OK I just bought a 04 G35 Coupe about a month ago with 40000 miles on it. I thought I was getting a great deal when i bought it but now im not so sure. My problem is im in the military and the car has to sit for 2-3 days without ever running and today on my way home as i was driving i looked down at the guages and i notice the temp gauge is reading really uberly hot so as soon as i see it i pull over and kill the car, i pop the hood nothing is leaking. nothing is hot, i check the fluid and its full and even its not too hot, the resivoir is fine, so i start the car back up and it still reads hot but drops back to normal very fast so im like ok, i hop in drive a few miles and it does it again, but this time i check something else and dont pull over i drive a little ways and the car drops back to normal droping a peg on the temp gauge about ever 30 sec, i myself think it may be the sending unit going bad, but i need other opinions and would like to know if this would be waranty work, I need help fast as this is my only car at the moment and need it working right

I had this happen with my BMW once - you have a air bubble in the cooling system that's causing circulation issues. You need to bleed the system and get the air bubble out. Search google for some basic methods on how to do this. It's hot hard - I had to do it on someone's front lawn ("May I borrow your hose please") because the temps were not coming down for me.

exbmwdude2006 M35S

Also, and I know this is more obvious but make sure the belt to your water pump is ok. I'm not sure what kind of belt system that year G35 used but if the water pump belt breaks, it can overheat even in mild weather.

could also be sticking thermostat?

Thx problem is fixed now, I had air that kept getting into the system through a cracked cooling line off the back side of the motor.