Calibrating a factory temp gauge?.....

So with all of the temp issues our cars are known for, specifically the gauge reading wrong, I seem to remember someone here or on turboford that had the resistance readings of the different temp senders. I cannot find it through the search function. So my thinking is there should be a way to add a resistor inline for the gauge to have it read more normal based on what the ohms are for a known temp sender. Maybe an adjustable pot inline. I am just thinking of ways to have our gauges read normal with normal temps. Also, these temp senders were used by Ford for many years, but I tend to see three different colors. Red, Green , or Black topped senders. What's the differences? Any ideas?

The temp gauge sender is a NTC (negative temp coefficient) sender, meaning the resistance goes down as the temp goes up. The temp vs resistance transfer function is also not linear (it is a thermistor). If I remember right, sender resistance @ room temp is around 400 ohms, and around 22 to 25 ohms at 210 deg deg F. Putting a resistor in series will make the gauge read lower at a given temp. Many of the gauge problems in these cars is not caused by the senders or gauges, but by the archaic mechanical IVR. Solid state replacement IVRs are available on Ebay, or you can build your own for $5 worth of parts.

If you want to know the actual coolant temp install a real electric or mechanical temp gauge.