OK...Disclaimer first...This is not a nissan specific response...
I had the same thing happen on a honda accord 4-5 years ago. There was a crack in the pipe between the thermostat housing and the water pump, causing air in the cooling system. When I turned onto an on ramp, the temperature sensor was no longer immersed in water, it was surrounded by steam. The temp gauge went from rock steady normal to pegged in less than a second.
Moral of the story... If I had to guess, you have air in your cooling system, and in certain situations, the temp sensor is no longer covered by coolant. This will also allow uneven temps inside your motor and screw you pretty quick. I wouldn't drive it until I resolved the issue, or you may end up warping a head.
I had the same thing happen on a honda accord 4-5 years ago. There was a crack in the pipe between the thermostat housing and the water pump, causing air in the cooling system. When I turned onto an on ramp, the temperature sensor was no longer immersed in water, it was surrounded by steam. The temp gauge went from rock steady normal to pegged in less than a second.
Moral of the story... If I had to guess, you have air in your cooling system, and in certain situations, the temp sensor is no longer covered by coolant. This will also allow uneven temps inside your motor and screw you pretty quick. I wouldn't drive it until I resolved the issue, or you may end up warping a head.
