Lets talk about rear main seals again.

[casadejohnson]

I recently replaced my rear main while I had the engine out in my 74 ( 351w ). Here is a thread I had when I did it. http://classicbroncos.com/forums/showthread.php?t=202515
It would appear that it is still leaking and its probably worse than before in some ways. Previously, it had the annoying drip on the garage floor. Now I still get oil on the garage floor but it is the worst right after I start it. If i start it up and back it into the driveway to warm up for a bit it will leak bad for several minutes but it will get much better after it gets up to temperature. After I put the engine back in, it didn't leak at all the first few times I ran it then it got progressively worse. Obviously, I'm not very excited to do this a second time. Maybe my leak is someplace other than the rear main but the oils is definitely coming down between the block and the bell housing.
Suggestions?

 

[ransil]

What oil pan are you using?
if you used a newer blue silicone gasket with the Bronco oil pan that was my issue,I switched to the mustang 5.0L oil pans and no more leaks. this was after 2 or 3 rear main seals.

 

[demesauce]

Use lots of black RV silicon

 

[patterdale]

It could be the rear pan rubber. Instead of lots of any kind of sealer figure out why a gasket that is supposed to do the job without sealer isn't doing what it is supposed to. A little rtv in the corners between the cork and rubber like with the intake gaskets is all that should be needed.

 

[Broncobowsher]

How well is the PCV system working? If the vent side of the PCV is to restrictive then you can build crankcase pressure and push past the seal. Lost a rear main on a 5.0 because I didn't let the vent breath enough. Upped the vent size and it didn't kill any more rear main seals.

I do not go with the lots of RTV fix either. Less is more and in just the right spots. That post of the first fix looks like everything is spot on. 2-piece seal, lip toward the inside, ends slightly offset , anarobic on the corners of the cap. All the right stuff. Are you sure it is the rear main, not valve covers drooling down? I have seen a lot of rear mains blamed on bad valve covers.

 

[casadejohnson]

How well is the PCV system working? If the vent side of the PCV is to restrictive then you can build crankcase pressure and push past the seal. Lost a rear main on a 5.0 because I didn't let the vent breath enough. Upped the vent size and it didn't kill any more rear main seals.

I do not go with the lots of RTV fix either. Less is more and in just the right spots. That post of the first fix looks like everything is spot on. 2-piece seal, lip toward the inside, ends slightly offset , anarobic on the corners of the cap. All the right stuff. Are you sure it is the rear main, not valve covers drooling down? I have seen a lot of rear mains blamed on bad valve covers.

I believe the PCV is in order, its got a new valve hoses and even the basket filter thing that keeps oil from sucking up the PCV valve. I'll check the valve cover gaskets again but they are also new rubber gaskets and I have the mustang cast aluminum valve covers so they don't bend up like the stamped ones. I'll check it out just the same.

 

[Broncobowsher]

I believe the PCV is in order, its got a new valve hoses and even the basket filter thing that keeps oil from sucking up the PCV valve. I'll check the valve cover gaskets again but they are also new rubber gaskets and I have the mustang cast aluminum valve covers so they don't bend up like the stamped ones. I'll check it out just the same.

That sounds like you have EEC EFI. This raises my suspesion even more. The vent hose at the oil filler neck to the intake duct between the MAF and the throttle body, that tends to be undersized. I had to open mine up a couple sizes to keep the rear main from leaking

I am now very curious about the fresh air side of your PCV system.

 

[casadejohnson]

That sounds like you have EEC EFI. This raises my suspesion even more. The vent hose at the oil filler neck to the intake duct between the MAF and the throttle body, that tends to be undersized. I had to open mine up a couple sizes to keep the rear main from leaking

I am now very curious about the fresh air side of your PCV system.

You are correct, 93 Mustang EFI. Did you just increase the vent hose size itself or did you use larger hose fittings as well? What are you thinking about the fresh air side? What should I be looking for?

 

[Broncobowsher]

I actually increased the fitting size. I went crazy and went from 3/8" to 3/4". Mostly because that was the parts I had on hand. I did a bit of research to find that the mustang crowd was having issues with the little hose not allowing enough flow and causing a pressure build up. Never had an issue after upping the vent size.