Temperature Gauge calibration

[wifegonnakillme]

I was testing my temperature gauge with a kettle of boiling water last night. The resting temperature seems is on the notch between 90 and 185F, or about 135. If i put it in cold water it will go down a bit. Hot or near boiling water will make the needle climb up to and past 230F...
Is it possible to calibrate the gauge or is it better left to the professionals? I think it is necessary since the car has not been on the road for a number of years (in the body shop now) and I want to have faith that i'm not going to overheat it on the first run out.
Thanks in advance,
kerry /ubbthreads/images/graemlins/canpatriot.GIF

BTW I'm looking for reasonably priced amp and fuel gauges too if anyone knows a source (for a driver)

 

[dklawson]

If it's a capillary (expansion bulb) type, leave it to the pros as the movement inside is a Bourdon Tube. If it's electric, you can calibrate the gauge yourself but it's tricky. Which do you have?

 

[Geo Hahn]

I think these gauges were fairly inaccurate when new, particularly at the extremes of their ranges. I suspect that is why they eventually dropped the numbers altogether.

I'd want to know where a 185 degree source reads on the gauge as that would be my 'normal', then consider what the gauge shows relative to that to spot overheating. The good news is that these gauges seem to be fairly accurate at normal operating temps.

 

[wifegonnakillme]

Its capillary...figured i wouldn't be able to do it myself - will take the advice above and try to figure out a normal spot and then watch for deviation -
thanks,
Kerry

 

[dklawson]

If you're going to try and make that type of calibration curve for your gauge, consider buying the Radio Shack (or other) infrared thermometer. Take a "dark" pan of boiling water and put the expansion bulb all the way in the bottom of it. Try to keep the bulb "off" the metal of the pan, only in the water. While the water is boiling make your first measurement with the IR thermometer (pointing it at the inner, wet surfaces of the pan). Turn off the heat and as the water cools make more measurements, comparing the gauge to your IR thermometer.

FWIW, I have a fairly new non-installed VDO capillary gauge and even it isn't precise when you get away from the 190-200 degree area. It's off by seven or more degrees when the water is "cold". A 30 to 40 year old Smiths/Jaeger instrument can be expected to have errors as Geo said.