87 Johnson 40hp Overheat alarm

[Bassbuggy]

My overheating alarm goes off after 5min’s at the dock or if I’m going threw a no wake zone. I’ve replaced my t-stat & it’s still doing it. If I speed up it goes off. My tell-tale is working excellent. Does anyone have any ideas?<br />Also what is the thing that is the size of a cork but looks like clear silicone, & has a brown wire in the center of it, & it goes into the head by the top sparkplug? Is that my temp sensor?

 

[mikeyzx2]

Re: 87 Johnson 40hp Overheat alarm

yep that's your temp sensor, looks like it's glued in, mine is a brownish tan wire too. supposedly has some sort of wax or something in it that melts if it gets too hot and closes the circuit

 

[OBJ]

Re: 87 Johnson 40hp Overheat alarm

Welcome Bassbuggy!<br /><br />You have the typical symptoms of a worn out water pump impeller. The "fins" on the impeller have taken set and don't pump as good at low speeds as they do at high speeds. Drop the lower unit and pull the impeller out...betcha all the fins are bent round.

 

[Bassbuggy]

Re: 87 Johnson 40hp Overheat alarm

The dealer told me that if it's pissing fine then the pump was ok.<br /><br />Thanks OBJ,<br />I just wanted to make sure before I start going in the wrong direction with it.<br />Is their anything that I need to watch out for when I drop the lower unit.<br /><br />Again thanks

 

[OBJ]

Re: 87 Johnson 40hp Overheat alarm

Nothing I can think of buggy. You'll have to disconnect the shift rod....usually the hardest part part of the job. Are you familiar with this?<br /><br />If you don't know when the impeller was changed out last, might be a good idea to just put a whole kit in....housing and all.