Hello everyone. I'm new to this site so please be kind. First post. Merc. Cruiser 302 ford 188 hp. Overheats. The boat normally runs 180 temp. New thermostat and no blockage in raw water system that I can see. Temp alarm went off and the boat was at 230. I could smell the exhaust bellows melting. No major damage. Can a weak/worn impeller cause the mechanical water pump on front of engine to starve the entire motor at cruising speeds? At idle forward the boat is fine. Any speed above 30 is a problem. I'm new to boating and I know it's a simple question but to me it is not. Thank you for any help