I had my radiator replaced because it was leaking. Drove my car home to just return it to the mechanic cause every time I pressed on the gas the temperature gauge jumped to cold. Mechanic replaced the water sensor, left the shop no more than 2 miles up the rode drove the car back to the mechanic because gauge now reading hot. Can someone please help I don't think this mechanic knows what he is doing.

Sounds like wire is loose on radiator sensor

Did the mechanic bleed the air out of the cooling system after replacing the radiator? What did he do when you brought it back the first time when the gauge was dropping to cold?

Your temperature gauge is bad, need to replace the cluster.