When you first turn your heater on it will circulate the cooler water in the heater core through the engine. This might make the temp gauge drop for a very short period but not abnormally low. Probably the sending unit..
> To Grandpa Joe: When you say the sending
> unit, what do you mean and is it a problem?
> I know overheating is a problem, but
> underheating? Could it be a faulty guage?
Jeff, if the guage stays in that position i would suspect the thermostst is stuck open. be sure if you need to replace it that you use genuine Nissan parts, there is a difference... the water passage in the Nissan part is bigger than others. you really need the flow and these off-brands are a restriction.