Thicker isn’t always better, but is it for rear differentials? Jumping from 75W85 to 75W110 in a Torsen LSD

[VQAndrew]

I have a 2022 Mustang GT and the performance pack comes with a Torsen rear LSD. I am gonna be draining out the factory fluid at about 12K miles and swap to Amsoil SevereGear which is raved about. OEM fill is a 75W85 but many think that’s mainly for fuel efficiency and is “good enough”. I know for engine oils and transmission oil thicker isn’t necessarily always better and you should stay somewhat near OEM spec unless highway modified as modern engines and transmissions have extremely complex oil passageways. Do Torsen diffs have any downside to run a thicker oil such as 75W110 besides a small decrease in fuel economy? They seem to be just pumpkins that oil sits in, or do they require thin oil for certain lubrication channels like powertrains?

I was thinking of jumping to 75W110 as it should be more protective at high temps in the summer when driven hard but the car is also driven in the freezing winter and don’t want something too thick to affect anything in the cold temps. Is 110 vs 85 a gigantic jump in viscosity?

Any input helps thank you

 

[ripcord]

Ford spec'ed 75w-140 in a lot of heavy vehicles in the past to reduce wear that they were seeing with 80w-90. That said, your choice of 75w-110 would be a fine one. It will provide good protection and only hurt your mileage by an imperceptible amount.

 

[Pablo]

I have a 2022 Mustang GT and the performance pack comes with a Torsen rear LSD. I am gonna be draining out the factory fluid at about 12K miles and swap to Amsoil SevereGear which is raved about. OEM fill is a 75W85 but many think that’s mainly for fuel efficiency and is “good enough”. I know for engine oils and transmission oil thicker isn’t necessarily always better and you should stay somewhat near OEM spec unless highway modified as modern engines and transmissions have extremely complex oil passageways. Do Torsen diffs have any downside to run a thicker oil such as 75W110 besides a small decrease in fuel economy? They seem to be just pumpkins that oil sits in, or do they require thin oil for certain lubrication channels like powertrains?

I was thinking of jumping to 75W110 as it should be more protective at high temps in the summer when driven hard but the car is also driven in the freezing winter and don’t want something too thick to affect anything in the cold temps. Is 110 vs 85 a gigantic jump in viscosity?

Any input helps thank you

Not really a large jump when you consider 110 is just the upper half of the OLD 90 viscosity range

 

[DemoFly]

SAE split the range of old 90w because the acceptable range was too broad. The thicker range became 75w110, essentially just a thick 90 of yore.

140 is an even greyer area because 140 has historically been anything thicker than 90. The viscosities vary wildly brand to brand.

Anything GL-5 90 or above will be fine for your application. For a streetcar I'd personally put 75w90 in it. If its a summer track car I'd put 75w140 in it.

 

[Falcon_LS]

I'm running nothing but 75W-140 in my Torsen T-2. Used to be Motorcraft, later switched to Amsoil. Then again, this is what the factory recommendation was for the open diff my car originally came with and I stuck with it.

 

[zray1]

I use Mobil 1 75w-140 in my ‘02 Jaguar rear end, as it has a reputation for excessive and premature wearing.

With 185,000 miles on the car and more on daily basis, I need to do whatever I can to slow down the wear.

I’ve used the same lube in numerous vintage cars, both USA and European. It seems to help.

 

[ka9mnx]

I moved to 75w-140 when the SAE lowered the 75w-90 ratings about 20 years ago. 75w-110 was a boutique oil and too rich for me. It was a fuel economy move by the SAE. Remember, whether a 75w-90, 75-110 or 75w140, it's still a 75w at cold temps. No MPG hits on my vehicles but I live in a warmer climate.

 

[Cujet]

I use Mobil 1 75w-140 in my ‘02 Jaguar rear end, as it has a reputation for excessive and premature wearing.

With 185,000 miles on the car and more on daily basis, I need to do whatever I can to slow down the wear.

I’ve used the same lube in numerous vintage cars, both USA and European. It seems to help.

What Jag? My F-Type V6s does have a early reputation for differential failures. I do notice some noise and vibration seemingly coming from the differential at high speeds.

 

[tcp71]

My truck came with 75w90 in the rear differential. I changed it around 12k miles with motorcraft 75w140 that has been spec'd forever before the 2015 models came out with the 75w90 fluid. It's fine down to -35C and fine for towing at 38C in my experience.

 

[zray1]

What Jag? My F-Type V6s does have a early reputation for differential failures. I do notice some noise and vibration seemingly coming from the differential at high speeds.

It’s a 2002 XKR (4.0 liter supercharged). It’s the stock open rear. I don’t know if the F type shares any of the components with the XKR’s, but it wouldn’t surprise me if that were the case. If you are not already using the M-1 75w-140, then try it. It might put off an expensive repair indefinitely.

Z

 

[SubieRubyRoo]

What does Torsen recommend? Not the Ford recommendation, but the diff mfr directly like if you were to retrofit it?

There’s little harm in going to a 75w110, but the testing reported in my thread on 75w90 gear oils shows Amsoil, HPL, and Motul are no slouches in the protection department. I just drained my factory fill diff at 76k and the oil was perfectly clean, looked essentially new.

 

[JohnnyG]

Does this help?

 

[Pablo]

Does this help?
View attachment 188847

No that's pretty old.

 

[JohnnyG]

Got a newer one?

 

[Pablo]

Got a newer one?

Will post one later after I get back to my pc
From Widman!

 

[Overfill]

I was under the impression that gear wear is treated as boundary lubrication. So, unless changing the viscosity is helping the oil transport to the wear surfaces through sling, cling, or pumping, viscosity changes shouldn't do much to decrease wear.

 

[zray1]

I was under the impression that gear wear is treated as boundary lubrication. So, unless changing the viscosity is helping the oil transport to the wear surfaces through sling, cling, or pumping, viscosity changes shouldn't do much to decrease wear.

I’m going with “cling”.

Z

PS: besides, the 75w-140 costs more. So it has to be better, right?