Check sendor grounding
Only need a small hose clamp and length of wire. Use hose clamp to attach wire to sender connect other end to battery terminal bonded to ground.
See if that makes any differance
IF NOT
Get new sender and matching instrument. They must be a matched setup.
Hook up as described above on bench and get boiling water. Put water in cup and put in sender should indicate around 200. If you want to get really accurate and do your own calibration put in a thermometer. Add cold water for other temps and be sure to stir. Allow about 30 second for sendor to heat /cool before comparing to thermometer.
I have learned the hard way to ALWAYS check operation on bench before installation. Just because it is new seems to mean nothing in todays world.
Dan Bentler
