cooling issues

[towncarblue]

i have a 2002 nissan pathfinder with 125k miles . my temp gauge keeps fluctuating when i am in street traffic. it goes from the middle to hot [ not enough to trigger the thermostat light ] . when i turn on the heater it goes right back to the middle. after i drive for about an hour and i shut off the car , i then put my key to the acc position and the temp gauge goes all the way up to hot. my reservoir tank is full .
i replaced my fan clutch and water pump last summer [2011]. what could be causing this problem ? how do i diagnose to get to the problem?

[Towncivilian]

Inspect your radiator cap following this TSB.

[towncarblue]

the radiator cap appears to be not functioning correctly . the rubber gasket is wider than the metal gromet

[Towncivilian]

Replace it with a new OEM radiator cap then.

[ttranter]

If replacing the radiator cap does not work. have the radiator flushed and cleaned at a radiator shop. I had a 2001 QX4 that had a similar problem. It turned out to be a partly clogged radiator even though I did change the fluid every two years.

[towncarblue]

i replaced the radiator cap.
the same problem still exists. drove the car out today and it kept getting hot , when i parked the car
i noticed that the upper radiator hose was very hot and my lower [longer , it connects to a thermostat] radiator hose was alot cooler.
could this mean that the thermostat is bad?

[Towncivilian]

Do you have access to an ODBII scan tool which will report coolant temperature? If so, you should be able to tell if the thermostat is opening properly (approximately 170F). If not, a new OEM thermostat is fairly cheap, I'd go ahead and replace it.

[CanuckQx4]

First thing I would do is flush the radiator with a garden hose, if you have the money why not spend $40 on a new oem thermostat with sweet new shiny metal housing, or if you have the time instead , remove and boil your thermostat and see if the valve opens to ensure its operating

If your rad is OEM a flush will definetely help you, and it costs $15 and an hour

[ttranter]

If you run the heater on high does the temp return to close to normal? If yes the Radiator is partly clogged

[towncarblue]

turned out to be the radiator. replaced it

[CanuckQx4]

could have flushed it, but kudos