I have a 2002 Grand Cherokee that over heats only in stop and go traffic.

Asked by May 29, 2017 at 07:19 PM about the 2002 Jeep Grand Cherokee

Question type: Maintenance & Repair

I have a 2002 Grand Cherokee that over heats only in stop and go traffic.
Did extensive testing on the fan relay and motor and it checks okay. When
engine is cold and I turn on the AC the fans comes on and continues to run
while AC is on so I know the fan works. With the AC off and the engine hits
over heating temp the fan is supposed to come on but won't. It continues to
over heat until I turn the engine off to prevent destruction.  Why would the
fan turn on and off with the AC button but it refuses to come on when it
over heats? Also, once it hits the over heat temp the fan won't come on
when the AC is turned on (only when it is running at normal temp). Has a
new thermostat and radiator.

1 Answer

600

There's two things that the fans turns on for. One is the A/C and the other is high engine temperature. These are run by two separate controls. Apparently the temperature sensor on the engine is not calling for the fan to come on when it's hot. And you are wise to not overheat the engine, especially the 4.7 liter engine having aluminum heads and a cast iron block makes them sensitive to temperature extremes. On a related note, the 4.7 liter engine was known to have plastic water pump impellers that deteriorate with age, making the coolant circulate poorly. I hope this helps.

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