I do notice higher oil and coolant temps with thicker oils in certain engines. Specifically higher coolant temps on my father’s 2018 ND Miata, with the 2.0 skyactive, I always put in Valvoline advanced 0w20 at every oil change for him. One day we tried using some Valvoline advanced 5w30 just to try it out. We used it in the summer, thinking it would be better for the hot summer months, which it really isn’t, because main bearing clearances are 0.0007-0.0015.
Cars got 55,000miles now. Tried running 5w30 at 40,000 miles for 5k miles until we hit 45,000 miles.
Coolant gauge display is on a screen in the gauge cluster. With 0w20, the screen needle always sits below 210, probably more like 195-200 even in stop and go traffic in the hottest days in South Carolina. With 5w30, we noticed the needle staying at 210 in city driving, and very slightly higher than 210 in stop and go traffic. This never happens with 0w20. It always sits below 210, probably 195-200, even in stop and go traffic in hot South Carolina.
This was consistent during the 5k miles of 5w30 use. Then we switched back to 0w20, and the coolant gauge needle never ever touches 210.
Based on the skyactive 2.0’s factory main bearing clearance of 0.0007-0.0015, 0w20 should be more than adequate for daily driving for this particular engine especially with oil pressures that are on the high side compared to many other modern engines that run lower oil pressures during idle.