Mystery oil leak

Tom Hoczyk

Tom Hoczyk

PCS Past President
My '60 Eureka, 390 engine, never leaked any oil until coming out of a service shop in which the drive shaft was removed for rebalancing. The car was primarily there for having some brake work done. My transmission shop, who I know well and trust, says it's not likely that removing the drive shaft would be the cause of a rear main oil seal leak, and I believe that. The leak actually started almost two years ago, before the car was repainted. But after repainting, of course, the leak still occurred.

Characteristics of the leak: It would only seem to leak after the oil was warmed up after driving, and not be a continuous leak, rather one that would stop after a while, but not after putting quite a spot on my driveway.

Current problem: I just got the car back yesterday from the transmission shop, which installed a new rear main oil seal. It was a split seal, not a rope seal, and the transmission did not have to be removed to do the job. But the oil leak is still there, actually somewhat worse than before. It appears to drip from the weep hole that is designed into the transmission bell housing. That's what made me think "rear main". I'm incredibly disappointed that the new seal didn't stop the leak. Am I missing something? HELP! Tom
 
I would check the oil sending unit. On the Criterion it had quite a leak and all thoughts were it was the rear main seal. As it turns out, the oil sending unit on mine was mounted high up on the rear of the block so as it leaked it gave every appearance it was the seal. I had the same thing happen to another old Caddy hearse I owned years ago.
 
Make sure you check what kind of oil it is. Engine oil or transmission fluid?? The bottom hole in the torque converter cover can drip from the rear main engine seal or the tranny front seal. Very basic, but worth checking......

Thanks,
Mike
 
Mike, the engine oil prior to the seal being changed out was dark, as was the color of the leak. They had to drop the oil pan and I instructed them to install new oil, and the current leak is golden oil yellow, so I doubt it's transmission fluid.

Richard, I'll definitely check that sending unit. Thanks to both of you! Tom
 
I have rebuilt three different 390s so far of course with hydramatics from oldsmobiles of past, which your car has, (they were all passanger cars),and one thing that was noticed from the machine shop on one was that the transmission can actually push the whole Torus forward (due to one of the many clips holding the torus together being broke/bent/missing) causing the crank to be pushed forward. I dont know what the quick fix could be or if yours needs a possible rebuild.
too much trans oil pressure pushing everything, or something is not tightend down enough. just my experience with 390s and the problem you stated.
 
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