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Discussion Starter · #1 ·
Hello,

could someone guide me on what type of differential oil the Brooklands non Turbo uses? I am guessing regular 75W-90, any idea if this is correct?

Thanks

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I'd go with EP 85W-140, which is one of the options.

See Chapter D of IETIS, it gives a long list of options from multiple brands for the final drive unit (AKA differential).
 

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Personally I use 80 W 90, which I consider a good compromise.

.....W140 is indeed a very high viscosity warm, in my opinion too much

80 W 90 or 85 W 90 is a medium recommandation for all countries, maybe except for high outside temperature such in Middle east
 

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.....W140 is indeed a very high viscosity warm, in my opinion too much
For this application, I'm of the mind "more is better" when it comes to warm viscosity. That being said, I have never seen as wide a range of options as are presented by Crewe for this specific application, and without any explanation (that I was able to find, anyway) for choosing among them.

Your choice is certainly one of those listed. EP gear oil is essential for this application.
 

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Discussion Starter · #5 ·
I'd go with EP 85W-140, which is one of the options.

See Chapter D of IETIS, it gives a long list of options from multiple brands for the final drive unit (AKA differential).
Great, thank you very much.

Can I find this on the rrtech website?



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No need to go higher than 90wt. Castrol 70-90 The data you need is in the owners manual and every workshop manual, the latter is available online.
 

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every workshop manual, the latter is available online.
Not for the 1990 and later cars, at least not through "official channels." Bentley has yet to make IETIS available for the 1990 and later cars. There are tons of bootleg copies out there, though.

From TSD4700, which shows the same thing as IETIS for the later cars:
29701
 

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I agree the range is indeed very large, too large in my opinion, maybe unclear
Mercedes for example is clear, 85 W 90 , thats all.
I think in the owners manual, it is a bit clearer for late SZ .

The problem with a too hig grade is that before the oil get warm and at high temperature for best lubrification, you may be back in your parking .

I mean that on short drive, oil will be too viscous and think and lubricating properties will not be optimum, because a W140 grade is for high temp oil , above a ....W90 grade.

Important point for car driven usually reasonnably, this is why ...W140 is in my opinion not adapted, except if you drive very fast.
 

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I'm sorry, @Jean7, but you really misunderstand how multi-viscosity oils work.

The viscosity is, for all practical intents and purposes, on a "sliding scale" from the low number when the oil is cold to the high number when the oil is hot. As it warms, it's somewhere in between. It doesn't go from 85W equivalent when dead cold to 140W equivalent after a few short miles. It needs to heat up quite a bit before reaching that weight equivalent. Then one must also take into account that "hot" oil of a significantly higher weight value is actually less viscous when hot than significantly lower weight oil is when cold. I'd be shocked if hot 140W equivalent is more viscous than 85W dead cold is.

But, in any case, one can and should choose whatever one is comfortable with in the range of EP oils that Crewe originally specified. If 85W-140 makes you (the generic you) uncomfortable, then don't use it. Either use one of the 80/85W-90 or straight 80 or 90 weight EP oils.
 

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Humm, not sure I missunderstand....but I might not express well what I understood and have studied with some people who knew well the topic, being in the automotive oil production.

According to Society of AUtomotive Engineers, first number before W is viscosity cold, second number is viscosity hot.

At same hot temperature, when the final drive is warm, .... W90 will be more fluid than ...W140, this is what I meant.
As a matter of fact, oil efficiency is based on some part on viscosity. The oil lubrication properties are depending on oil temperature. ....W140 will be for sure more protective at higher temp, but it is supposed to be less protective at lower temp.
I understand you disagree with this theory, but this is the theory of some engineers from french company MOTUL I met several time.
Each oil is made for a particular duty and and range of temperature.
Same for engine oil, 5W 40 will be fluid at starting and protect fast , 15W40 will be more thick at starting and will need more time to have its full properties.
Some companies for example are reluctant advising 10 W 60 for some engine, because they consider that in normal use, tha warm grade W60 will be never reach so the oil properties will not be optimum as it is conceived for high temp or cars with turbo.
This is an engineer point of view that I totally share. "More is better" is not adapted to all cases as you may have in fact oil not adapted to the real use conditions, which means not benefiting from all the oil properties/ protection.
 
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