Was thinking on this one just a bit the other day because I also see my average temp creeping up above my stats temp ever so slightly as summer water temps peak, but here, where I mainly boat it tops out around 70 F.
When the water is cold cold, like in the 30's, 40's, the motor runs at thermostat temps of course, which is around 140'ish F, but water now is around 70 F and I always see 150'ish F......Motor running temp is(also) definitely a function of coolant temp!!
So, say we live in a perfect linear world and we have a nice straight line for an equation, your volume of cooling flow/sec, motor age(wear/hrs), size, internal combustion temps, friction, etc., etc are all roughly the same as mine(or close anyway, 1992 175 carb.) and my motor is in perfect working order as is yours......
Then if we use my motor and lake as a baseline, 150/70 = 2.143, which then is a constant(a scalar) for a ratio of the normal(not hose) running/loaded at speed engine temp to water temp of 2.143:1 for engine temps above stat temps due to higher lake(guessing and appears to be above 70'ish F) coolant temps.
then at 90 F, you should run at 90*2.143 = 193 degrees F.
Just a theory.......Should be happening w others though, perhaps someone will chime in and confirm or debunk. IDK, I've never ran in 80/90 F waters.
However, the/a engine has to heat up/run hotter if we hold fixed parameters as above and run in higher coolant temps........Think about it this way, drop the motor in say 150 F water and run, I bet she'd run 300+ F , for a short while anyway
and will always attempt to approach the source temp of the fire burning(and/or fiction, which ever is highest) in the cylinders as coolant temps increase.
The floor/running temp is limited to the and a function of stats closing temp, but the ceiling/running temp is a primary function of varying coolant temps, fixed'ish combustion temp and the fixed'ish volume(stats open, poppet open and impeller volume and rate at WOT) of water moved through the motor.
