Oil on rear of gas tank?

[HangmanNY]

While doing Transmission Service, transfer case, and front differential fluids, I noticed that there’s oil on the back edge of the gas tank. Right in front of the rear differential.


About a year and a half ago I was driving at night and some idiot dropped a 5 gallon bucket of joint compound on a main road . I didn’t have time to swerve because of oncoming traffic.

I was cleaning that crap off from the underside of my truck for quite a while. This happened up north.


There was an oily film on the rear bottom of the gas tank has me concerned. I ordered a PPE rear differential cover. Because it has a drain plug and a fill plug. It has not arrived yet. And I have a lube locker gasket for it.

I cleaned away the oil residue on the rear of the gasoline tank.

Is it possible that the drive shaft seal could leak where it connects to the rear differential? Or could it be something else that I’m missing? I was wondering if that 5 gallon bucket of joint compound hit something. To the best of my knowledge. I have no leaks in the system. I did the rear differential fluid about 2 1/2 years ago. But that’s with the factory differential pan with a rubber plug. I’ll check the fluid level tomorrow.

Thanks for any helpful advice!

 

[HangmanNY]

I checked my rear differential fluid. I pulled out the existing rubber cap. The truck is level. And the rear differential is full.

I can’t figure out where that oil on the bottom rear of the gas tank came from?

 

[stenerson]

Are you losing any significant amount of engine oil? Did you wash it off and check again after a while? (I'm sure you probably did but doesn't hurt to ask).

 

[HangmanNY]

I did the engine oil about 4000 miles ago. I’m using the HPL oil. Rated for 10,000 miles but I generally do it around 7000 or 8000 miles. I bought about 10 of the mobile one oil filters about five years ago.

Just checked it again and the level is about an eighth of an inch down from the maximum fill mark on the dipstick. The truck has 160,000 miles on it. I know it burns a slight bit of oil over the lifespan of the oil change.

I don’t remember seeing any oil around the drain pan. However, one of my pet peeves is where they put the oil filter. It drips down over the exhaust pipe and a few other things. I’m usually very diligent about getting up in there with blue shop cloths and wiping it up. So it doesn’t wind up dripping on the driveway. There is a remote chance there could’ve been a few drops of oil in that area.

The truck’s been sitting for a couple of days level in the driveway. I’m waiting for the new PPE real differential cover.