retired,
The value you quoted i.e. 99 is the viscosity index NOT the viscosity. The actual viscosity (kinematic at 40 C.) is 32 for Tellus 32 and 22 for Bartran 22. The numbers refer to the value in centi Stokes for each oil and is the value that most people would refer to as the viscosity. Obviously being a "thinner" oil 22 may cause you problems particularly in a warmer operating environment.
I’m not an oily type so someone who is, may want to jump in with a more detailed explanation.
There are various cross-references available on the web but as a rule of thumb use like for like viscosity numbers e.g. Hyspin 32-Tellus 32-Ecoterra 32 etc, the name only being a brand.
Cheers
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