No where near the magnitude of effort or precision you took, but some time ago I compared the coolant temperature in the header tank (thermocouple immersed in the coolant) with the reading on the gauge and found the gauge read 5-10 degrees C higher than the header tank. I have no idea what the actual temperature difference is between the location of the temperature sender and the tank.
Cheers,
Rod
John,
Similar, but different. The dot on the speed indicates where you put the needle when installing it on the shaft, to properly pre-load the return spring. The marks on the small gauges are used when doing electrical calibration on the gauges. A power supply and a series of precision resistors are used to simulate an ideal sender. Specific resistance values should drive the gauge to specific positions, and the two adjusters on the back of the gauge are used to calibrate the gauge so it reads correctly at those resistance values. The dots indicate where the gauge should be for those calibration resistance values. This is done using a test box Smith’s sold:
Regards,
Ray L.
Ray,
Nice photo showing the Smiths Tester in use. One question: Have you taken the time to measure each RS resistor within the Smiths unit? I have five (5) Smiths units, all manufactured in the 1960’s and all have one or more resistors that are way out of spec. You may wish to calibrate the Test Set to insure accuracy for gauge needle values.
Just my 2 cents…
Happy Trails,
Dick
I don’t have, and have never even seen in-person, one of those testers. Years ago, I saw the calibration resistor values, but don’t recall exactly what they were. For the “Bimetal 10V” gauges used on the E-Type (except for Volt/Amp gauges) retty sure the center one is 70 ohms. IIRC, the lower is 270 ohms, the upper is 11 ohms, but can’t guarantee that. In the absence of a reliable source, a survey of a significant number of known good temp sensors could be used to verify the correct values, as all such gauges use the same movement.
