I'm a bit confused here guys... Differntial Fluid (gear oil) viscosity

Myco

Myco

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I've read that the manual for our cars (97 Mark viii) calls for 75/140 viscosity gear oil, but have also read from forums that 75/90 is the viscosity to use.

I was about to go pick up some gear oil (mobile 1 Full synthetic).

Which is the viscosity to use? ( I live in Houston where it gets HOT btw )

Thanks
 
Yep. There's something else I need to do to my car:) I doubt the gear oil has ever been changed. I'm kind of afraid to change it now that the car has 205k miles. The old gear oil may be the only thing holding the rear end together:lol:
 
I just looked this up on AllData today at work. The viscosity listed there for a 98 is 80W90.
 
I use Redline 75W90

From the Factory Service Manual:

SAE 80W-90 Premium Rear Axle Lubricant XY-80W90-QL

And the Owner's Guide:

Motorcraft Premium Rear Axle Lubricant XY-80W90-QL WSL-M2C197
 
Last edited:
DLF said:
I use Redline 75W90

From the Factory Service Manual:

SAE 80W-90 Premium Rear Axle Lubricant XY-80W90-QL

And the Owner's Guide:

Rear axle Motorcraft Premium
Rear Axle Lubricant
XY-80W90-QL WSL-M2C197
Click to expand...

Thanks DLF. You have verified that the fluid used in my recent diff. work was correct. I was actually concerned that he used that because I thought it should be heavier. If you use it, I trust your judgment over anyone else's. ;)
 
When I did mine I rebuilt the Trac loc with the carbon fiber clutch pack. I believe it called for the 140 + the additive of course.
 
valvoline 80-90 durablend here. semi synthetic. no friction modifier. cobra carbon clutches. and the rear is very stiff. i can hear the inside tire spin a little on tight low speed turns.
 
Digging this up because I used the search. ;)

I also live where its hot. South Louisiana. I'm having the trac loc put in with 4.10's and new bearings. Seems as if I should use 75-90 or 80-90. I'm not savvy with the weight and weather differences. Should I go with 80-90? And what brand as well is recommended?
 
I usualy Run just plain old 80w90 gear oil. If there is a limiter slip or trac-lok rear end I add a friction modifier.
 
Dropping everything off today. Spare rear chunk (polished, couldn't help m'self!) 4.10 gears, new bearings, trac loc. and will be picking up some Mobil 1 80w90.


Question is, how much does it take?
 
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