Hi guys and gals. I need some help pinpointing an oil leak on my '90 F250 with a 351. I have already replaced a leaky valve cover gasket. I am now trying to figure out if my leak is from the oil pan gasket or the rear main seal. If I remove the rubber seal on the bottom of transmission bellhousing there is a very very very small amount of oil in there. The oil leak is a pretty large one though. If the rear main seal were leaking that much, wouldn't there be a whole lot of oil inside the bellhousing?

Thanks for the insight,
Hunter

 

Do you see the oil dripping from the outside of the bellhousing as well? Pretty much anything in that area is most likely going to be your rear main, its the only way that oil is going to get in there.

-Chris

 

Thanks for the reply Skan. Basically, the entire underside of the truck is covered in oil. The bellhousing is heavily coated on the outside, but I think it must be something else because there is even oil on the frame rails, starter, oil pan, pretty much everywhere.

Is there any way that from all of that oil a small amount got into the bellhousing?

Thanks,
Hunter

 

Its possible, It could also be both...leaking ever so slightly from the rear main seal AND the back of the oil pan gasket. I vote for the pan gasket.

 

Thanks Brian. I just cleaned the pan and drove down the highway. Sure enough, the pan gasket is leaking. I was planning on doing this myself, but my mechanic quoted me $450 to do it which invloved dropping the transmission. I might just have him do it so he can put in a new rear main seal while he has the transmission out.

Thanks,
Hunter

 

Good call, wouldn't be a very fun job. $450 ain't too shabby if you can get him to toss in the rear main labor for a little extra.

-Chris

 

Have your local garage put in some fluorescent dye. Then come back after the number of miles they specify and they will be able to tell where the oil is leaking from with a black light.