[madmaxx]

The reason your buddies boat has a 140f thermostat is so the water passages do not plug with salt from salt water. If he had a 200f thermostat then the water would evaporate and the block cooling passages would plug off. True engine longevity may not be as long but most boat engines corrode out long before they wear out. Another thing to remember is a boat engine never gets a break, it never coast, sits at a light etc and most are run close to wide open throttle the majority of the time. I have mercruiser and its therostat is also 140F. Now if you go with larger more expensive engines they will have an exchanger where the engine coolant is run at 200F and the sea water cools the opposiste side of the exchanger. Needless to say you have to take apart your exchanger every couple of years to clean.