Front diff pushing fluid out vent tube

My front differential on my 97 Silverado Z71 sometimes vents some fluid out of the vent tube. I end up smelling it in the interior while driving. The vent tube top is above the top of the radiator and has the little cap on it. The first time it did it, was during a heavy rain. I had it in 4wd on the freeway doing around 60-70 mph. I figured it was because I was in 4wd. It did it yesterday after a 35 mile drive on the freeway again, but I was in 2wd the whole time. Outside air temp was over 100 degrees and I am using Royal Purple fluid. I checked the level a couple of weeks ago and it was below the fill plug about 1/2 inch.

Any one know what would cause this? I've also done the electric motor actuator conversion on the front axle.

Thanks

It's a vent tube. There is a hole at the top for it to vent. Duh.

It's a vent tube. There is a hole at the top for it to vent. Duh.

right ! the vent tubing has a opening for the fluid or really air to vent out and in as the box heats/cools. this is so the seals do not get damaged. the rear diff is with the same venting.

what I think is the box is getting too hot.

are the front tires the same size/wear. if one tire has more tread than the other this damages/heats the box. left/right wheels must rotate at the same RPM.

I use 80-90wt OEM gear oil. I have had no problems with this oil. after the breakin 10,ooomi the gear oil looks good . I replace it at 40,ooomi after this first 10,ooomi. . 138,ooo mi now on the 2000 4X4 ..just did the tranfercase fluid today.

had issues when the vehicle had less than 10,ooomi . oil had to be changed 3X.

Tires are identical with even wear. 126k miles. What kind of problem caused you to change the fluid 3 times.

Tires are identical with even wear. 126k miles. What kind of problem caused you to change the fluid 3 times.

gear box oil was turning a gray color. after the oil changes and 10,ooomi on the vehivle , this has no longer been an issue .

remember if you operate in auto 4WD the front diff is locked . this would also create heat on solid dry pavement.

with the fluid your using its possible that it expands more with heat.

when cold the fluid should be 1/2 inch below the fill hole.

I had this happen in my truck once and for the life of me i don't know what set it off, it never happened again. Maybe one tire in the front was way lower than the other side.