Originally Posted By: NH73
It seems what you are indicating is the higher the viscosity the higher your oil temp. Is this is what you are trying to say or what?
For the two data points, the second of which I deliberately chose the thickest off the shelf oil I could get (now I've got 600ml and absolutely nothing to do with it).
Think of the oil in the sump of the Briggs, getting "worked against" by the crank/bearings....it's thicker, there will be more viscous friction, and more energy put into the oil...the combustion side is not a biggie typically, if you hook an engine up to an electric motor, it will get to nearly operating temperature without fuel.
The oil then has to be splashed against the crankcase to transfer its heat into the environment...more heat to dissipate, oil has to run hotter to drive the heat away.
More viscosity equals more work against the oil, and greater film thicknesses (more parts separation).
20W60 was, as I said, an extreme to bookend my measurements, not a recommendation, or what I run.