Have gear oils gotten thinner?

[2000Trooper]

I know there is no real basis for this, but I typically change my differential oil every ~30k or so. I always use synthetic 75w90. This time around I bought some valvoline synthetic 75w90 gear oil and I couldn’t help but to notice how it flowed so well and easily, almost like water. I’m used to gear oil being viscous and flowing slowly so it was an interesting experience. Has there been a push for thinner gear oils within their grade similar to motor oil for mpg or maybe a push for better quality gear oils? Or is this all just in my head?

 

[blufeb95]

It's actually thicker at 100C than there 80W90 conventional oil, the 80W90 has a lot of Solvent refined residual oil in it with a viscosity index similar to that of monograde motor oil, it's pretty similar in viscosity to straight 40 grade oil, whereas the synthetic is made with severely processed crude oil and Viscosity Improvers. The valvoline 80W90 is kinda thin for grade with a KV100 of 14.7CSt while the 75W90 is 15.6 which puts it closer to the middle for SAE 90 13.5-18.4CSt. but the KV40s are astoundingly different, 145 for the 80W90 conventional and 92.5 for the 75W90 synthetic, when you consider that and the poor viscosity index at room temp and colder the 80W90 will seem incredibly thick compared to the synthetic.

 

[Accent Abuser]

I know there is no real basis for this, but I typically change my differential oil every ~30k or so. I always use synthetic 75w90. This time around I bought some valvoline synthetic 75w90 gear oil and I couldn’t help but to notice how it flowed so well and easily, almost like water. I’m used to gear oil being viscous and flowing slowly so it was an interesting experience. Has there been a push for thinner gear oils within their grade similar to motor oil for mpg or maybe a push for better quality gear oils? Or is this all just in my head?

Maybe you did your last change in the winter? I can't speak for gear oil, but with motor oil I can't tell the difference between 5w-30 and 5w-50 just by pouring in the summer.

 

[Jetronic]

Gear oil viscosity classifications changed a few years ago. 90 was a very wide grade, with 100C viscosities ranging from 13.5 to 24 cst. Above 24 cst they became 140 oils.

Now they added the 110 viscosity grade from 18.5 to 24 cst, so the thickest 90 grade oils have gone now.

250 got split in 190 and 250 aswell.

Lot's of old SAE J306 tables are still going around so be careful with those.

 

[ka9mnx]

Gear oil viscosity classifications changed a few years ago. 90 was a very wide grade, with 100C viscosities ranging from 13.5 to 24 cst. Above 24 cst they became 140 oils.

Now they added the 110 viscosity grade from 18.5 to 24 cst, so the thickest 90 grade oils have gone now.

250 got split in 190 and 250 aswell.

Lot's of old SAE J306 tables are still going around so be careful with those.

And why I (and Ford) are now using 75w-140. The change was around 2002.

 

[MolaKule]

And why I (and Ford) are now using 75w-140. The change was around 2002.

Are we discussing differentials or those Ford Power Transfer Units?

 

[ka9mnx]

Are we discussing differentials or those Ford Power Transfer Units?

Differentials. The diff was rebuilt by Ford in my Ranger under warranty shortly after I purchased new. When I looked over the invoice I noticed they replaced the axle oil with 75w-140. I asked the mechanic and he said it was Ford's new policy (TSB) which led me to research why the change.

 

[Snagglefoot]

Here is a listing of gear oil put together by member Sonic67. There is a variance.

 

[BBDartCA]

Differentials. The diff was rebuilt by Ford in my Ranger under warranty shortly after I purchased new. When I looked over the invoice I noticed they replaced the axle oil with 75w-140. I asked the mechanic and he said it was Ford's new policy (TSB) which led me to research why the change.

In addition to the TSB you reference, our 2006 V6 Mustang owner’s manual and FSM both call out 75w-140 synthetic for the differential. And yes, Synthetic specIfically (with some FoMoCo spec references).

 

[WobblyElvis]

I put Amsoil synthetic gear/differential oil in the axle of rear wheel drive Chev Malibu many years ago. I swear it would roll easier in extreme cold weather upon first startup.

 

[Dave9]

Differentials. The diff was rebuilt by Ford in my Ranger under warranty shortly after I purchased new. When I looked over the invoice I noticed they replaced the axle oil with 75w-140. I asked the mechanic and he said it was Ford's new policy (TSB) which led me to research why the change.

Probably factory fill is to help meet fuel economy #'s just as the thinner motor oil does, then once the # is established, switch back to what offers better protection if customer use causes service.

 

[MolaKule]

In addition to the TSB you reference, our 2006 V6 Mustang owner’s manual and FSM both call out 75w-140 synthetic for the differential. And yes, Synthetic specIfically (with some FoMoCo spec references).

Yes Ford later found the loading on their differentials was higher than originally designed so the change to 75W140 was mandated.

The change to 75W140 for some of their PTU's was because of the low sump volume and the high temperatures encountered because of the PTU's placement.

Many Differential oils have been formulated to a 75W85 Grade (e.g, GM's "grape juice") to obtain a miniscule increase in the fleet's MPG rating. The formulation uses new EP chemistry with a slight drop in bulk oil viscosity.

 

[Gebo]

For a simple mind, can we say that the "new" 110 was the "old" higher viscosity 90?

 

[Jetronic]

For a simple mind, can we say that the "new" 110 was the "old" higher viscosity 90?

That's exactly what it was, and the new 190 was the old thin 250

 

[BBDartCA]

Yes Ford later found the loading on their differentials was higher than originally designed so the change to 75W140 was mandated.

The change to 75W140 for some of their PTU's was because of the low sump volume and the high temperatures encountered because of the PTU's placement.

Many Differential oils have been formulated to a 75W85 Grade (e.g, GM's "grape juice") to obtain a miniscule increase in the fleet's MPG rating. The formulation uses new EP chemistry with a slight drop in bulk oil viscosity.

Yes. Lube band-aid for a poor component Ápplication

 

[2000Trooper]

Hmm... so on an unrelated note we have a Chevy 2500HD diesel and the manual called for 75w90 in the differentials which I thought was interesting as it’s rather light. I was under the impression heavy duty trucks used 75w140. But not working on big trucks for a living and knowing 75w90 is typically your standard I went with it anyways. We use this truck to haul horses around. Now I’m wondering if I should have used 75w140 or even maybe 110. It’s a 2015 model so it’s past the classification changes you guys mention so in theory the engineers should have accounted for it when they speced the fluids. I’m curious why Ford had issues with their diffs... were they perhaps using marginally sized differentials? Do bigger rings and pinions make up this and allow thinner oil comparatively? A lot of questions going through my head but I’m not an engineer

 

[userfriendly]

Hmm... so on an unrelated note we have a Chevy 2500HD diesel and the manual called for 75w90 in the differentials which I thought was interesting as it’s rather light. I was under the impression heavy duty trucks used 75w140. But not working on big trucks for a living and knowing 75w90 is typically your standard I went with it anyways. We use this truck to haul horses around. Now I’m wondering if I should have used 75w140 or even maybe 110. It’s a 2015 model so it’s past the classification changes you guys mention so in theory the engineers should have accounted for it when they speced the fluids. I’m curious why Ford had issues with their diffs... were they perhaps using marginally sized differentials? Do bigger rings and pinions make up this and allow thinner oil comparatively? A lot of questions going through my head but I’m not an engineer

I switched all 1500s, 2500, and 3500s to 80w140 synthetic. Good to -35. The last 2 pails were Petro-Canada and Chevron.