jaredytes

I just purchased a 2013 F150 4x4 with around 180k miles. It started doing this right away. Tracing the path leads up to the rail under the bed, which is where the rear diff vent hose is attached. It looked pretty certain that the oil was coming out of that vent line.


But as you can see, the oil that is venting doesn't look very good. It looks to me like it has water in it. If that was the case, and the water got hot enough to start boiling, then that would explain the venting. To investigate, I removed the rear cover. Here is what the stuff coming out looked like:



One never knows for sure, but I don't think that the cover had been removed any time recently. However, there were not any tags to indicate gear ratio, so maybe it was removed at some point. This was a fleet truck, so I would think it had its maintenance on schedule. The fill plug had been removed post-factory, because someone had coated the threads with red RTV. It seems like there are some shops that change out the oil by sucking the old stuff out of the fill port. But if they do that, what is to keep them from not getting it all, then overfilling? After pulling the cover, I let it drain for a while, and it was still dripping 30 minutes later. Perhaps the cover tells a tale, with it's various fluid level lines and rust-colored stains:


I reassembled everything with the special gear oil RTV and filled it with the right stuff. 30 miles later it does not appear to be burping anymore.

Being that I haven't ever worked on differentials before, does anyone have any input about what I'm seeing here? Does my water theory sound plausible, and if so, how does water get in? I don't see any other signs of the vehicle having been submerged. The bed was holding a little rain water when I first got to the truck, but I don't see any way for that to make it in. I suppose there is a chance that someone just put the wrong stuff into the fill port. For now I'm going to consider it fixed and carry on, but I'm still wondering if what got it to that stage is something environmental that could get it there again.

diegoo.jayjay

That truck crossed some type of water. Be a river, flooded area, but something. You're supposed to dump the oil and refill it anytime you cross water that can reach the diff, so yes it is possible again.

gDMJoe

Someone's Captain Nemo and has been testing the depth of the waters.
.

Lee308

Or sitting in a flooded dealer parking lot, there is a vent and the axle seals will let water in while sitting under water.
I would consider not driving out of town for a while.

It should get noisy before leaving you stranded.

M0RRIS

It does sound like you bought a truck that has flood damage.

Spiky

So, nobody's mentioned the front diff, yet? I hope you are checking that, too, OP. If one was contaminated, 2 can be. And the transfer case, that at least has a drain plug.

That is exactly what water-contaminated oil looks like, btw. And it doesn't necessarily mean engine/cab flood damage. But possible.

jaredytes

An interesting follow-up that may provide an explanation... I walked up to the truck a few days ago and the vent line for the rear differential was hanging down with the end on the ground. The plastic end clip that holds it into the channel under the bed has one of its ears broken off. So the line usually stays in place, but apparently under the right circumstances it can come loose. It seems to me that this is a possible way for water to get into the axle, though doubtful it would be that much. I've driven the truck about 1500 miles so far without any other indications of problems.

jeffinthebag

If it was a fleet truck do you know what the company was? Highly doubt it was a flood truck. Not knowing anything, I would assume that it crossed high water somewhere like on a dirt road. Once you refilled it properly, it's good as new. Just do the front too. Any time more than half your tires or up to the axle get submerged. Your supposed to drain and replace the fluid. If you know like on a boat ramp or off roading you will go through high water. Just reroute the vent tube higher so water can't enter it. Problem solved.

jaredytes

I'll do the front, it could probably use it anyway. The truck was last owned by the Dewalt tool people, hence the yellow factory paint.