The engine may overheat at idle when the AC is on. A new, upgraded fan motor and resistor may be required to correct this concern.Google+
Car Problem Reports
Mercury Grand Marquis Engine May Overheat at Idle With AC On
Mercury Grand Marquis Problem
Average Mileage: 66,442 mi (23,000 mi - 110,000 mi)
Visitor, 2007 Mercury Grand Marquis, 110,000 mi
Replace engine cooling fan
Visitor, 2008 Mercury Grand Marquis, 55,000 mi
The engine may overheat at idle when the AC is on. A new, upgraded fan motor and resistor assembly should be put in.
Blowing hot air when idling or car was stationary. Drove it 15-20 miles....turned car off...started it up right away and the car made a strange sound and dumped contents of radiator....overheated. Dealership replaced fan and module $1000.