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Chris Tokarski
New User
Username: 49bentley

Post Number: 13
Registered: 10-2024
Posted on Sunday, 10 August, 2025 - 23:52:   Edit PostDelete PostView Post/Check IP

Good Day. I need to refill my differential oil. Which type is best? There are so many out there. Synthetic or mineral?
Thanks for your help
Chris
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 3444
Registered: 06-2009
Posted on Monday, 11 August, 2025 - 06:37:   Edit PostDelete PostView Post/Check IP

Truly, any modern EP (extreme pressure) gear oil that meets API GL-4 or GL-5 that "maxes out" at 90W or above should be fine.

There's an awful lot of EP 80W-90 and 85W-90 out there to choose from that meets API GL-5.

I'm completely agnostic on mineral versus synthetic versus blend.

Brian
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 737
Registered: 07-2018
Posted on Monday, 11 August, 2025 - 08:19:   Edit PostDelete PostView Post/Check IP

Synthetic is good if you park your car in very cold or below zero temperatures, it is the correct viscosity.
Dinosaur oil is thick at those temps and isn't good for any gears until it warms up.

If your rear end is leaking badly avoid the synthetic because it will drip excessively when parked.
If it is leaking that much however, it will lose a fair amount with regular oil when driving, so it will need attention sooner then later.

Synthetic is said to be more slippery and stick better to the gears and in cases that concerns standard transmissions with worn synchro cones, it is better for that.

I use Red-Line synthetic in my trans, but I still have the regular oil in my diff, and it's fine.
Pennzoil 80/90 weight gear oil.

I've never touched the rear in my car, and if I do, I will move to synthetic.
I should one day, there is more play in it then there should be.
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Chris Tokarski
New User
Username: 49bentley

Post Number: 14
Registered: 10-2024
Posted on Tuesday, 12 August, 2025 - 00:54:   Edit PostDelete PostView Post/Check IP

Thanks Brian and Jeff.
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ChristopherCarnley
Unregistered guest
Posted From: 86.175.234.172
Posted on Monday, 11 August, 2025 - 19:11:   Edit PostDelete PostView Post/Check IP

The original specification was Castrol Hi-Pres SC.

This is the same as Castrol EP140, I use it in all differentials.

(Message approved by david_gore)

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