Adding a temperature gauge

[Prof T]

I have a 2016 Crestliner with a 90 Merc Fourstroke. I’d like to add a temperature gauge. The motor has a sending unit mounted near the thermostat that I believe tells it when to go into “safe mode” if it overheats.

 

Is that same sensor used for a traditional dash temp gauge? Is wiring already in place in the harness? I’ve looked around the internet and can’t find any information or schematics.

[LongLine]

You may want to ask on Iboats.com.

 

[Prof T]

Updated:

 

Mercury keeps their shop/repair manuals pretty well hidden on the web so I went off and purchased one. I plan to have the motor a long time and spent a career as an Industrial Arts teacher, so I like to do as much of my own repair work as possible.

 

The sender is mounted right by the thermostat and has two wires: tan/black and black/orange. The black/orange leads to a common ground for all of the sensor wires (ECM PIN 42). You can test the sensor by disconnecting its plug and checking with an ohm meter between the two wires.

32 degrees - resistance should be very high (32.6 k ohms)

 

77 degrees - room temperature (10 k ohms)

 

122 degrees - area where my last motor liked to run in cold water  - (3.6 k ohms)

 

212 degrees -OVERHEAT - 678 ohms

 

Sensor is very much like an automotive sensor, a wet probe into the water jacket.

 

It appears to me that I can use that probe and wiring to a traditional gauge like I wanted to. Shrink wrap comes off today, I’ll keep the wrench heads out there posted.