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Temperature gage.

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Remy

Freshman Member
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I recently run my TR6 for a while, and when the temperature
gage was slighly above the middle point, I unplug the wire from the temperature sending unit and pointed the electronic
(laser beam) to the sender tip I got a reading of 168.9 degrees.(Farenheith). I understand that the middle point in the gage indicate approx 180 degrees. Is this a good and reliable test? which one is correct?
Hope to any of you that can shed some light to this.
Remy
 
Non-contact temperature gauges rely on a property of the measured surface called 'emissivity', which can be rather low for heavily oxidized aluminum (like your thermostat housing).

But given the uncertainties with the stock temp gauge, I'd say most of the error probably lies with it. For example, there is a device called a "voltage stabilizer" which, if it fails, can cause the temp and fuel gauges to read approx 1/4 scale too high (more if the alternator is charging the battery).

The stock gauges were also only approximate even when new, and can sometimes change over the years. One of the gauges from my Stag was so loose inside that just setting it on the bench would change it's calibration!

If you want to pursue this, I would suggest getting a contact-type thermometer (a "candy" thermometer will do). Remove the rad cap, run the engine until the thermostat opens (radiator gets hot), then stick the thermometer into the water. It's reading should be very close (within 5-10 degrees anyway) to the actual temperature at the gauge sending unit.

If you want to get closer than that, buy some purified water and measure it's temperature at boiling with the thermometer, and correct for barometric pressure. To really do it right, start with a lab grade thermometer, and calibrate it both at freezing and at boiling
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