Engine Cooling problem
2001 Nissan Maxima 6 cyl Two Wheel Drive Automatic 160000 miles
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My maxima starts to overheat when my car is between 60-70 mph and the AC is on. The AC continues to blow cold air. If I turn the AC off and drop the mph under 50 then the car starts to cool down.

I've had both thermostats, fans, and radiator replaced and it's still happening. I've taken it to two different mechanics and neither one can find the problem.

As long I stay under 50 mph the car rides fine, but on the freeway is tough.

Let me know if you have ideas. Thanks in advance.

Make sure there isnt a bunch of road debris clogging up the a/c condenser in front of the radiator.You can wash it out with a hose and low water pressure or compressed air if you have access.Has it overheated before this started? has it been chemical tested for a blown head gasket?

It did over heat at the beginning of the year and that is when they replaced the fans and radiator. They've also replaced both thermostats and the radiator cap.

Someone had mentioned the water pump, but I don't know.

Two mechanics are stumped, so I don't know what to do.

Hi daversnyder,

Overheating only at high speed means the cooling is not efficient enough and the probable causes are

1. Clogged radiator.
2. Partially opened thermostat.
3. Clogged water passages.
4. Weak water pump.

I would suggest checking the water pump and water passages since radiator and thermostat had been replaced.