2001 Merc 150 hp overheating

I just happened to feel the water comming out of the motor while rinsing in a lake the other day and it was hot. I've had the boat for 3 years and have it tuned every year. Last autumn I had the impeller replaced. I do not have a temp gauge or a pressure gauge just an overheat alarm. (which has never gone off) the motor is a carburated 2 cycle. The water wouldn't burn but it's pretty hot (like hot tub hot). It does seem to cool off just a little when the boat is traveling over 5kts. (no tach either) The motor "pees" normal, barely spits when cold then pees well after that. My question is, would 140-160 be a normal temp for the pee if the thermostat doesn't open until about there? I guess I don't know if hot pee is normal or not.
but since it does start to cool at speed, it sounds like a thermostat is stuck closed. would you agree?


thank you
dw

Re: 2001 Merc 150 overheating

looking at the service record reveals that both thermostats were replaced last autumn with the impeller. What also evades me is why, when flushing through the powerhead, the discharge is always cool. (When I rinse in a lake I run it about the same amount of time) I use the boat offshore between 10 and 35 miles but rinse the salt out after every trip. the manual says the overheating alarm sounds at temps over 210. Clearly near boiling discharge would injure a hand and this just ain't that hot.

Re: 2001 Merc 150 overheating

Everything is normal. When flushing with the hose you are forcing water thru the motor at a higer rate than the impeller does at idle.

Re: 2001 Merc 150 overheating

Thanks for that! I worry until the fish show up, then I fear I don't worry enough.