somethign wierd is going on here , ever since my battery exploded and i had to replace it witha new battery , thewater tempreture reader is acting up.

at start it works fine

but after i start the car , the reading drops to 165ish fahrenhiet and stays just slighly above that area, before it used to go to the middle point of the guage

please let me know whats going on here? if anyone faced the same troubles?