I can leave it running with the a/c on full blast for 30 min and it doesn't overheat...but once I hit the road it starts over heating after 10 min...both fans work...no leaks visible...took the thermostat off and ran it without it and it still overheats....maybe the water pump?...or a sensor?...,help please....

 

The fans work differently when the a/c is on versus when the a/c is off.

When the a/c in not on, the ECU looks at the ECTS (Engine Coolant Temperature Sensor) output for when it should turn on the fans, which is 203º F.

When the a/c is turned the ECU turns on the fans so that the refrigerant coming out of the a/c compressor gets cooled.

You may have a bad ECTS. Have someone with an OBD code reader check out what the engine coolant temperature is. Or do a resistance test on the ECTS as shown on page 204 of the service manual - link below.

http://boredmder.com/FSMs/Nissan/Maxima/2000.5/EC.pdf

 

Okay I will replace the ECTS...and go from there...also makes a ticking noise where water pump is located...