Rear Diff, thick or thin

[nicholas]

Hey Guys
I am gonna change the rear diff fluid in my little RAV-4.
It specs 80w-90 fluid. This is hard to find where I am .
I was going to buy either 75w-90 or 75w-140 synthetic fluid.

I have never had a 4wd vehicle before, so I thought I would a more knowledgable crew.
thanks
have a good weekend

 

[Pablo]

In your climate, vehicle size and output, stick with 75W-90. In general thicker in diffs (at temp) has some protection beni's - but I highly doubt it's worth it for the MPG loss in your case.

 

[LargeCarManX2]

Order the Amsoil AGL 80-90 from Don....the Canadian Sponser. I use it in many different rear ends and it is the most reasonable in cost factor.

 

[unDummy]

Any of the 75w90 synthetic gear oils will work well!

 

[wantin150]

Noob question here but wouldn't it be better to use a 75w90 in Canada vs an 80w-90 anyway due to the colder temps there?

 

[Pablo]

Yes wantin'. You'll be wantin' 75W-90 in Canada.

 

[Slick 55]

Amsoil Severe Gear 75W-90 is what you want.

 

[Idrinkmotoroil]

I had the same decision to make with my Ford Escape, I decided to go with Redline's 75w-90. Everyone I spoke with said 75w-90 is fine for use where 80w-90 spec'd diffs, I chose Redline because I like the viscosity specs of their fluid , both cold and hot.

I think Amsoil has a 80w-90 if you want to stick with it, otherwise Amsoil and Redline both have good 75w-90's.

I think 75w-140 is too thick for your diff. I run Amsoil's 75w-140 in my transfer unit but Ford spec's that viscosity in the transfer unit so I stuck with it there.

 

[Whimsey]

Are you sure that Ford spec's 75W-140 gear oil for your transfer case? I have a 2002 F-150 4X4 and my transfer case uses Mercon ATF. My rear diff uses 75W-140 gear oil and my front diff uses 75W-90 gear oil. Though I did use Schaeffer's 80W-90 synthetic blend gear oil in the front diff and have not had any problems with the previous winters here in NJ.

Whimsey

 

[Idrinkmotoroil]

Quote:

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Are you sure that Ford spec's 75W-140 gear oil for your transfer case? I have a 2002 F-150 4X4 and my transfer case uses Mercon ATF. My rear diff uses 75W-140 gear oil and my front diff uses 75W-90 gear oil. Though I did use Schaeffer's 80W-90 synthetic blend gear oil in the front diff and have not had any problems with the previous winters here in NJ.

Whimsey

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yes our transfer case on the escape 4x4 uses 75w-140 , it comes from the factory as a synthetic fluid. I would have thought other Ford trucks may be the same but I guess they all use different parts depending on application. Our owner's manual says that we can use 75w-140 in the differential if the vehicle is used for long durations in very cold temps (colder than -20 degrees) for improved winter operations (more likely due to it's synthetic composition rather than it's viscosity). The differential calls for 80w-90, and Mercon ATF in the auto transmission.

 

[Reg# 43897]

Strange - one would think that they would allow for a ninety-weight in cold weather rather than a 140. It would also allow for a bit better efficiency.

John.

 

[LargeCarManX2]

Quote:

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Noob question here but wouldn't it be better to use a 75w90 in Canada vs an 80w-90 anyway due to the colder temps there?

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75 or 80 starting weight has got to be so close it really won't matter. And 75 or 80 starting grade avaliability should be a consideration. The Amsoil 80-90 is quite a bit cheaper per OCI than the Amsoil severe gear oils. The main factor in cold weather is that synthetics flow at a colder temp and protect your drivetrain better.

I look at it like the group III vs. group IV V debate...there so close...and, both work wonderfully.

I did see where the severe gear OCI is very short compaired to the standard OCI of synthetic gear fluids....why? additives deplete faster in it?

 

[bmwtechguy]

Please elaborate on the "very short OCI of the severe gear" fluids. The long OCI's of some of their diff fluids refers to their recommended use in the big OTR trucks only, but when used in passenger cars and trucks I think may have the same intervals as the Severe Gear. This is what I gleaned from some of Amsoil's literature.