75W90 vs 80W90

[Winston]

So, my manual recommends 75W90 GL-4 for my transfer case and 80W90 GL-5 for my differentials. Why do they bother to make a distinction between 75W and 80W designations? The 80W90 oil (Sta-Lube) says it is GL-4 and GL-5 compatible. Why would the manual be so picky?

 

[bruce381]

75W has a much lower "pour point" -40C versus
-25C for the 80W. Maybe the transfer case has to have more bearing protection than than the rear axle.

bruce

 

[MolaKule]

You might try our MTL-R (75W90, GL4/GL5) for your transfer case and HDS-5 in the 75W90 flavor for your diffy.

Engineers who spec oil generally aren't aware of the fine distinctions of lubricants.

 

[bruce381]

quote:

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Originally posted by MolaKule:
You might try our MTL-R (75W90, GL4/GL5) for your transfer case and HDS-5 in the 75W90 flavor for your diffy.

Engineers who spec oil generally aren't aware of the fine distinctions of lubricants.

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Also to add the advancements and improvements made
routinley to lubricants where multi functional products can now be used.
bruce

 

[Islandvic]

is this in the Monty?

 

[Winston]

Thanks for the responses. I thought it was a good general question, since I am sure that my 4x4 is not the only one that has these slight differences in oil spec for each component. I think the key answer was in this statement;

quote:

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Also to add the advancements and improvements made
routinley to lubricants where multi functional products can now be used.

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Sounds like the multifunction fluid I used is OK for both. Obviously where I live, it does not see very cold temperatures.

quote:

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is this in the Monty?

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Yes.

 

[salesrep]

"Engineers who spec oil generally aren't aware of the fine distinctions of lubricants."
How comforting.

 

[TooSlick]

The conventional 80w-90 grade was thought to have better high temp stability, compared to the early 75w-90's and was customarily recommended for differentials. If you go back even further, you'll find straight 90wt being recommended instead of 80w-90.

As for the transfer case, these are often engaged only in cold weather for traction in snow. Hence the 75w-90 spec is typically used....

The gear tooth contact loads in transfer cases are lower than in hypoid diffs, hence they can get by with GL-4 or even ATF is some instances.

 

[sagaboy]

My stock 40 year old 1500 vw bug was using straight 90wt dino oil and when I changed it to GL4 75/90 synthetic my idling speed went-up 300 RPM and shifting of gears was never better than when new

 

[Winston]

quote:

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The conventional 80w-90 grade was thought to have better high temp stability, compared to the early 75w-90's and was customarily recommended for differentials.

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Ah Ha! Same as the reason for the 5W30 winter and 10W30 summer recommendations for engine oil.