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Comment from another forum below.
Personally I would be ok with another quality manufacturers oil - Millers, Mobil, Shell etc. that actually met the spec and hopefully exceeded it, but going with the VP stuff is mainly an easy way to get it right.
Key point here is that the spec defines minimums: manufacturers can and do produce products that exceed the minimums.
When a lower unit for a DP-H costs £4850, I'm ok with spending a little extra for an oil that exceeds those minimums.
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There are really two ways to think about this and they can never be reconciled -- you just have to decide which camp you join. One school of thought says that the API (American Petroleum Institute) standards are designed to ensure that lubricating oils have a specific set of performance characteristics and so anything that has the same API grade as the Volvo oil should be perfectly acceptable (and cannot lead to refusal to honor a warranty claim). GL-5 is the severe duty rating for gear oils and is very commonly specified for differentials and other auto and truck components.
If you think that way, look at the Volvo gear lube container -- it will say API GL-5 with the viscosity rating 75W-140. There are many other brands meeting those specifications such as Mobil or Red Line that will have the same API classification. Any of those brands should be suitable replacements since the entire point of the API standards is just that -- to ensure that customers can know which oil is deemed suitable by the manufacturer for the service requirement and use any brand of oil they choose that has the same API classification.
The other school of thought is the "why take a chance" point of view. The API standards are minimums -- nothing stops a manufacturer from specifying an additive package that goes beyond what is required to get the API rating. Volvo is not in the oil refining business. They went to a refiner (Shell, Exxon or the like) and said "produce gear oil for me that has these specifications and put it in these containers with my label on it." The great mystery is whether Volvo just said "make us API GL-5 75W140" or whether their additive specification is different. We know the Volvo gear oil is GL-5 because the API would not allow that to be on the label if it had not been tested to meet the standard. If you use a brand other than Volvo, you are betting that Volvo has not included other additives that may give their oil better properties for their gear sets. There is just no way of knowing this unless someone who actually knows spills the beans -- and you can be sure they won't. Personally, I doubt whether the Volvo packaged gear oil is really any different than the other full synthetic GL-5 75W140 oils. The cost difference is probably due primarily to higher profit margins and the expense of branding it and running a separate distribution channel through the Volvo dealers.
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Personally I would be ok with another quality manufacturers oil - Millers, Mobil, Shell etc. that actually met the spec and hopefully exceeded it, but going with the VP stuff is mainly an easy way to get it right.
Key point here is that the spec defines minimums: manufacturers can and do produce products that exceed the minimums.
When a lower unit for a DP-H costs £4850, I'm ok with spending a little extra for an oil that exceeds those minimums.
--------------
There are really two ways to think about this and they can never be reconciled -- you just have to decide which camp you join. One school of thought says that the API (American Petroleum Institute) standards are designed to ensure that lubricating oils have a specific set of performance characteristics and so anything that has the same API grade as the Volvo oil should be perfectly acceptable (and cannot lead to refusal to honor a warranty claim). GL-5 is the severe duty rating for gear oils and is very commonly specified for differentials and other auto and truck components.
If you think that way, look at the Volvo gear lube container -- it will say API GL-5 with the viscosity rating 75W-140. There are many other brands meeting those specifications such as Mobil or Red Line that will have the same API classification. Any of those brands should be suitable replacements since the entire point of the API standards is just that -- to ensure that customers can know which oil is deemed suitable by the manufacturer for the service requirement and use any brand of oil they choose that has the same API classification.
The other school of thought is the "why take a chance" point of view. The API standards are minimums -- nothing stops a manufacturer from specifying an additive package that goes beyond what is required to get the API rating. Volvo is not in the oil refining business. They went to a refiner (Shell, Exxon or the like) and said "produce gear oil for me that has these specifications and put it in these containers with my label on it." The great mystery is whether Volvo just said "make us API GL-5 75W140" or whether their additive specification is different. We know the Volvo gear oil is GL-5 because the API would not allow that to be on the label if it had not been tested to meet the standard. If you use a brand other than Volvo, you are betting that Volvo has not included other additives that may give their oil better properties for their gear sets. There is just no way of knowing this unless someone who actually knows spills the beans -- and you can be sure they won't. Personally, I doubt whether the Volvo packaged gear oil is really any different than the other full synthetic GL-5 75W140 oils. The cost difference is probably due primarily to higher profit margins and the expense of branding it and running a separate distribution channel through the Volvo dealers.
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