Oscillating Temp Gauge

[tex_n_ct]

Well, my search has been fruitless and I am currently stumped on one of the simplest systems on any vehicle.

For about 6 months I have been having an intermittent problem with the temp gauge swinging from the very low end of normal to the very high end of normal temps. It never goes out of the 'normal' range, but will oscillate between the 'L' of NORMAL to below the 'N' of NORMAL on a first gen temp gauge. The frequency is approximately 1 cycle per minute.

Have replaced thermostat twice, cleaned up all grounds that can be found, cleaned up connection to temp sender, verified no humongous voltage swings in electrical system (note: voltmeter has not been connected directly to sensor wiring when problem is occurring).

This happens most often at highway speeds and in all temperature ranges, from below freezing to over 100 degrees ambient. It does not happen all the time, but does appear to be increasing in frequency.

So. any off-the-wall guesses?

Thanks,
Ol' Bob

 

[Rick]

I've had the same thing happen on mine. Turned out to be a very slight leak between the plastic side tanks and the core of the radiator. Not even enough to drip on the ground, it was just seeping a bit, but that was enough that the system couldn't get up to pressure and that caused the swing of the gauge.

Go to Autozone, Pep Boys etc and have them do a pressure test. Check to see that it holds pressure.

 

[tex_n_ct]

Hmmmmm.....

Interesting. I will check the radiator and the cap - again.

I had a small leak about a year ago that was only large enough to discolor the radiator. Will clean it off and see if I have another micro leak. Hard to see on this X since it spends too much time flogging through the mesquite trees and creek bottoms.

Thanks much for the hint. Definitely something I hadn't thought of.