I think with a closed system the closer to what would be a normal automotive engine temp the better, a 160 stat in that system will usually run from 160-180* but because it’s a pressurized system it won’t cause localized boiling like it could in an open system. The benefits of warmer running are less water condensation and less fuel dilution in the oil. These are both issues for certain 4 stroke outboards that “make” oil but what it really is happening is water & fuel aren’t burning off in the motor oil. I have experimented with both a 140 and 160 stat in the open cooling in salt water and I found that the 140 took forever to warm up and even after many years of running a 160 here I did not see any significant amounts of mineral build up when I took the heads off 7 years ago. The only place where I saw anything was was the blocked off cyl head ports at the rear of the intake. So at least here in coastal LI I will stick with the 160 & do a de scaling if necessary. My oil analyses show no water or fuel contamination.
