Excellent suggestions for looking at causes of overheating on any engine! However start even lower in the system: we are hearing of lots of marine growth--check the through hulls and outer strainers for growth. I often put a "T" on the top of the through hull, so I can "Rod" the thru hull by removing the cap in the top of the "T", the engine intake goes off the right angle. (also this can be used as a pick up for bilge pump or putting antifreeze into the raw water system, with the through hull closed) Back flushing the system with a garden hose is excellent. Once i got a gargage bag caught part way into the intake hose, through hull was clear, pump was clear. Yesterday my Air conditioner cut off--over heat. There was cooling water flow, but it seem low.. I cleaned the strainer, little debris, but the flow into the unit when I opened the thru hull with the top off seemed weak. I back flushed it with the garden hose, with little improvement. Then I turned the pump back on (next step was to dive on the thru hull) and all of a sudden "slurp" a 3 1/2" long fish came into the strainer--a bit worse for the wear! I removed the dead fish and voila! all was well. I suspect that my diver knocked off the outside strainer when cleaning the bottom last week. I will have to watch it until I haul next time. This is not the first time I have had a fish caught in the thru hull. Bob Austin Symbol 42 Pensacola, FL