2001 nissan altama

temp gauge moves from normal position down the faster i drive,sometimes bouncing, any ideas?

Altima, with an “i.”

Check the level of coolant in the radiator (only when it’s cold). Make sure the radiator is full and the overflow reservoir has coolant to the correct level.

You may need a new thermostat. If your thermostat is stuck open, it will make the engine run too cool. This is bad for the engine and for your fuel mileage.

Or the engine temperature sensor might be bad, but I’m thinking thermostat. When the gauge goes down, turn on the heat. If you don’t get any, or not much, it’s the thermostat, assuming the coolant level is correct.

Your engine runs very well and the radiator is working great.