Rear Axle Venting Oil

[V8BoatBuilder]

While under my truck today greasing the slip yoke, I noticed that a decent amount of differential fluid had worked its way up the vent tube and splattered over the spare tire and shock. I topped off the diff with fluid, it took maybe 1/8 of a quart.

What could have caused the diff to vent? Is it a probem? Besides cleaning up the mess, anything I should do?

Thanks.

 

[dogfriend]

Hauling heavy loads?

Drive 90mph on the freeway for hours at a time?

Wheeling with the truck at extreme angles?

The purpose of the vent tube is to allow the fluid to expand when it gets warm (hot). So either you got the fluid hot or the truck was at an angle that allowed some fluid to escape thru the vent.

 

[V8BoatBuilder]

Been logging a lot of freeway miles at around 70-75mph... Done a fair amount of towing as well. Not part of the rollover posse (knock on wood)

I'll just keep an eye on the level. Would extending the line help out?

 

[dogfriend]

I know that some on the board have extended the vent tubes, but usually to avoid taking on water on stream crossings. It could help in your situation.

You might want to consider changing the diff fluid if its old because it can get thinner in viscosity (molecules get sheared) as it ages. This can happen with both dino and syn fluid although syn fluid should resist it better. I'm pretty sure that Ford used syn gear oil in yours because of the V8

 

[Opera House]

I just changed the rear diff oil on my 97

Basically had to because the wheel seal was leaking. It was nasty, almost black, and the magnet was covered. Wear looked fine but I replaced with higher wt oil. Interesting that the front oil still looks pristine. Heard the venting is usually a sign of water getting in. You wouldn't be dunking this in the water would you? My vent hose was also cracked off when I bought it. Different things make me think mine was a flood vehicle once.

 

[V8BoatBuilder]

I changed the diff oil with Valvoline DuraBelnd Synthetic 75w-140 and Ford OEM friction modifier about two months ago. (It's the 3.73 w/TracLoc)

I have been going through some water up to 6" deep recently. (All this NE rain...)

I'm definitley going to extend the lines, think its worth opening the diff, again?

 

[Alec]

You should definately check the fluid condition. If it's at all milky or otherwise seems to have water in it, you need to change it.

You shouldn't have to open the diff up to check the fluid, you should be able to do it through the fill plug.

If you do have to change the fluid, this would be a good time to get a new diff cover with integrated drain and fill plugs