Oil coming out of differential vent....normal?
 

Hi all,

I'm stumped! I have a small amount of diff oil that comes out of the differential vent after almost every drive, especially during very hot weather. I have read every single thread on the subject and I don't know where to go from here. Here is what I know:

1) I changed the differential oil last year. I filled it with GM synthetic gear lub and the GM additive. This was done near the end of the summer so it never got hot until this year. Yes, the car was level when I filled it.

2) I first noticed diff oil coming out of the vent hole on the top of the diff about a week ago after a one hour drive during a very hot day. I definitely know that this is not the "leaky butt syndrome". My car has had the recall performed and I checked the driver side diff cover. It does not appear to be leaking nor does it appear to be leaking from the left axle shaft seal. All of the oil appears to be coming from the top next to the vent hole and flowing down to the bottom of the diff casing.

3) I know that the vent is working properly because when I opened up the fill plug after the diff had cooled, there was a woosh sound suggesting that there was a slight vacuum buildup in the diff. This also proves that the vent did open to evacuate excessive pressure (and some oil) and maintains it seal once cooled.

4) As recommended in some of the threads I read, I re-verified the oil level hot (half hour after drive). There was about 1/8th of a cup that came out of the fill hole. At this point I thought the problem was solved.

5) I went for a drive yesterday and again, I have a quarter sized drop of diff oil on my garage floor. I checked the diff and it is still coming out of the top vent. However, it does appear to be much less than before.

So, there you have it. I have done everything possible and where do I go from here. Is this "venting" normal when driving the car during hot wheather? Should I be concerned? Any help would be greatly appreciated.

PS: My car is a MN6 with a 3.42 rear and 31K miles.

Thanks,

Bump. Anyone?

I remember when I got my 3.42 rear installed this year that my installed filled it not up to the hole but like 1/8" below based on a service bulletin. I thought he said that there were reports of it leaking out of the top (may have said vents).

I had a 99 Vert that did the same thing. It happened after I bought the car and had the side cover and seal leak. We took a 2 hour drive and when we came back it burped oil. I was afraid it was the seal leaking again. I thought the diff might be low so I wanted to check before I drove it anywhere. when I pulled the plug to check it I had fluid come out at me. I siphoned off enough so that it was just below the fill plug and it never did it again. I think the vent relationship to the oil fill plug is so close that a slight over fill will cause it to burp. A slight amount below the fill plug is better than an over fill. It makes a real mess all over the rear end and it hard to clean!

I just had a diff with 3.90's swapped in and the fluid was way over-filled and is leaking out the vent hole. I have been too lazy to get back under there to drain-out the excess. I am hoping that enough will leak out to finally stop leaking:)

Thanks guys. I appreciate your input. I guess I will keep my eye on it and hope it will eventually stop.

Just remove the fill plug and let a little drain.You can't drain to much out of the fill plug..That stuff stinks too much to let it just keep do that..

Use a squeeze bottle with a piece of plastic tubing and suck out a small amount like 2-3 oz. Just so it is below the fill plug. That stuff makes one heck of a mess on the rear of a car.

During shop night this past Wednesday night at Win Kelly Chevrolet I had the car on the lift changing oil and I asked the the Corvette mechanic about my rear fluid loss. He looked and said there was no seal leak, the fluid was coming out of the vent. He said the fluid level should be 1/4 inch below the fill hole. Basically you can drain a little fluid or drive until enough is vented :-). Cool beans!

I'll second that (Cool Beans). Glad for you.