I have a 2003 frontier that is overheating. When I first start the temp gauge is in the normal position. If I stop and idle, (a/c on or off) the temp rises quite a bit above the normal range. No matter the speed after taking off temp is still above normal. If I then turn the heater on and blow or just let outside air flow through the heater coil it cools back to normal range in seconds. I have replaced the thermostat, even drilled a small hole to try and help, but no luck. Not sure if I have a plugged radiator or bad water pump. Any suggestions?

Replace the radiator. Phosphate scale may be plugging passages in the radiator. Refill with a 50/50 mixture of the recommended antifreeze and distilled water. Afterwards, properly purge all air from the system.

Replace the radiator. Phosphate scale may be plugging passages in the radiator. Refill with a 50/50 mixture of the recommended antifreeze and distilled water. Afterwards, properly purge all air from the system.

You were right. I had already ordered the radiator. Replacement fixed the problem.
Thanks

Good job.