Help with Oil Leak


Please help me figure out my oil leak. I had to skip my last run at my last HPDE due to an engine oil leak…lost between 1/2 and 3/4 of a quart in one 25 minute session. The leak seems much more pronounced under heavy loads since the car didn’t leak much on my 1.5 hour drive home from the Summit.

The leak is at the bottom of the bell housing on the transmission and drips pretty heavily when the car is driven hard. I pulled the inspection plate on the transmission, but wasn’t able to tell if it was coming from the oil pan gasket or the rear main seal.

FYI, I replaced the oil pan gasket about two years ago. I also replaced the clutch and rear main seal (RMS). After replacing the RMS, I noticed an oil leak from the bellhousing. Went back and did the RMS again and haven’t had a problem until now. Not sure if it matters, but I bottomed out the car going over a pothole a few weeks before the HPDE. However, I do have a heavy duty skid plate installed.

Any suggestions on diagnosing the oil leak? Also, I’ve read that there are two types of RMS. I have a rebuilt engine. Could it be possible that I installed the RMS? Thanks.


Check your oil pan bolts for tightness and your valve cover gasket/bolts. If the RMS was installed properly, it’s unlikely to fail. Hitting your pan on the ground makes me think something is wrong with the pan.


FishMan wrote:

Thanks. I’ll give that a shot and will probably just replace the oil pan gasket first…I really don’t want to pull the transmission again.


If your replace the gasket, the preferred gasket is the red paper one. It’s available from Bimmerworld for $6.99; it’s the type 2 gasket. Do you have a scraper? Regardless, make sure everything is clean and oil free and coat the gasket with Permatex or Loctite Ultra Gray on both sides before installing. Underneath your valve cover, don’t forget the 4 rubber plugs that are aligned with the rocker shafts (2 aft and 2 forward). Coating the underside of them with Ultra Gray helps also. Good luck!


That’s a helova oil leak. As a last ditch effort before getting in deep, clean the engine and tranny carefully. Try to also clean the engine block towards the top of the tranny and also the back of the head. Yes, those are hard to get to, but if it’s coming out of something around the back of the head, that might fool a person into thinking it was coming out of the back of the block.

Then put the car up on jackstands, remove the flywheel access plate and run the engine for a bit. Get under it while it’s running and watch closely for the oil to come out. The result of this could be bad news, but hopefully you’ll be able to pinpoint where the leak is.

Ranger’s heirarchy of suckage:
Knowing what the problem is, and it’s not bad.
Knowing what the problem is, and it’s pretty bad.
Not knowing WTF the problem is.


I thought this was implied, but Fish’s order of problem solving:

  1. Identify the problem
  2. Fix the problem

If 2 seems impossible, go to bed…


FishMan wrote:

No, I don’t have a scraper. Should I add one while doing the gasket?


I guess its worth a shot on cleaning and reinspecting, but I had access to a lift during the first inspection and everything looked clean around the top of the transmission.



Before you do anything, make sure you have a good idea where the leak is. Take Ranger’s advice… If you plan on racing with this engine, it would be a good idea to consider a baffle/scraper if you have your pan off.


Re. top of the transmission. Sounds like you can rule that out.

Re. scraper. I put some info in Resources the other day. There’s no use me blowing up engines if others can’t learn from my fiasco’s.