I have a 1999 F-150 4.2 litre V-6 with 218,000 miles. If I turn on the AC it will overheat. It does this even while driving down the interstate at 70-75 mph. What could it be?
Saturday, September 8th, 2012 AT 3:18 PM
low coolant level
water pump impeller(common on fords)
blown head gasket which may be an issue with you as it sounds like you are driving it overheated
Saturday, September 8th, 2012 AT 3:23 PM
Coolant level is fine, am not driving it overheated as I monitor temp gauge and turn air conditioner off and pull over when it heats up also there isn't any water in the oil nor does it puff white smoke out of the exhaust when I crank it, why would the thermostat work when the a/c is off and malfunction when the A/C is on? How would I check a bad impeller on the water pump?
Saturday, September 8th, 2012 AT 7:13 PM
Thermostat can be partially open but I doubt it.
Water pump would have to be removed to verify impeller.
Leak down test will confirm head gasket