Older Gears in Transfer Case and Diffs Need Thicker Fluid?

[SONICMASD]

I had a customer ask me a question today that I didn't know the answer to so I figured here would be a good place to ask.

In a transfer case or differential that has high mileage, say 250,000 or more, would it make sense to go with a thicker gear oil?

So say the manual says both 75W-85 and 75W-90 are in spec, is it right to assume that gears with that high of mileage will have more wear on them and that a thicker oil could help them run cooler and quieter?

I know those 2 options are not oceans apart but one has to go in the vehicle, so which one and why?

 

[OilUzer]

Good question. I guess using thicker engine oil theory (for high mileage cars) is to reduce leaks/seeps, burning, etc. which may not necessarily apply to the gear oil.

 

[SoNic67]

The "numbers" of those fluids mean little because of wide range of viscosities that mean that "85" or "90". This is table that I made and posted somewhere else, I didn't actually include any 85 there, but the idea is that the "90" are not equal in viscosity and the "85" might be equal to some of those.
For Lucas Synthetic 80W-85 the cSt@40C=98 and the cSt@100C=14.4

Thicker oil is actually not fixing bigger gaps, because those gears are lubricating by splashing, not by a pump (engine, transmission).
Thicker oil is good in higher ambient temperatures (and load generated temperatures) because it keeps the film between them, by "sticking" to metal, not by pressure.
That protection needs to be there before actual wear happens.

Sure, if you put something really thick in there (honey-line) it will attenuate the noise, but the mechanical vibration and erosion is still in there.

I did have good experience with an additive that is supposed to repair the metal, noise abated without thicker oils, but that was just my experience. Not sure if it will apply to everyone, I am not a paid reviewer or anything:

TriboTEX Transmission Treatments

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shop.tribotex.com

 

[benjy]

i like + use REAL synthetic Redline gear lubes as a real synthetic thickens LESS in cold + thins LESS in heat + therefor protects more!! i leave the formulation to the PROS!! today manufacturers are specing thinner lubes EVERYWHERE, BUT IMO mostly looking for minute mpg improvements in exchange for less longevity + once warranty is gone its your $$$$$

 

[ka9mnx]

It's the reason I use 75w-140 (SuperTech Synthetic) in my F150 (255k miles) and my 4Runner (270k miles). I also use it in my Ranger because when SAE lowered the V@100C for 75w-90 Ford came out with a TSB recommending 75w-140 to replace 75w-90/80. I use it in everything now since I learned about the SAE change (in older vehicles originally spec'd for 75w-90). It's the reason several gear oil manufacturers came out with 75w-110.

 

[JHZR2]

i like + use REAL synthetic Redline gear lubes as a real synthetic thickens LESS in cold + thins LESS in heat + therefor protects more!! i leave the formulation to the PROS!! today manufacturers are specing thinner lubes EVERYWHERE, BUT IMO mostly looking for minute mpg improvements in exchange for less longevity + once warranty is gone its your $$$$$

What exactly is a “REAL” synthetic?

Redline has been some of the worst performing lube I’ve run. In worn differentials noise has returned far faster, so either redline shears, or the add pack depletes quickly.

 

[JavierH19]

i use 140 instead of the recommended 90 in my 310k gmc rear, still going strong. A lot of metal has come off so i can't imagine a thinner gear oil still protecting and making up the difference.

 

[SONICMASD]

It's the reason I use 75w-140 (SuperTech Synthetic) in my F150 (255k miles) and my 4Runner (270k miles). I also use it in my Ranger because when SAE lowered the V@100C for 75w-90 Ford came out with a TSB recommending 75w-140 to replace 75w-90/80. I use it in everything now since I learned about the SAE change (in older vehicles originally spec'd for 75w-90). It's the reason several gear oil manufacturers came out with 75w-110.

When did SAE lower the 75W-90 V rating? I know they split the 75W-90 scale in half in 2005 when they created 75W-110 but that's different than lowering the viscosity measurement. I tried Googling for the Ford TSB about this but didn't find anything either.

 

[SONICMASD]

The "numbers" of those fluids mean little because of wide range of viscosities that mean that "85" or "90". This is table that I made and posted somewhere else, I didn't actually include any 85 there, but the idea is that the "90" are not equal in viscosity and the "85" might be equal to some of those.
For Lucas Synthetic 80W-85 the cSt@40C=98 and the cSt@100C=14.4
View attachment 60815
Thicker oil is actually not fixing bigger gaps, because those gears are lubricating by splashing, not by a pump (engine, transmission).
Thicker oil is good in higher ambient temperatures (and load generated temperatures) because it keeps the film between them, by "sticking" to metal, not by pressure.
That protection needs to be there before actual wear happens.

Sure, if you put something really thick in there (honey-line) it will attenuate the noise, but the mechanical vibration and erosion is still in there.

I did have good experience with an additive that is supposed to repair the metal, noise abated without thicker oils, but that was just my experience. Not sure if it will apply to everyone, I am not a paid reviewer or anything:

TriboTEX Transmission Treatments

Run longer, stronger, and cleaner with nanotech. With our award-winning engine treatments, you can boost performance, use less fuel, and extend the life of your vehicle. Funded by NASA, the Department of Energy, the National Science Foundation, and the U.S. Air Force.

shop.tribotex.com

That's a good point, but I'm referring to choosing between 2 oils from the same manufacturer. For example Redlines's MT-90 is 30% higher viscosity at both 100 and 212 degrees than MT-85. So if you have a transfer case or diff with 250,000 miles on it or more, which one would you go with / does it matter?

 

[ka9mnx]

When did SAE lower the 75W-90 V rating? I know they split the 75W-90 scale in half in 2005 when they created 75W-110 but that's different than lowering the viscosity measurement. I tried Googling for the Ford TSB about this but didn't find anything either.

Early 2000's. It was another energy conserving move. There isn't much information on the internet about it. Here is something I pulled from a paper years ago:

Pre 2001 Specs Post 2001 Specs

@100C @100C

w90 13.5-24 w90 13.5-18.5

w140 32.5-42 w140 24.4-32.5

 

[OilUzer]

I think that's why the number of cars in the junkyard have increased since then.

 

[Job]

Early 2000's. It was another energy conserving move. There isn't much information on the internet about it. Here is something I pulled from a paper years ago:

Pre 2001 Specs Post 2001 Specs

@100C @100C

w90 13.5-24 w90 13.5-18.5

w140 32.5-42 w140 24.4-32.5

All the new 90 will fall within the range of the old 90. The new 140 is always over the old 90 requirement. I don’t think my 96 pickup will suffer too much using the new oils as recommended.

 

[ka9mnx]

All the new 90 will fall within the range of the old 90. The new 140 is always over the old 90 requirement. I don’t think my 96 pickup will suffer too much using the new oils as recommended.

The old 75w-90's I compared were in the upper end of the V@100 range which was cut off by the new specs as was the 75w-140's. I suppose SAE lowered the upper ranges of both specs to increase fuel efficiency. Na, you will be fine with modern 90. I'm just overly cautious and tend to keep my vehicles until one of us reaches our use-by date..

 

[Job]

The old 75w-90's I compared were in the upper end of the V@100 range which was cut off by the new specs as was the 75w-140's. I suppose SAE lowered the upper ranges of both specs to increase fuel efficiency. Na, you will be fine with modern 90. I'm just overly cautious and tend to keep my vehicles until one of us reaches our use-by date..

Since my own use by date is approaching closer my truck will be fine. First it will probably go to a gardener then to the scrap yard. I think it’s great information and you select what you want with deeper knowledge of oils. I can see why they went to the 110 grade for more overlap at the high end, never heard of it before.

 

[SoNic67]

I know they split the 75W-90 scale in half in 2005 when they created 75W-110 but that's different than lowering the viscosity measurement.

All the new 90 will fall within the range of the old 90.

How is that "different"?
Now, recommended oils that before were in 90 scale, are found in 110.
Yes some of lower 90's are still in the 90's. But that's the thinner part of the fluid spec, nobody in auto industry really was going for that when recommending 90, but rather "middle" of the spec.
Because of that, now I use 75W-110 in my 80W-90 specified diff.