The ohm difference between cold and hot vary depending upon the type used, about 100 ohms between the two seems about right, it might be more or less. They are a matched set like the gas gauge. Some gas gauges senders are 0-90 ohms, some are 78-10 ohms, you gotta know what you have or need.
You can calibrate both your temp gauge and gas gauge with the variable resistor. I hold my gauges to + or - 2 percent.
