Overheat buzzer on 40 Merc

[BNelson]

Hi<br />I've got a 1991 40hp Merc and getting overheat buzzer(continuous,sometimes sputtering) after about 15 min of moderate use. The tell-tale is a little limp at idle. It seems to work fine underway and the water from it is on the hot side but no steam. The impeller was changed in 99 and the motor may have five or six hours on it after impeller change. A mechanic changed the ignition after testing the module and finding it ok. He ran the motor for about 10 min. and no buzzer. I bought the boat trusting it was fixed and still get the buzzer. I've searched the archives and found 3 possibilities. Impeller, Thermostat or Sending unit from oil injector. Just wondering if anyone could tell me where to start. Also, when the mechanic said "module" was he talking about the sending unit or the buzzer itself?<br />Thanks for any help,<br />Bruce

 

[sharkcat]

Re: Overheat buzzer on 40 Merc

Hi Brewster on motors that arent used much it is probably more important to regularly change/inspect the water pump components if they dont turn very often the impeller can set in a position & not work to well at all speeds.On mercs a continuous beep is overheating An intermittent beep is oil either low level or oil injection failing.If the tell tale stream is weak at idle check for blockages in the cooling system them remove,inspect & replace all worn parts in the water pump also check the thermostat & poppet valve if fitted, a new water pump is a lot cheaper than a new powerhead Hope this helps

 

[sharkcat]

Re: Overheat buzzer on 40 Merc

Hey Brewster Ive just realized you are my 200th post..I hope you feel special