Mercury 150 overheat Alarm

[Loneshark]

My Mercury 150 overheat alarm (constant) is going off and I would like a few suggestions on what may be causing the problem.

Here is what is happening.

I ran the boat for 20 minutes this weekend for the first time this year. Everything ran great until I got back to the dock. I pull up to the dock and as I am going up to the bow to tie off. The alarm goes off. I Look at the motor and it was still pissing. I turn the motor off and immediatley restart and the alarm starts going off again. So I turn it off. Then restart the motor a second time and no alarm.

The same thing happened at the end of last year so I changed the water pump before puttting the boat up for winter. Ran it once with no occurance and thought changing the water pump fixed the problem but apparently I was wrong. LOL.

Any ideas or suggestions would be appreciated?