I changed out my timing belt water pump new antifreeze and still when I jump on the highway for about 40 to 50 minutes later, The temperature would go from normal to Cold the needle would basically drop. Im about to get my thermostat changed because I think it may be getting stuck on open but still would this happen because of an open thermostat? I had a maxima a while ago and at one time a drove it with out a thermostat and it drove fine. It may have took longer than usual to get to normal temperature but when it did it didnt get cold or hot after long driving.
What could this be a faulty temperature guage? When I slow down after higway speeds to city driving limits the temperature goes back to normal, never over heating.
Help... I searched the FSM and no Dice.

 

1. Verify u gauge from airflow with u personal temp sensor: fingertip

2. Read the for um: http://forums.maxima.org/showthread.php?t=377475

 

In my car the thermostat was stuck open and I had the same symptoms. It would run normal until I hit the highway and it was really cold. Then the car would start to run cold. When I shut off the heat it would return to normal, and then .....

You can check to see if the thermostat is stuck open by starting the car cold and looking through the radiator cap to see if there is movement in the coolant. If the t-stat is closed there should be no movement.

 

When you refilled it with coolant, did you open the bleed screw on top of the engine? Also, when refilling, did you have the heating lever all the way to the right (hot)?