My 4-108 would slowly overheat if I ran continously above 2500 RPM.
Tried a bunch of things but concluded that the heat exchanger was too small or the raw-water intake was too small.
Either way, no big deal as my normal cruise
power was 2100 RPM.
I could run @ 2400 all day long.
Also 5-10 minutes at 3000 if needed to make a bridge and 4000 Available for emergencies.
No big deal in my case, never tried to spend money buying
a bigger heat exchanger.
Tried the easy stuff, acid boiling heat exchanger and oil
cooler, new thermostat, new impeller, flush and replace coolant, new hoses, new cap, etc. Probably $200 total.