Auxiliary temperature gauge suddenly stopped working properly

[willcarter]

Hi all,

Hoping for your insights on a new issue. My ‘57 came with an auxiliary temperature gauge installed because the temp gauge in the dash doesn’t work. (I’d like to fix that one day, but it’s been lower on my list of priorities because the auxiliary gauge was working fine). Because the auxiliary gauge came with the car, I don’t know what brand it is, how old it is, or how it was installed.

The auxiliary gauge had been working perfectly since I got the car, but for the past few days, it has developed a strange new behavior. Now, it will stay at 0 (zero) no matter how long I’ve been driving/no matter how hot the engine gets. The first attached picture shows the gauge after 30 minutes of driving, when the engine was clearly hot. I could smell that the engine was warmed up to operating temperature and the engine components were hot to the touch as usual once it’s fully up to temperature. The gauge stayed pegged at zero for the entire 30 minutes, whereas previously, it would, of course, start at zero but then gradually rise as the engine warmed up.

Here’s the twist, though: as soon as I shut off the engine, the gauge shoots up to the operating temperature all at once! (Today, that was 190 because it’s so dang hot today; a couple of days ago, it was the usual (for me) 180). No more than 10 seconds elapsed between it being at zero while the car was running and then swinging up to 180/190 after I shut the car off. I turned off the car; pulled the hood release; got out of the car; opened the hood; and went back to look at the gauge, which by then was up to 180/190.

I haven’t had any work done to the car since the issue has arisen and can’t really think of anything else that’s different that might be causing this odd behavior. The only two new possible factors I can think of are that (1) it’s been very hot here this week - could that be leading to a wire coming loose or causing electrical issues?; and (2) I *think* I’ve therefore had the air conditioning turned on on both occasions that this behavior occurred. I know I had it turned on today; I might have had it turned on the last time this happened, but I don’t remember. Could the A/C running cause some sort of interference or drain on the power to the auxiliary gauge that then goes away once I turn off the A/C and shut off the engine?

Any theories? And is there anything that I can check basically as a layperson to try to ascertain what might be going on (without access to a lift, any knowledge of electrical systems, and fairly little car knowledge overall)? It seems like too small of an issue to take it in to a shop just for this; but on the other hand, although I haven’t had overheating issues yet, I’m not comfortable having no working temp gauge at all.

Any thoughts are greatly appreciated!

[ICON 1956]

Will, I think you hit the nail on the head when you had the air on. It seems there is a electrical draw from the air conditioner that interferes with the electrical connection of the gauges. I know you are in the dark being you had no info on how the gauges were installed or what is the manufacture was. Check the connections. Has this been happening recently or when your using the AC...

[ward 57]

Will, I think you hit the nail on the head when you had the air on. It seems there is a electrical draw from the air conditioner that interferes with the electrical connection of the gauges. I know you are in the dark being you had no info on how the gauges were installed or what is the manufacture was. Check the connections. Has this been happening recently or when your using the AC...

Yup, connections. Possibly has been run to a constant hot connection instead of one that is switched.

[T-Bird Bob]

Hello Will,
This is a Stewart Warner Temp gauge.
Normally, the long sweep gauges (needle goes from 7 o'clock to 5 o'clock) are mechanical gauges, not electrical.
If it shows a temperature when you switch off the engine, it is most likely mechanical.

If it doesn't show a temp during driving, but does show one when stopped, means it has no contact with coolant when driving, but does so when stopped.

1) Check your coolant level.
2) Find your temp sender and put in a picture (I am just curious)

Good luck!

Bob