Differential fluid change. When should I do it?

[wtd]

This is on my 98 chevy ext-cab Z71 with the locking differential. The owners manual says to change every 15,000 miles if you drive in dusty environments or tow a trailer. I tow a 5X10 utility trailer loaded with plumbing pipe and supplies a few times a month.

I use 75W-90 Mobil 1 diff fluid in front and rear and was wondering if this fluid will allow me to safely go beyond 15,000 mile changes? I currently have about 23,000 miles on the rear diff fluid.

I had a small leak at the rear cover that would drip occasionally. The fluid still looked as clear as when I put it in.

What do you think, should I change it out or can I go longer?

Wayne

 

[UncleS2]

Unless that trailer's awful heavy, & assuming you don't do a lot of off roading, I'd think you could surely run it 20-25 K miles. Or are those particular rear ends extra hard on the lube?

I would fix that leak, though.

 

[sprintman]

Analyze it. Good to know how its holding up IMHO.

 

[Dominic]

You won't go wrong changing it every 15,000 miles. However on a previous chevrolet truck we used to tow a boat with the differential fluid looked brand new at 15,000.

You can probably safely go 30,000 without worry if its good fluid. On my Camaro I change the differential fluid every 30,000, along with the manual transmission fluid (ATF for me) - they go hand in hand wear wise it seems.

 

[Dick in Falls Church]

Wayne-
Unless you park it under water, you can probably go 100,000 miles or more without having to replace it. Over-the-road trucks have tested their AMSOIL synthetic gear lube (also PAO base) at 500,000 miles and found it still good.

 

[MolaKule]

My experience from recent analysis in three separate differentials suggests that you change according to man. recommendations regardless of the type of oil used.

I would also highly recommend you have a used GL lube analysis done every 15,000 miles.

Gear oils do have a tendancy to thin at first and then oxidize to a thicker grade over the longer run.

Redline GL's might be the exception. I haven't used Redline yet but intend to Run it's gear oil and compare it to what I'm running now.

 

[MolaKule]

In my view, Chevrolet differentials are not the most robust.

In OTR truck differentials, you have much larger drive pinions and rings gears so while the forces due to DI engine torque are greater, the tooth forces are spread out which relates to lower contact pressures. In addition, there is much more lube present in the case; the lube is stressed less and the larger surface area permits better cooling of the lube.

In light truck differentials, you have smaller fluid capacities and higher tooth pressures,
hence the need for more frequent changes. If the OEM LT manufactures would just integrate cooling fins into the differential case casting, it would sure lower fluid temperatures.

 

[wtd]

Guys,
Thanks for the replies. I guess I'll probably change it out soon. I don't want to take any chances of ruining the rear end. I'll probably get an analysis done to see how well its holding up.

Wayne