[Tommy]

Gaz64 is right. For example, it has long been difficult to get a temp sending unit that works right for my 1963 Corvette. About 15 years ago I added a resistor to the wire from my sender to get more accurate resistance readings to the original gauge. ... But, I recently removed the stock instrument panel and replaced it with a custom panel with new Speed Hut gauges. The Speed Hut temp sender has a two-wire connection with one wire connected to the body of the sender that is supposed to be grounded to the block. The gauge itself has its own power and ground connections. I found that a poor ground between the sender and the block caused intermittant high temp readings. It may be uncommon, but it can happen.