Transfer case factory spec is 80w90, can I go to 75w90?

[AVR2]

I have a 2002 Ford Escape for which the factory spec fluid is 80w90 GL5 in both the rear diff and transfer case. I know I can go to fully-synth 75w90 for the diff, but can I also use it in the TC? Logic suggests yes, if the factory spec oil for the TC is the same as for the diff then it should be no problem. And of course, I have no guarantee that it's always been filled with the factory-spec fluid up till now anyway.

 

[JLTD]

My opinion is yes.

 

[CharBaby]

Yes, I've done this on many vehicles.

 

[sdowney717]

The second number is more important, the first number is when its cold oil. Definitely use either of those.

 

[Gebo]

You can get Amsoil 80W90 fully synthetic if you like. IDK if there is another fully synthetic gear oil. On the other hand, I don't think there will be any problem going to the 75w90. "Everybody" does it.

 

[sloinker]

Red Line sells synthetic gear lubes. In your case I would buy the cheapest off the shelf available from walmart for your application.

 

[Oro_O]

Originally Posted by sdowney717

The second number is more important, the first number is when its cold oil weather. Definitely use either of those.

Agree the second number (at temperature) is the more important. BUT, the first number like in motor oil refers to how it flows in very cold weather ("w" = winter), not when the oil is cold. An 80w-90 is a smarter choice, apples to apples, unless you live in a climate with very cold winters. For the OP, an 80w-90 is a better choice in the UAE unless it's hard to find, vastly more expensive, or only available in dino and the 75w-90 is full synthetic. In that last case, it might even be a better idea to use the alternative.

 

[AVR2]

Thanks guys. I can't find synth 80w90 anywhere here, only semi-synth or mineral (I'm in the UK, although the location in my profile previously said the UAE, where I lived for 10 years) but full-synth 75w90 is easy and cheap to get.

 

[AVR2]

OK, I'm in another quandary! It's got the manual transmission and the recommended fluid for that is 75w140. I can get a great deal on 5L of fully-synth 75w140 (the gearbox/front diff assembly alone takes 2.2L), so is there any reason not to use 75w140 in the rear diff and TC as well, since 5L would cover me for a complete driveline fluid change?

 

[JLTD]

Originally Posted by Oro_O

Originally Posted by sdowney717

The second number is more important, the first number is when its cold oil weather. Definitely use either of those.

Agree the second number (at temperature) is the more important. BUT, the first number like in motor oil refers to how it flows in very cold weather ("w" = winter), not when the oil is cold. An 80w-90 is a smarter choice, apples to apples, unless you live in a climate with very cold winters. For the OP, an 80w-90 is a better choice in the UAE unless it's hard to find, vastly more expensive, or only available in dino and the 75w-90 is full synthetic. In that last case, it might even be a better idea to use the alternative.

Uh, the oil flows based on oil temperature not outside temperature. For example, oil can be 100C when it is 0C outside.

Originally Posted by AVR2

OK, I'm in another quandary! It's got the manual transmission and the recommended fluid for that is 75w140. I can get a great deal on 5L of fully-synth 75w140 (the gearbox/front diff assembly alone takes 2.2L), so is there any reason not to use 75w140 in the rear diff and TC as well, since 5L would cover me for a complete driveline fluid change?

Rear diff is probably ok. TC is a "?" since it might cause shifting issues; you can always experiment.