340 overheating problem

It seems like there's been a rash of threads that I've been reading lately about temperature gauges that aren't accurate. I know that I've got a problem with my own. My factory gauge reads hot but I'm running a Mr. Gasket radiator cap that has a built in thermometer and it reads 180'. I used a portable infrared thermometer to check the engine temp and it agrees with the radiator cap so my interior gauge is off.

New parts store temp sending units for OEM guages have the wrong ohm resistance.

You need to add some resistors to adjust the unit correctly.