Overheat Buzzer goes on / off

[nhmaina]

I just purchased a used 14' boat with a johnson 40HP sea nymph (1984). I took it out for the first time yesterday. I am not a motor expert by any means. Anyway, the overheat buzzer appears to go on after about 4 minutes in the water, then it stays on for another 2-3 minutes before going back off and staying off until I turn off the motor and restart. Then it does the same cycle. The stream coming from the top of the motor is warm but not hot by any means. I can't say it's really strong though either. At idle it lands about 16 inches from the motor (in the water). Any ideas? Did I hurt the motor? I took off the top cover and the large round gear on the top was hot to the touch. Finally, the one time it didn't make a sound was when I was the only one in the boat, so the boat was higher in the water. Speed didn't effect if the buzzer went off. Sorry for asking such a long question on my first time in the forum.

[boats.net]

Probably need to replace water pump and check thermostat.