200 Hp Merc Water Temp Alarm

[LCheap]

Open to suggestions, I have a 1984 200Hp Mercury that gives me a high temp alarm at 3000 rpm under load, not with muffs, I have changed the water pump, thermostats and popit valve and still have the same problem, also when the alarm goes off I loose water pressure and water stops pumping from the weep hole. I have back flushed water through the thermostat and popit valve openings and water flows so I am lost, this all started after I had the impeller replaced by a boat repair shop. Could the new impeller be bad? Please if anyone has any suggestions on what to try next please advise.
Thank You!
LCheap

 

[BullyARed]

Re: 200 Hp Merc Water Temp Alarm

If you have changed the thermostat and water pump and if the water came out from the weep hole normal at idle speed, check the impeller then it could be the temp alarm sensor itself. When the alarm goes off, the motor is shutting/slowing down gradually. I had this similar problem with my Suzuki outboard and had to replace the sensor.

 

[j_martin]

Re: 200 Hp Merc Water Temp Alarm

What's your WOT rpm. If it's low, you might be overloading the engine, even at half throttle.

hope it helps
John