The Stovebolt Site Forums The Shop Area The Electrical Bay Water Temp Issue

I have a 1962 235 new rebuild with a new water temp sending unit (2 wire) Engine runs, green light for cold lights up, but does not go out when engine warms up. Wonder if it would show "hot" if necessary. How can I test it?

I posted on your other post. Check what temp it is supposed to come on at and use your gauge/ IR thermometer to check temp. That is how I double check my temp since I don’t have a light.

Chris

I am interested in the test method of this as well.

Anyone help John P and me? We have similar issue and are looking for a good troubleshooting tech for the temp sender and gauge/light.

Do you have access to an original wiring diagram? I believe I know how that light system is supposed to work, but it's been a long time since I've worked on one. If two wires are connected to the sensor, see if one of them turns the "cold" light on when grounded and the other turns on the "hot" light when it gets a ground. If so, I can suggest a way of testing the sensor.
Jerry

I will try that and report. Thanks Jerry.

Ok. Ground each lead and lights worked individually. So that confirms circuit is good and bulbs are good. (?). My specific issue is that i dont see the hot light when i turn the key. I believe the light is supposed to come on during a test. I suppose my ignition switch is now suspect?

Ok- - - - -some later model vehicles have a "self test" mode on the warning lights, but I'm not sure one of that vintage would have included that feature. Here's the problem with testing the "hot" section of the sensor- - - - -even boiling water will not get it hot enough to trigger the "hot" warning light. That's because "normal" coolant temps can get into the 250-degree range before the coolant starts to boil. That's because a pressure cap raises the boiling point 3 degrees for every pound of pressure and a 14 lb. cap is correct for your truck. That puts the "coolant boil" temp at 257 degrees. You'll need to use a heat gun or some other type of heat source and get the sensor up into the 250-degree range or so to see if the hot lead gets a ground. That will need to be done with the sensor removed from the engine so the sensor can be heated and the circuit checked with a powered test light or an ohm meter.

Edit: Sometimes the "hot" light self-tests while the ignition switch is in the "start" position. Check that out before swapping switches. I'm not really sure if any kind of dash light self test was used, however.
Jerry

Pretty sure I read the owners manual that all the lights check during the start position of key turn. I will check the sensor with some heat.

If you disconnect the energize lead at the starter solenoid temporarily, you can go to "start" at the ignition switch without actually making the engine spin over. Just make sure that lead doesn't get grounded- - - -tape off the ring terminal.

You can use cooking oil in a small saucepan to test the sensor- - - -use a meat thermometer or a candy thermometer to monitor the temp, which can go much higher than boiling water can. When you're done testing, toss in a few French fries- - - - -the oil is already hot!
Jerry

I can try that

Thanks to all for the suggestions. Been out of touch, but will try some of them and report back.