Originally Posted by ericnova72
Sender is just a thermistor(temperature variable resistor) inside it, resistance decreases as sender gets hotter. Could be it is the wrong value range to match your gauge, or you have a short to ground. If it reads cold with key on and engine not running and cold, but goes to hot too quickly when engine is started I would expect wrong range or faulty sender. If it goes to pegged hot as soon as power is turned on or engine is started, I would look for a dead short in sender to guage wire or guage wired wrong.
You could check it with a temporary test install of a mechanical gauge from the local Autozone, Napa, etc, or check the block and head castings temp with an infrared gun(laser thermometer)
That's what I suspect. Checked it with IR sensor, and found it to be in the 145 range while the gauge reads 240. But I'm fighting th' lack of education of my employer. And cannot convince him that just 'cause th' sender is new, and came with th' gauge, it can still be either bad, or wrong value.
This is the same guy who didn't want to spend the $30 for an oil pan gasket, to inspect the bottom end of an engine that he knew nothing about, proceeded to buy all kinds of high dollar stuff to go on it, then blamed me when it knocked like a Detroit Diesel outta oil, when it was first fired.
Found every bearing to be worn past the copper, broke rings, scored cylinders, worn out guides, burnt valves, 3 lobes on th' cam shot, lifters with wobbly rollers, etc. Engine was junk. But now he's too far into it to change the engine, and needed to re-build it. when I could have popped th' pan off an' found it to be worn out, and he could have bought a new one from GM for less money, and have a better warrenty. But he was afraid that it would be good, and he'd have to shell out a couple of buck fer a gasket.