Overheating Alarm on 1990 Mercury 115 HP

[epperlyr]

I have the Overheating alarm going off some times but the Temp guage shows everything is normal. I can see the Thermostat open and the temp go down on the gauge, It apears to open around 140 deg. It all works fine in the drive way with the water hooked up but out on the lake for a couple of hours and it will start going off. There is a good stream of water coming from the tale tale and if the alarm goes off you can speed up to over 3200 rpms and it stops. Please advise the next step.

 

[fishonboat]

Re: Overheating Alarm on 1990 Mercury 115 HP

When was the last time you replaced your water pump. You may be pumping water out of your tell tell but that dosen't mean your getting enough water. If the impeller is worn it may still pump but it's not very efficient. This is an easy job and costs about $20 to $50 dollars if you do it yourself. You may also want to check the poppet valve(pressure relief valve).