Want to make sure Im buying correct gear oil for differentials

[Jason in DLH]

I am not going to deny that GM takes overall fuel efficiency into account when they design the drive train and make fluid viscosity selections. That being said, I have heard of very few people that have had an issue with running the recommended fluids if they use quality products and change the fluids out on a proper schedule. I’m willing to bet that most failures are due to folks not paying attention and letting the fluids go way past the recommended service interval. I would never recommend that folks deviate from recommended viscosity, but would recommend using quality product and doing proper maintenance at recommended intervals. There are a number folks on here that have 200K or 300K on their vehicles that use the “legally required” recommended fluids in their vehicles.

I hear you. I have 140K and everything is looking good so far with the recommended viscosity (minus a recently cracked axle housing).

 

[Jason in DLH]

Well said @wjburken . It’s also true that friction generates heat, and I don’t believe running a gearbox at a higher temperature, with more drag will extend the life of the internals.

If anyone is really curious, just measure your differential temperature after driving a test course, then swap out the recommended fluid for some aftermarket super juice and repeat. Have I done that? Yes.

Interesting...how much difference was the operating temp between the two?

 

[HD_LS]

I run Amsoil Synthetic Severe Gear 75W-140. You want to keep the lower number at 75, for great fluidity in cold temps. They've had a number of tests done showing their 75W-140s superior flow at cold temps, and yet they have high film strength at higher temps. Not to mention the lowest wear in various tests.

Lowest running temperature = best fuel economy. Because lowest heat generated = lowest power loss. This is exactly what GM tests for to get best fuel economy. So if you find an oil that generates the lowest temperatures, you have found the best fuel economy oil.

To find the oil that results in the longest life and lowest wear is a completely different set of tests.

 

[Shtiv]

Well said @wjburken . It’s also true that friction generates heat, and I don’t believe running a gearbox at a higher temperature, with more drag will extend the life of the internals.

If anyone is really curious, just measure your differential temperature after driving a test course, then swap out the recommended fluid for some aftermarket super juice and repeat. Have I done that? Yes.

Thank you for the discussion and replies. Are we saying that this Mobile 1 will work fine??

 

[wjburken]

Thank you for the discussion and replies. Are we saying that this Mobile 1 will work fine??

Yes - You should be good to go with Mobil 1.

 

[Shtiv]

Also, I cannot find 80W-90 "SYNTHETIC" gear oil for front diff anywhere.......???? 75W-90 no problem to find

 

[Jason in DLH]

Amsoil carries it...

https://www.amsoil.com/p/severe-gear-80w-90-agl/?code=AGLPK-EA#pills-home_0

 

[Jason in DLH]

Speaking of Amsoil...why in the world is it so expensive?! Are they simply upping their prices to make people think it’s superior than other companies? Or is it just really that good?

 

[Shtiv]

I run Amsoil Synthetic Severe Gear 75W-140. You want to keep the lower number at 75, for great fluidity in cold temps. They've had a number of tests done showing their 75W-140s superior flow at cold temps, and yet they have high film strength at higher temps. Not to mention the lowest wear in various tests.

Lowest running temperature = best fuel economy. Because lowest heat generated = lowest power loss. This is exactly what GM tests for to get best fuel economy. So if you find an oil that generates the lowest temperatures, you have found the best fuel economy oil.

To find the oil that results in the longest life and lowest wear is a completely different set of tests.

I assume this can be used front and back????

 

[Jason in DLH]

I assume this can be used front and back????

You have to make sure you have limited slip additive for the back if your truck is equipped.