front Diff vent tube

Hi, new here and am quite impressed with the knowledge on here. After scrolling through the messages I found one that asks the same question that I have. Hopefully someone can help. When I am driving my 94 Sierra 4x4 in 4H, fluid comes out the front diff. vent tube attached to the fan shroud. It smells like gear oil and makes a pretty good mess in there. What could be causing this problem? I'd really like to get this thing sorted out.
Thanks

I would check the oil level sounds like it may be way over filled the oil will expand when headed up and the vent is only there so the psi. can escape other wise it would blow out the axle seals psi. is like electric the path of least restiance.

Thanks ridered. I'm going to change the fluid this weekend and see what happens.

I just drained & refilled mine diff. should take about 2 1/2-3qts of oil

Have you been driving in deep water? If you get water in the differential it will puke fluid out of the vent hose.

Have you been driving in deep water? If you get water in the differential it will puke fluid out of the vent hose.

Not water but deep snow.
When I changed the fluid last weekend the stuff that was in there was as black and thick as tar. I just bought the truck last month. It has 120,000 KM's so I don't think any of the fluids have been changed.
I also unscrewed the plastic cap that the vent tube connects into on the diff and cleaned and loosened up the fitting ?? that's attached on the inside. Put it all back together and filled the diff with 75W90 synthetic oil. I must have overfilled it as it came out the tube for a bit and now seems to be ok.
Thanks.