Overheating Alarm

[Savage Mako]

My motor is a 96 90hp mercury outboard. A copuple of years ago at WOT the temp alarm went off. The dealer suggested the poppet valve needed replacing as the motor had been serviced and impeller changed, this was done and no problem until recently.<br /><br />During the christmas holiday I ended up on a sand bank and even though the motor was trimmed out, a lot of sand and weed was being churned up.Since then at about 4900-5000 rpm the temp alarm is partially comming on, below this all seems OK. I had the impeller changed thermostat cheked etc but still doing it. I have noticed that if I open the throttle to more than 5000rpm the alarm will fully sound and the motor seems to die.<br /><br />The mechanic said he did not think my motor had an overheat saftey system that causes it to make the motor run at lower rpm. Is this right?<br /><br />Has anybody got any suggestion on whether they think it is the poppet valve thermostat,sender unit or maybe even something else. Any suggestion on the best test to do first. The telltale has a strong constant streem of water.<br /><br />I also notice that there are three holes below the cowl handle, these appear to be an outlet for water/exhaust looks like where water might come out once thermostat opens, I dont remember ever seeing either any or much water comming out from here. Is it supposed to?<br /><br />Thanks

 

[mellowyellow]

Re: Overheating Alarm

welcome aboard,<br />sounds like you have a partially clogged cooling<br />system caused when you sucked in the sand/kelp.<br />I would remove the lower unit and inspect all<br />passages for blockage. test proceedure for alarm<br />is in service manual. make sure it is working<br />properly.<br />good luck,<br />M.Y.

 

[KCLOST]

Re: Overheating Alarm

When the poppet opens at higher rpms you will see water exiting the upper exhaust ports (the holes below the cowl handle). If you are not seeing any water exit (again at higher rpms (I think above 3000) you have a poppet valve problem. Someone should be able to confirm when it opens... Don't try to find out using ear muffs, you might damage the engine...<br /><br />It may just be clogged with crap. Easy to check and even replace as you've done it before. Try that first. You may want to flush the system from the poppet hole also, to help get some of that stuff out of there.

 

[Kenny Bush]

Re: Overheating Alarm

Also you may want to check the water passages in the head. Some crap, and even pieces of the impellar will make its way up into the head.