My gauge doesn't read properly. It doesn't reset to the correct temperature. It pegs on crank, then goes wherever the hell it feels like. But let's say it feels like going to 190, I can watch it raise up to past 260. And I know it's 60 degrees outside and I'm starting it first thing in the morning. The fact that the gauge still tracks makes me think that the sensor works, just the gauge doesn't.
Is there any way to test the gauge out of the car? I bought a used gauge from MDM, and I want to test it before I just toss it in the car and hope for the best.
F: Coolant Temperature Gage Test
- Disconnect the Coolant Temperature Sender connector and place the Ignition Switch in RUN.
- If the Coolant Temperature Gage reads cold, go to the next step.
- If the Coolant Temperature Gage does not read cold, check BLK (150) wire at terminal of Instrument Cluster Printed Circuit connector C2 for an open (this is the black wire coming off of the black connector for the PCB at terminal 9) and DK GRN (35) wire and terminal G1 of Ignition Switch connector C1 (this is the dark green wire coming off of the black ignition switch connector) for a short to ground. Repair/replace as necessary.
- Turn Ignition Switch to BULB TEST.
- If the Coolant Temperature Gage reads hot, go to the next step.
- If the Coolant Temperature Gage does not read hot, check DK GRN (35) wire for an open (see schematic) (you want to check it for an open between the ignition switch and the coolant temperature gauge. Not sure which location it runs to.). Replace Ignition Switch if wire is OK.
- Ground DK GRN wire at Coolant Temperature Sender Connector.
- If Coolant Temperature Gage reads hot, replace the Coolant Temperature Sender.
- If the Coolant Temperature Gage does not read hot, check DK GRN (35) wire for an open. Replace the Coolant Temperature Gage if wire is OK.
Coolant Temperature Gage
The Coolant Temperature Gage is also operatied by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Coolant Temperature Sender. This has 55 ohms resistance at 260* F (hot coolant) and its resistance increases at lower temperatures. Resistance is approximately 1400 ohms at 100* F. This causes the current flow through the sender and one coil to increase as the coolant temperature increases. This moves the pointer.
Also, this came out of my Helm manual for a 1987 Chevrolet Camaro. YMMV.
Just tested my temp gauge. There were three prongs that the thing mounted on. The top was power, left and right were grounds. Left was ground from the sensor, and the right was ground during cranking. If you hook up a 9v positive to the power, negative to ground, it should peg the gauge. If not, gage is bad. It might be bad under other circumstances, but it's 100% bad under that circumstance.