I'm with Tiny, any oil gets thinner with temp, as stated in the wiki article: "The viscosity of a multi-grade oil still varies logarithmically with temperature"
Bill
Yes, that is correct.
A 10W-30 oil gets thinner when warm.
"The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened." I'd have to see a viscosity table to see if a 20W-20 oil (if there is such a thing) gets thinner when warm.
Tiny referred to a 10-30 oil but I took him to mean 10W-30.
Shell-Rotella and Castrol are working on (selling?) a 0W-30 oil for fuel economy, but very tight bearing clearances are needed to maintain oil pressure.