Got a quick question. I am running a 160 thermostat in my supercharged 5.3 airboat. The radiator sits about 7 inches away from my 80 inch diameter prop. On the water pump I have the 5/8 heater hose nipple capped and the 3/4 inch nipple has a 3/4 heater hose attached that goes above the motor to a resevoir where we remote fill etc. since the radiator is below the engine.

While cruising and running my engine temp stays dead nuts at 161. But when idleing for a while the temp will creep up to 200 or so usually I am back to getting on plane before it rises higher than 210. Doesnt overheat or anything like that and if I idle at say 1500 to 1700 rpms the coolant temp comes right down to 161. It doesnt appear to be a fan issue, since I have a huge prop pulling air through radiator.

It appears to be a flow issue when idleing at low rpms. You can feel the intake hose going to thermostat and it is significantly cooler than the output hose at idle.

What modifications can i do to the thermostat to let more flow at idle? Drill holes? BB mod?

Any thoughts or suggestions would be greatly appreciated.