Changed the diffy's today Picked a **** cold day to do it -15C. It had to be done and I had Monday off as well.

I am using 75W90 Lucas full synthetic diffy Fluid formulated for use in Limited slip or other diffy types. Plus this is what used to change at 10K

Rear: Fluid coming out was wheat color and very minimal Metal dust on magnetic bolt.

Front: Fluid coming out was Wheat colr as well BUT I noticed a bit of foam on top of the fluid. In fact the pan I used to drain into had a thin layer of foam on it. As I removed the cover I noticed that there was foam/air bubbles stuck to some of the gears.

I am pretty sure it is not water (wrong color ( should be milky gray) and the foam is on top of the fluid, as well as being left behind on the gears suggests that it is lighter than water. It of course came out of the diffy last.

I checked the cover for dry spots or discoloured spots at the gasket line and there was none. So that eliminates some chemical etc infiltrating . So I suppose this is something that is caused inside the sealed diffy.

The fluid is the same (lucas)as what I put back in and has about 40k miles on it.
Any suggestions? any Ideas.

Should I put a bunch of miles on it and pull a sample to send to blackstone?

I have around 10K miles left on my 60k Warranty.

 

I took my truck into the dealer a few months ago...... They phoned to tell me that my diffy fluid was black (whatever) I wonder if they topped up my front diffy with DIFFEReNT fluid. Maybe 2 different fluids would cause foaming.

I went to lucas's website and it specifiacally states not to cause foaming.

 

Was the oil up to temp from driving the truck or was it cold and you just moved it a little into the garage? The wheat color could be due to air that is suspended or from just being cold. Did you let it stand a while to see it the color changed? If you still have some new oil put it in a clear container and place it outside so that it can get to minus whatever it is and see if you get a color shift.

Dealers do very little for free and they would not have changed or added fluid with out putting it on the repair ticket.

 

Water, air, and oil when mixed will make froth that floats. Color is unpredicatble at best. Based on your description it seems a small amount of moisture entered. Check vent tube for location.

 

I changed my diff's at 15k, and the fluid was BLACK. It looked horrible.

 

Servicing differentials in winter time, I've noticed they all seem to be foamy if you check them after a short drive in the cold, before they get up to temperature. Never really noticed this in the summer.

 

I drove to work and around town for a few hrs then I let the truck sit for a couple hours then I pulled it into the garage.

Where can I find the vent tube location? The weather here has been in the low minuses at night and then thawing during the day +5C max. With lots of melting snow...... My front diffy was covered in spray before I took the cover off.

 

Just to give more information, this lucas oil looks and has the consistancey of golden honey. seriousely. I think that because it was -15C that is why it seemed sticky. as far as the "wheat" color I am quite sure it should be that color due to the mileage on the oil itself. it's the foam that concerns me a little.
My theory is this. when the oil inside the diffy gets warm, BUT the casing and surounding metal is cold due to outside temps it may be causing a bit of a thermal shock. For example an exterior window ,on the inside of the house the window pane is 70 degrees on the outside it is 0F. The cold and hot have to meet somewhere so they meet at the glass of the window producing moisture on the glass Sorry for the long posts, just trying to figure this out by giving as much info as possible. It supports the theory by torqufan

 

The gears in the differential whip the oil like a egg beater and cause foaming. Cold oil is thicker and doesn't let the air float out as easily. Synthectics are more prone to foaming when the anti foaming additives are used up. I like to drive arround until the oil is warm before draining. It makes it much quicker. I can't imagine trying to pump or pour gear oil at -15*C.
Billy

 

I know better for next time