1979 Johnson 115, no temp gauge.

[TampaBoater]

So i just bought a 1977 MFG Caprice Bowrider with a 1979 Johnson 115 in very nice shape, but the boat has no temp gauge and I do not feel like taking it out without a temp gauge. I am aware that these motors have a temp switch on each head, wired to a "hot" alarm at the control box, but I am not entire sure this system is working properly, or even at all. I would like to install a temp gauge, but I don't know where I would connect it at the motor to receive signal. Any thoughts?

 

[Bosunsmate]

The tan wire to the rear of each head goes to the overheat sensor. If you follow that wire a few inches back from the head there will be a rubber sleeve. If you slide that along a bit it will expose a connection.
If you disconnect it and then take the end of the wire that comes from the wiring harness and put that to a ground on the engine such as a bolt then the overheat horn should sound so long as the engine ignition is in the on position.
Ive never worked out how to test if the actual sensor works as they are a pain to get out without damaging them.

Some people put in temp gauge sensors like you say, ive never done it but ive heard of it and read of it in here.

 

[glenn property of pam]

the gauge and temp sensor has to be matched so choose a temp gauge then order a temp sensor to match it.
On my 80's 120hp I found a hole on the head that was about 1/2 deep and 1/4" diameter that was unthreaded. I just bought a 1/4 npt sensor then applied some heat transfer paste and screwed it in to the hole. Then I ran one wire to the console and landed that on the sense of the temp gauge. Jumped power of the gauge next to it and it works fine. You may have to make a bracket to hold the tip of the sensor against the cylinder head if you can not find a hole to use.

 

[emdsapmgr]

Your engine is not equipped by the factory to send any variable temp signal to a dash gauge. You will need to purchase a temp gauge and matching sensor as a kit. You will have to make a "Z" bracket for the sender. It will bolt to one of the heads and hold the tip of the sender flat to the face of the head. It will be sufficient to drive the temp gauge. Just be aware it only shows the temp of one head. Both heads cool independently, so the other head could overheat while temp gauge thinks everything is just fine.

 

[racerone]

A dealer will order you a kit.---Quick and easy and not much $$$