until the dye test that showed the culprit.
since you have a larger pan, you may need two bottles of it
might pin point the exact location.
also, i know it may sound real stupid, but are you sure it is oil? not PS fluid or brake fluid?
one other issue i had that made me think was oil leak, was actually the mater cyl leaking a little and it would traverse all over the place and get the back of the pan and drip, found that one when i opened the master cy and notice low fluid and replaced the seal, all was well
that leak went away
just some odd ball outside the box lessons learned to pass on

Then you're not trying hard enough! We all know you can do better ....

I tried the oil dye stuff, it does work. It's just hard to get under there and see much. I probably need to stop being lazy and put it up on jack stands so I can get a good look.

I know I have posted this before, but will again. Pontiac engines are almost as famous as Harley Motorcycles for leaking oil. Back of the engine is just terrible to seal up. PMD knew this from day 1, so over the 25 years they tried to crutch the deal with some Band Aids. Pan corner reinforcements, 3 different pan rear seal designs along with modified pans. Never really solved 100%. The only method I have found that is 100% foolproof for diagnosis is to use a smoke machine and fill the engine with harmless white smoke. Then you know for sure where the leak is. Very difficult to diagnose a leak from the rear pan, rear main seal or split line between block and rear main cap. All three areas are big leakers. Smoke machines available everywhere on the internet usually under the title "evap. emissions smoke tester." Good luck with the repair.

It sounds like it could be a leak from one of the welds for the sump.

+1 to the smoke tester. It made it super clear almost instantly where my leak was coming from.

I assume the flexplate/flywheel has to be removed to see the difference between pan gasket and RMS? I need to diagnose one on my 64...

I didn’t remove the flexplate and tested the engine installed. That said, I had a pretty bad leak.

Pic of the leak: https://forums.maxperformanceinc.com...4&postcount=87

Thanks

I pulled my motor 2x in the last 2 weeks looking to fix what I thought was a pan leak mostly at highway speeds.
So I folded a strip of paper towel over a 1" scraper and was able to get it placed in the gap behind the flywheel, above the pan seal. I put a few of these in around the flywheel .
Next I "pressurized" the crankcase by plugging the PVR and blowing air into the breather hole using a shopvac for a few seconds.
Pulled out the paper towels, and sure enough there was an oil stain... well above the pan lip.
...now waiting on graphite rope seal delivery and pulling motor for the 3rd time.

op here ... we adopted a four yr old alaskan malamute last week ... completely insane ... my life will never be the same ... oil leaks are the least of my concerns ... dear god please help ... HELP!!!

I feel your pain!!!
We got a 4 month old Cocker Spaniel that has taken over the house! Cars have taken a back seat for now!