’95 E320 temperature gauge reads full hot when engine cold.
 

If I pull the sensor wire the needle drops to full cold. The sensor wire has battery voltage and I put in a new sensor which shows about 330 ohms at 90F, same as the old one. After driving 10 to 20 minutes it will suddenly start acting normally. Any ideas what to check next?

Check out the grounding system.

Thought of that but all the other gauges are fine.

Probably why our Mercedes says the gas tank is full, when its actually empty. lol. $300 later / new sending unit, still on the fritz. :(

Good luck.

All the other gauges don't get their signal from the back of the car. If you installed a good, working level sensor then the wiring is about all that is left to check out. Something in that wiring system is touching something that it is not supposed to.