change water pump on a 1997 nissan pickup 2.4 temp coolant gauge bounce up and down from time to time any idea.

Did you change the thermostat and radiator cap? Also would have been a great time to change the coolant.

Sounds like air trapped in the system…Can be very difficult to bleed out in some cars…

seeing as how it is a 1997 u may need a t-stat and radiator cap as well but if it wasnt doing this before the water pump change you have air trapped in the system.