Pantera DeTomaso Temperature Gauges

Over the years I have heard that the temperature gauges in Pantera’s were a bit off. And, I’ve heard that adding a 10 ohm resister in series with the temperature probe would make the gauge more accurate. In fact, at least one vendor offers a nifty plug and play setup to do just this. Our car came with the 230F gauge – which shows 160F as the centered point on the scale. With a 190F thermostat – the car always looks like it is running warm. And, when the car is actually hot – as in I set the radiator fan controller to come on at around 210 and off at 220F, well, it looks like the thing is really too hot, with the needle way over to the right. I was also aware that later cars came with 260F gauges. So, I set out to find a 260 on eBay. Sure enough, one showed up and found a new home. Naturally, I was curious how accurate it was. And, well, for that matter, how accurate the original was. Early on I tested the 230F gauge to see if the Echlin TS6628 temperature sensor would work. I set up this apparatus to see what I could learn – an aluminum container filled with water that I could heat with a heat gun, temperature sensor and temperature gauge in the water, two volt-ohm meters to see what the sensor’s resistance was, and the temperature gauge left in the dash, with the engine wires extended to the temperature sensor in the aluminum can. Oh, I used a screw driver to stir the water in the can.

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Figure 4 – 260F eBay Gauge Temperature vs Resistance Plot

This gauge is off by 34 degrees at an indicated 90F and around 10 at an indicated 230F. It is reading low, like the 230F gauge discussed above. But, the slope of its response curve is different: It almost looks like it would read correctly at around 250F, except the gauge reads lower again at 260F.

Note – when testing gauges I used rheostats to set the desired resistance (ohms) for a given temperature, based on the curve presented as Figure 1. I only had to do the hot-water bath test once – to check calibration of the sensor.

Which brings me to the real subject of this article – how to correct a gauge that is off.
I know just enough about electronics to generally not get the poop shocked out of me when doing wiring. Generally. First thing I did was draw a circuit diagram for the temperature gauge circuit, including some options for adding resistors to change the gauge response.

Original 260F Temperature Gauge