The Stovebolt Site Forums The Shop Area Engine Shop Erratic temp indicator

I don’t know if this question would be better in the general or electric forum, but here goes. I have finally got the engine temp gauge to work, but I think it is reading incorrectly. At idle with the engine warm, it reads about in the middle of the gauge ( does the middle mark correspond to 180F?); as I build up speed and RPM the gauge climbs up to the top right away. As soon as the RPM drops, the gauge goes back to around the middle. It seems to be following the AMP gauge as both needles seem to move together. I have no issues with boil over, so I do not think it is actually getting that hot. Has anyone seen this before? Is it an issue with my voltage regulator maybe? I have not been able yet to monitor the voltage while driving so I do not know what is happening there. I finished a complete rewire about 8 months ago, and replaced the temp sender. When I was troubleshooting the inop temp gauge, I tried swapping out with a gauge from a 59 pickup, but that did nothing (and I cannot recall off hand if the 59 or the original gauge is back installed).

Thanks, Lee.

This is probably a stretch but in that swapping and switching senders you didn't somehow use an oil pressure sender for your temperature sender, did you? Sorry but I use mechanical gauges and don't really recall if the two could be swapped. However it sounds like your temp gauge is mimicking your oil pressure gauge to me. Turn your headlights on at idle. If your temp gauge drops, that tells us it is registering a drop in amps. If nothing happens, increase idle just a bit...maybe 500 or so rpm. If your temp gauge goes up just a bit, then it sounds to me like your temp gauge is somehow trying to give you oil pressure info.

Well, you people are going to think I've just dropped off the last branch in the tree and landed on my head. It just dawned on me I should have been asking "you didn't somehow connect your temp gauge wiring to your oil pressure sender, did you?" Sorry...the heat and humidity may have my brain tubes clogged.

Test with ignition on so gauge has power. Disconnect the sender wire and the gauge should read full hot. Ground the sender wire and the gauge should read full cold.

My oil pressure gauge is direct reading, and my temp gauge is electric, so I cannot switch the two. And with the lead disconnected, it reads full cold; with the lead grounded, it reads full hot. It seems to be following the amp gauge as it goes up (to full hot) when the amp gauge reads a good charge. And then drops to ‘normal’ when I am at idle and the amp gauge shows a dishcharge. I’ll do some more tests with the lights and voltmeter and see what I get.

Lee.