John Esposito at quantumechanics.com says that detergent oils should not
be used in an OD because they foam.
Is there a reason why a modern detergent oil would foam in a gear box
but not in an engine? Or do they in fact foam in an engine as well, but
it matters in a gear box but not the engine?
Don Malling
Glenn Coughenour wrote:
> The simple explanation is that the Gear Oil ratings and the Engine Oil
> ratings are on different bases. Dave is correct about some of the
> temperatures used. The numbers in the ratings are not proportional to the
> viscosity, i.e. SAE 90 gear oil does have about the same viscosity at 100
> deg C as SAE 30 engine oil. The additive packages are designed for
> completely different issues, that is the big difference. Current day engine
> oils are probably not great for gear systems because they have detergents
> that enhance foaming in a gearbox. In the '50s and '60s, the differences
> were not as great and you could readily purchase non-detergent engine oil.
>
> The "W" rating, by the way refers to the oil performance when cold. One
> should focus on the second number to choose an oil for expected normal
> operating temperature, look at the "W" number depending on your climate.
> Our friend in Nova Scotia obviously needed a low one this week, while the
> Florida TR drivers do not. [The guy in Nova Scotia probably doesn't need
> bug spray in his glovebox though.]
>
> Glenn C
> 1959 TR3A TS31684L [in total frame up restoration]
> 1960 TR3A TS64803L [driving, but needs work]
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