My 03 350z is overheating. Oil is fine. No smoke out the back. Fans work. Just replaced the radiator and the thermostat. No leaks. I have notice that its not drink from the reservoir. Any ideas what it might be?

 

Best case scenario, you have large air-pockets in the system or a faulty temp sensor. Read up on how to bleed air out of the cooling system (There's even some YT vids on this). Are you getting heat from the AC system at idle? If not, then you're not done bleeding air after the radiator and thermostat replacement. Flushing or replacing coolant on 350Zs is a more involved process compared to the average vehicle out there. Otherwise, you may have a compromised head gasket (not fully blown, but small leak), I doubt this is the case since you just replaced the radiator/thermostat, this is a classic symptom of not burping/bleeding out all the air.
Cheers!
-Icer