Oil leak - rear main seal or oil pan gasket?

Maintenance/Repairs
1

I have a motor oil leak on a 1991 Chevrolet S10 pickup, 2WD, 2.8L, manual transmission.

The leak is around the bell housing area. The oil covers the bell housing and the transmission.

I think it is either the rear main seal or the back of the oil pan gasket. But how can I know for sure? It is difficult to see the back of the oil pan.

Would the oil INSIDE the bell housing be proof positive that it is the rear main seal? I have not looked inside yet.

Thanks.

2

Isn’t the bell housing above the oil pan rim?

3

I think it is both above and below.

4

Any oil leak will go all over the place underneath the engine b/c when you drive on the freeway there are 70-100 mph wind gusts blowing under the car through that area. That’s a good thing from the engine’s perspective as it provides some cooling to the oil pan. But not good from the point of view of spotting where an oil leak is coming from. It’s usually not possible to tell unless you clean everything up first, and then let it sit or maybe idle the car a while, then let it sit again. Sometimes you can find where the leak is originating that way. If you aren’t sure if it is oil or xmission fluid, or sometimes this helps to find where the leak is coming from esp if it is occurring higher up on the engine, a florescent die can be added and later the engine is viewed under a black light.

5

It is definitely motor oil, not transmission fluid.

Yeah, driving down the highway blows the oil all over the place, sometimes even up and forward, which is counter intuitive.

Would motor oil from a source other than rear main seal be able to get inside the bell housing?

6

I would think if the very rear of the oil pan gasket was leaking, it would make a mess in the bell housing

7

Look for your oil pressure sending unit and see if it is leaking. Also check your valve cover gaskets.

8

Check the valve covers. If the entire bell housing is covered in oil the leak is somewhere up high, and valve cover gaskets are far and away the most likely place to leak.

9

You might be able to trace the path backwards using a UV sensitive dye additive and a blacklight, available at any parts store.

10

Mike, the 2.8 V6 is known for rear main seal leaks. I had one in 1983, 5 rear main seals were replaced under warranty and each time, 2 weeks later, they were leaking again. 85% chance that’s what it is. Pull the transmission and bellhousing, If its oily in there, replace the seal and inspect the clutch disk, it will be ruined by the oil if you get even small amounts on the facing.