[jclark003]

It may be poor raw water flow from a restriction that doesn’t present problems when pressure is high (higher rpm). if you haven’t done so clean and inspect the raw water side of the heat exchanger. Old impeller pieces and or barnacles can limit water flow and heat rejection. Also you want to check your risers. Rust and debris can get lodged in there and prevent raw water flow.

IR temp guns are cheap and can tell you a lot without disassembling half the engine. Check both motors at different places in the cooling loop and look for dissimilar readings or abnormally high temperatures.