about 3 days ago, my heat stop working, ithought my car isnt warm enough but after hours, it still doesnt spit out hot air. then today... my temperature gauge keep going up. it goes right under the "h". If i press on the gas pedal, most of the time, it goes up More!, but other times it ll drop down to the middle and go back up again.

i changed my coolent this summer, so i doubt its that.
someone told me i need more water in my radiator? how would i know i need more, how much do i fill up?

what else can cause these problems? are they related?

 

Thermostat maybe?.. if your car is overheating thats usually the first place to check.

 

Thermostat...go ahead and order it from your local Nissan dealership and change it...I remember it being under $20 for the part....

 

This exact same thing happened to me a couple of weeks ago, it was my thermostat, really easy to change, took about 20 minutes with haynes manual.

 

Thermostat change is covered in the FAQ now. It cant hurt to go ahead and change it. While your at it, completely flush the coolant system. You may have a blockage somewhere.

The Haynes manual covers coolant change/flush procedures.

 

Check the radiator to make sure coolant is filled up to the cap. If there is air in there, there is no heat and the engine would overheat, too. Also put more in the overflow bottle.

 

what size tools do i need to install the thermostat?

 

what0 tools/(sizes) do i need to install the thermostat?

 

There are three bolts holding the thermostat housing. I believe that they are 12 mm bolts. You also need to take off the hose clamp and and want to remove the horn and overflow bottle to give yourself some room to work. (Like others have previously said) Once you have the thermostat out it is an ideal time to flush your cooling system