View Full Version : Water Temperature Gauge

04-01-2003, 06:14 PM
Aloha All,

I've just started driving a '58 TR3A that I bought to replace another TR3A that I gave to my son (a great reason to upgrade to a better TR3A). The water temperature gauge in this car is an electric gauge that uses an electric sending unit. I've noticed this gauge seems to be constantly changing. I am assuming the sending unit and gauge is a from a TR4 or later TR series. The gauge is a Smith's and the face is marked with "C", "N" and "H". The car does not have a thermostat installed and I have observed that at highway speed the gauge reads around the "N", but at a stop and at idle it will rapidly drop down towards "C". Upon moving, the gauge will move to "N" in a matter of 5-10 seconds. I did have a 165 degree F thermostat that I tested before installing, and the gauge would initally gradually move to the "H" and them drop back to "N" (I think after the thermostat openned). The car has not boiled over and is not losing coolant. I have a 70% water/30% antifreeze mix with water wetter added as coolant.
I have used a instant read thermometer to get the temperature of the coolant in the radiator and it is about 170 degrees F when the gauge reads "N".

My question is, are electric water temperature gauge more sensative than the older capilary tube remote reading thermometer gauges? My other TR3A the water temperature gauge did not have such rapid changes in readings. Could the gauge and sending unit be miss matched? I don't like seeing the gauge at "H", but the car doesn't seem to be over heating.

Any and all advice will be greatly appreciated.

Safety Fast,

Gary Pope
04-01-2003, 06:57 PM

The electric temp gauge is one of the more reliable gauges and should not move rapidly at any temperature. Usually, the gauge would go towards hot while idling and go cooler while driving because of added air cooling.

It sounds like you have an electrical problem, probably not with the sender wire as it would go towards Hot when risistence is zero or grounded.

You may also need a voltage stabalizer which helps keep the needle regulated and smooth.

04-03-2003, 04:49 AM
Thanks for the input Gary. I checked out the wiring diagram for a TR4 and found the voltage stabilizer and see it seems to feed the wter temperature and fuel gauges, flashers and the wiper motor. I don't think the water temperature could be changing as fast as the gauge indicates, so the changes are probably generator output voltage related. My previous experience with my first TR3A was temperature increase at idle and decrease at speeds above 30 mph. I'll get a voltage stabilizer and try it out.

Safety Fast,