I've never run a T-stat in a raw water cooled motor. Nor would I. I wouldn't mind if Rexone set me straight here, but I think restricting the water flow at the end of the cycle through the motor seems less than desireable to me. If you get junk from the lake into your system (weeds, sand etc.) I wouldn't want to put a restriction there.
Besides, I see it over and over again. The temp is not accurate in a open system. If you want to compare to a closed system, your oil temp is a much better guage. If your temp guage is showing 140 deg, it's not the same as a closed system. All that means is that the water heated up from lake temp (around 80 deg lets say) to 140 deg. In a closed system the water is not 80 deg entering in the motor. Probably more like 120-130 depending. Your water temp guage in a raw water system should serve nothing more than a comparison to what it usually runs. The actual number doesn't mean crap. There is no comparison to a car water temp. :argue: Setting a Jetboat to run 180 water temp will probably lead to unnecessary flash boiling in the heads around the combustion chamber. I see no point.
If you think your motor is running too cool, adjust by the oil temp, not the water temp.
,
I suppose that if you run a strainer, bypass valve, and T-stat, it could work, but there is no antifreeze/boil to help protect from flash boiling. Keeping the water in the motor long enough to heat it up to 180 º (thus restricting flow) I'd think would only lead to more likelyhood of flash steaming in the heads. That T-stat will never open up as far as it would in a closed system because it has to keep the water in the motor much longer. It has to heat up the water 100º or more instead of 20-30º like it does in a car or in a closed marine set up. That means the water sits around the combustion chamber longer, with less flow to move the steam pockets.
I'd be willing to bet that if you get your lake water temp up to 180º showing on your temp guage, you are dangerously close to pre-detonation. Keep an eye for little black spots on your spark plug insulators, and good luck.
Just my .02
Nick
BTW, you guys that are running a raw water system and get water temp readings of 180º, what's your oil temp running? Just curious. Would like to know if I'm way off base here.