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Why is my truck overheating?

Tiny
JERRYSHOWS
  • MEMBER
  • 1999 FORD F-150
  • 218,000 MILES
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

3 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Possible causes
clogged radiator
low coolant level
bad thermostat
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

Roy
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Saturday, September 8th, 2012 AT 3:23 PM
Tiny
JERRYSHOWS
  • MEMBER
  • 2 POSTS
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?
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Saturday, September 8th, 2012 AT 7:13 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
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

my gut is a bad radiator.

Roy
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Sunday, September 9th, 2012 AT 2:27 AM

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