I ran a little test on stock motor Rhinos since on 3 forums, several dealers and several engine builders could not absolutely say what is normal oil temp for Rhinos are. I ran 3 stock rhinos with stock oil coolers and radiators and found that under heavy load in temps of 100 to 105 Rhinos with stock radiators ran approx 320 to 350 degrees. The water temps were consistently 210 to 220. My Rhino ran 300 but no higher with a 760 Weller motor and size able aftermarket oil cooler with large fan. Are these temps over time engine killers, Yes. Yamalube becomes less effective if exposed to high temps for long period of time. Which can lead to engine part failures (crank, rod, cases etc...). Switching to a synth oil like Amsoil will lower the temp and improve engine protection in these single cylinder motors. But the best improvement would be to add an aftermarket oil cooler and synth oil as well. Doing this will definitely improve the life span of these motors and help prevent engine part failure.