2000 F150 4.6L overheats when towing

[Jaspernuts]

This has only happened twice. Once last year and once this year. Only happens when towing the boat on hot days with ac on going down highway. When it overheats I will pull over, wait 30 seconds and restart. Temp gauge has aready dropped down to 3/4 by then. Ac will blow warm when the temp gauge rises. The temp fluctuates when this happens instead of staying in the middle like normal. Coolant is 1 yr old, fan looks to be spinning normally. Any ideas?

[Jeremy airjer W]

If the coolant is full than I would blow out the radiator to start. Sand, cottonwood, debris will build up over time and block the cooling fins of the radiator limiting the airflow through it. Blowing from the engine side of the radiator with a blowgun will help clear that debris. We all have homemade blowgun tools just to do this. You may be surprised at the sandbox left behind after blowing it out.

The a/c blowing warm when this happens may be because the computer is shutting off the a/c to prevent further overheating. The condenser sits in front of the radiator and gives off a fair amount of heat.

The other possibility is the thermostat is not fully opening. On the cooler days this isn't a problem but when the system needs to operate at its maximum it can't keep up. We saw a simular symptom a couple of summers ago when it was really hot with the older Ford trucks. They where fine until highway speeds (not towing) and then they would overheat. A new t-stat was usually the fix.

[Jaspernuts]

I appreciate the fast response airjer. I thought about replacing the t-stat. Its a quick inexpensive guess. I will clean the radiator and replace the t-stat and well see what happens on the next hot day.

[Scott K]

Is it actually over heating? Is it steaming, blowing coolant out of the reservoir? It could just be a bad temp sensor.

[theoilman]

If it is cooling off in only 30 seconds I agree - it probably isn't actually overheating. Normally it would take at least 30 minutes to cool off, usually longer.

[Jaspernuts]

It is not blowing, steaming, or loosing any coolant. But with with ac blowing warm, Im just guessing that its running hot. Are u guys thinking a possible coolant temp sensor?

[Scott K]

Thats what I am thinking. If the pcm sees the coolant temp sensor is reading hot, it wont allow the ac to kick on and over heat the engine more.

[Whoaru99]

Usually though, if the coolant temp sensor for PCM/ECM is faulty, you get other drivability and or starting problems.

When the coolant temp sensor went out on my Camaro, I got a fault code and the thing ran poorly when it was warmed up.

In some cases (dunno about the Ford in question, but it is true for my Camaro) there are separate temp sensors for the gauge and for the PCM/ECM/computer.

My temp guage worked fine, but the scan tool showed the engine computer thought temperature was like -34F all the time, thus running way too rich when warmed up.

[BobT]

If you decide to change your thermostat yourself, there's something to be aware of. If the thermostat is located where it was on my 2001 5.4L you'll want to take steps to prevent antifreeze from spilling around the spark plug coil. Stuff a rag in there to absorb whatever fluid spills over. The coils are pretty sensitive to moisture. When I did mine some antifreeze got past the coil and down into the spark plug port causing electrical problems with my ignition. It wasn't real bad but it did cause my engine to run rough until I finally pulled the coil and pushed a paper towel in there to absorb what moisture there was from around the spark plug.