I know this has been hashed to death but I can't seem to find the threads. Water temp gauge is not working in my '80. Can I ground it at the lead for the temp sensor and get some type of reading or do I need to take it out and test it with a multi meter that way. Temp sending unit is new so I'm thinking that is not the problem. The wiring could be questionable but am not sure. Hopefully I'll have the car up and running once I get the trans back and put in about a week or so from now, but that's another story!

 

yes, if you ground the wire you should get full meter deflection. Measure the resistance on the sender with it cold and them hot and you should see a change.

 

Take the sensor and run a ground to the case and connect gauge wire. Heat up some water in the microwave or a hot plate. Measure the temp with a good thermometer and put the sensor end in the water. See if the gauge agrees.

 

You should be able to stick the sender in boiling water and read almost mid-way between the 200º and beginning of red-line (which is 250º) which should be like 220º...there's no easy way to test the 100 degree mark without some way to accurately measure the water temp.

 

Here's the procedure to diagnose temp gage problems:

Tests
A. Disconnect the green wire at the sending unit and turn on the ignition switch. The gauge hand should stay against the left side stop pin.

B.Ground the green wire disconnected from the sending unit. With the ignition switch still "ON," the gauge hand should swing across the dial to the right stop pin.

Corrective Measures
If the gauge hand does not stay to the left as in test "A", either the wire is grounded between the dash unit and the engine unit or the dash unit is defective.

Test further by disconnecting the dark green sending unit wire at the gauge. Turn on the ignition switch. If the gauge hand stays on the left hand stop pin, replace the disconnected wire. But, if the gauge hand still moves, replace the dash gauge.

If the gauge hand does not swing across the dial as in test "B", there is an open circuit in the wire between the sending unit and gauge, the gauge is defective, or current is not reaching the dash gauge.

Test further by grounding the sending unit terminal (dark green wire) of the dash gauge and turn "ON" the ignition switch. If the gauge hand now moves, replace the disconnected wire. If the gauge hand still does not move, connect a test lamp to a ground and to the power (pink wire) terminal of dash unit. If the lamp does not light, test the wire between the ignition switch and the dash unit by connecting a test lamp to the "Accessory" terminal at the ignition switch and to a ground. The test lamp should burn.

If the gauge hand operates correctly as in tests "A" and "B" but the gauge does not indicate temperature correctly, either the sending unit is defective or the dash gauge is out of calibration. Replace sending unit one of known accuracy. If gauge reading is still incorrect, replace dash unit.

If the gauge hand is at maximum at all times and test "A" and "B" indicate that the wiring and the dash unit are in condition, the sending unit is bad and needs replacement.

If the gauge hand will not move, the dash unit is bad, or incorrectly installed. Correct the installation or replace the gauge unit.

 

I'll jump on that in the morning when the Miller Lite wears off! The gauge has shown a couple of erratic readings on the low side. I've run the new engine only for about ten minutes total but no signs of overheating, but obviously I need to know the temp. Thanks!!

 

Thanks all!