Re: Confused about which oil weight to use
Since the engine is not blowing a lot of smoke, your problem is the unexplained overheating. I would investigate all the possible causes before spending many thousands to have the engine removed and rebuilt. The old saying, "If it ain't broke, don't fix it," may apply here. These engines are tough little buggers. Are you absolutely sure it's not just a bad impeller, a blocked sea strainer? Is the pump the right pump? Is the bronze in good condition or maybe worn beyond limits? The water you're seeing coming out of the exhaust may not be adequate. Is there an air leak into the system? Check all the hoses and clamps. Is there an anti-siphon loop letting in air? Look for not-so-obvious small things before jumping. If you can't find the problem and you are not comfortable removing the head yourself, maybe paying a good mechanic for a few hours to further investigate the overheating would be a good first step before spending a lot of money. That missing thermostat is a big clue. It's likely that this is not a new problem.
Alberg 35: With a philosophical flourish Cato throws himself upon his sword; I quietly take to the ship.