Engine water temp gauge quit working...

I have an 86 Glastron/Conroy with a Mercruiser 170. Everything has been good this year, but this time when I got the boat in the water, I noticed the temp gauge was all the way down to the left and never moved. I checked to see if there was any power to the gauge, and to the best that I could tell today, there was. I have never had any trouble with the motor getting over 160 deg this year, and there aren't any leaks. I didn't have my manual with me, so I couldn't follow the wiring back to find out where the sending unit is. I will be doing that tomorrow. Does anybody have any experience with this that could possibly give me some more clues! Any help is greatly appreciated!

Re: Engine water temp gauge quit working...

Do you have 12v to the + terminal on the gauge? The - has a grounded black wire on it? Does the sender terminal have *some* resistance to ground? (50 -1000Ω but not 0 or infinity)

The sender will be near the water pump and/or thermostat housing. Look for a brass hex fitting with a plastic rod in it, and an 8-32 brass stud in the middle. There should be a wire on it the same color as at the gauge sender terminal.

If all looks good, with engine warm and key on, check for voltage to ground at sender, should not be 12 or 0, but somewhere in between. Same at gauge sender terminal.
e.g., if sender has 4 v to ground, gauge will have 8 v from + to sender terminal.

Re: Engine water temp gauge quit working...

Or alternitavely, turn on your ignition, pull the wire of the temperature sender near the thermostat housing and connect the wire to ground (negative terminal of battery), you temperature gauge should go to the top (Max temperature) of its scale. If it does then your sender is bad. If the gauge does not go to the top of the scale then you have a wiring problem (or blown fuse on the Positive supply to the gauge) or a broken gauge.

Gary