Jo9hnson 70 HP (Mid '80's vintage) overheating
 

I have a mid '80's vintage Johnson 70 HP outboard. When I put the boat
in a week ago, the buzzer went off after idling and running at low
speed for 5 - 10 minutes. Looking in a manual that I have, it appears
to be overheating. I tried it again over the weekend, and as soon as I
opened it up, the buzzer came back on. Looking in some discussions,
there is talk of water pumps and thermostats. The manual describes
replacing the pump, in fact recommending replacing the pump with an
improved version. I can't find anything in the manual about a
thermostat. Is there a thermostat on this motor and where is it? Any
recommendations on where to buy parts?

Thanks