01 F150 getting hot

Joined
May 12, 2003
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Oklahoma
On my 01 F150 crew, 5.4l, 4x4, took 5 of us up a tall steep mountain. Outside temp was about 109, AC blowing and had it locked into 2 nd gear. Noticed temp gauge climbing up...and up....finally get to the top of the mountain, aimed the towards the wind, popped the hood and let it sit for a spell. Cracked the radiator cap just a little until it got close to spewing out. Temp dropped, when back down, all is good. On the way home, flat road, AC going, around 110 degrees, saw the temp guage go up, then dropped back down to the normal position. I've drained and replaced all the antifreeze about 5K miles ago. Fan works as it should. So, I replaced the thermostat and about half the antifreeze, even though it was all clean. When it started running hot that second time, I'm thinking the thermostat was maybe getting stuck or not working properly because I was driving on a flat road, engine running around 2K rpm, plenty of air moving through that radiator, then seeing the temperature guage drop. Anyway, was wondering what ya'll think. Don't really drive the truck a lot, it's not my daily driver, especially at these gas prices and 13 mpg, on a good day, downhill in a tornado. Also, being that the thermostat is factory original, just felt that was the right call. Truck has 113K on it.
 
Joined
Jan 1, 2003
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Daytona Beach
I'd say the thermostat is a good place to start. It might also be possible that there was a little bit of air in the system from the last drain and fill.
Before I replaced the thermostat, I'd get one of those testers that check for hydrocarbons in the antifreeze.
 
Joined
Dec 8, 2006
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Illinois
Make sure your radiator is clean. Had the same problem, and the radiator simply needed to be washed out. Dirt, bugs, cat tail fluff, cottonwood fluff... you name it, it came out.
 

Schmoe

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Hmmmm....we get lot's of that stuff and lot's of bugs. I'll try that too. Thanks. Sometimes it the simple solutions.
 
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Definitely check the thermostat, the radiator for debris, and the water pump. If it's the original water pump you might want to replace it. Overheating at speed with plenty of airflow usually indicates a coolant flow problem.
 

Nick1994

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Definitely check the thermostat, the radiator for debris, and the water pump. If it's the original water pump you might want to replace it. Overheating at speed with plenty of airflow usually indicates a coolant flow problem.
I agree with water pump.

But, radiators can be plugged from age too and have low flow. I'd replace it too.
 
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Might not hurt to buy a can of AC coil cleaner foaming spray from the local big box store and spray it. I’ve watched the before and after pressures when using it, works on HVAC, should work well on an auto.

edit - but yeah I’m leaning towards a sticking t-stat.
 

Schmoe

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Appreciate the replys. Drove it today, but it's not 108 thankfully. So far, everything is working and temp guage hasn't moved from it's normal cooling spot. Not seeing any tell-tale signs of common water pump failures. When I took the tstat off, shinned a flashlight down in the hole and used my boroscope, looked clean. Hoping it was a sticking thermostat. I'll get to flushing out the radiator coils this weekend..
 
Joined
May 4, 2017
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VA
The temperature gauge in most cars and trucks is controlled by the engine computer. The company's do that so that the gauge doesn't swing back and forth as the coolant temperature changes. So, if the gauge needle was going appreciably beyond the center position the cooling system is suspect. What's the cooling system's maintenance history?
 
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