I have an '06 350Z Grand Touring. A couple weeks ago, my "service engine soon" light came on. The car was throwing error code P0463 (Fuel level sensor circuit high input) which I fixed a few days later. However, a couple days after the light came on, I noticed that after 15-20 minutes of driving, my temperature gauge started creeping above the half way point and stops around 75%. Before, it sat a bit below 45-50% no matter the conditions. I haven't changed coolant or touched the cooling system at all. I also have been either running the heat or not having any A/C / heat on at all in the car, as its started to get cold here. This has re-occurred consistently since the light came on. If it happens while driving and I park, the temperature may stay around the 75% range for a few minutes before cooling back down. Sometimes, the temp doesn't start creeping up until I'm stuck at a long red light. The picture below is after a 15-20 minute drive home and sitting in the garage for a couple minutes.



Any ideas or feedback on what could be going on would be great. I'll provide more detail if needed.

 

I'd look at fans, and thermostat first.

 

How long has it been since you replaced the radiator cap? After 5-6 years they begin to fail- some more slowly than others and begin to lose pressure and cooling.

 

Been meaning to reply for a little while. I tried a few quick checks and nothing came of them, so I decided to take the car to a pro in my area. They did some extensive testing and the issue ended up being the thermostat. They pulled the old thermostat out and took a torch to it until the spring was glowing red and it wouldn't open. Not entirely sure what could have caused it other than pure age of the car.