Oil in R154 bell housing

KpSupra

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Had my engine rebuilt and have only run it 500 miles. I found a good bit of (dark) oil in the bottom of the bell housing, so I took it back and told them it had a rear main seal leak. They looked, but there is no oil on the flywheel or clutch cover, so they suspect it is running down from the outside and leaking in.

It's a good possibility, but I only have two small leaks up front and the engine around those areas are still clean. I suspect it is coming from the rear of the engine, although we found no oil running down the back. I am also wondering if it leaks only when boosting. Any ideas where it would be leaking from?
 

GrimJack

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There are only four things that can leak at the back of the engine. In order of probability:
1. Rear main oil seal
2. Valve cover gaskets
3. Rear main plate gasket
4. Head gasket

If you are missing the bottom bell housing shield, it's possible that high speed runs are causing oil from the underside of the engine to fly into the bellhousing.

Are you certain that it isn't transmission oil?
 

pogoism9

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boosting puts load on the motor, which in turn loads the trans. As far as i know, there is a front seal in the trans. If this is shot, guess what you get?

I'm gonna go with GrimJack here, Are you certain that it isn't transmission oil?

Makes sense considering you said there was no oil on the flywheel/clutch cover.
 

7MGTEsup

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Could also be the rear of your sump leaking and dripping down into the bell housing.
 

MK3Brent

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Rear seal, me thinks.

Wait to see if the clutch starts slipping, then show that to your mechanics. :)
 

QWIKSTRIKE

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Check the rear seal or see if the oil pan is loose in the rear or some where along the sides. A loose oil pan and no cover and a moving car can cause this to have oil in the tranny. The valve cover screws may be loose as well.
 
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KpSupra

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I'm sure it is not gear oil. That stuff smells so bad you can't hardly mistake it. I'm thinking it's probably running down the back of the engine. I think there are two cover plates that cover holes on the back of the engine. I was under the impression that they were vacuum orifices, which I plugged with a piece of machined 1/8" plate and used RTV for the gasket. I will get him to feel the back of the engine under those block off plates and see, but aren't these vacuum orifices?
 

supraguy@aol

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Sounds like you're talking about the EGR holes in the back of the cylinder head. No oil would come from those. Is the outside of the bellhoising getting oily? If not, I'm going to agree with the above; it might be your real main seal.
 

KpSupra

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Sounds like you're talking about the EGR holes in the back of the cylinder head. No oil would come from those. Is the outside of the bellhoising getting oily? If not, I'm going to agree with the above; it might be your real main seal.
Yes, there is some leaking down on the passenger side and it looks like it could be getting in, but it doesn't look like near the amount that is in the bottom of the bell housing. We have been checking the back of the engine but I needed to know where to look.

With the car on the rack, the front inspection plate off and the engine running, we could not see oil dripping down under the rear main area. I had thought about the fact that the oil would sling off the flywheel, and it could be that it only leaks under boost. The mechanic was going to clean the oil off and drive it under boost and come back and check. Hopefully he can find it.