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Yet Another F150 Overheating

HELP! My 2000 F150 is overheating, When towing, it overheats much quicker, I stop and turn off engine, open the hood and the reservoir is full and hot, I tried slowly to unscrew cap and it was under pressure, so I closed it and wait 15 minutes and it cools back down and water in res goes back down! After the first overheat of the day, it oh’s much quicker. Things I’ve done, New radiator, flushed engine coolant, took out thermostat, checked for headgasket problems, I just don’t get it! With an enclosed system, how do you check water flow, the water pump is not leaking, but may be the impeller. Since the thermostat is out, can I remove the upper rad hose (cool start) and start it to see if I have flow/ I am out of money and can’t afford (no pun intended) throwing parts at it. Oh, I tried running it with the cap loose, it overheated but the temp gage showed normal! Thanks for any help.

I just checked my theory, I removed the upper radiator hose (no thermostat) and did a cool start, a gallon of water came out within 10 seconds as I quick shut it off, so that tells me the water pump is fine.

What motor?

How did you check for head gasket problem?

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Back in the 60’s a guy had bought a new Chrysler and used it to tow a camper. He showed me how he had brazed a larger tank on the back of the radiator to help with cooling. Do they have a heavy duty option for the radiator?

Another Ford story so maybe they aren’t as good as they used to be. We had our new 1954 Ford and drove it up to see the faces at Mt. Rushmore. When we got to the parking lot, most of the other cars, Chevys etc. had their hoods open to cool down, but our Ford didn’t need it. The temps stayed normal. I was only 6 at the time so I may have missed something but I was impressed anyway.

If your engine has a mechanical fan clutch it may be slipping and not pulling enough air.throigh the radiator.

If it overheats only when towing then do not tow anything until it is resolved. What engine and trans?
The fan may not be functioning as was mentioned plus is the fan shroud still installed?
Coolant should be correct mixture plus hoses must be firm.
One thing that is a red flag to me is you said the reservoir is full? It should not be so your radiator cap is failed or wrong pressure rating. When coolant has left the system and intoo the res you have an air pocket then the thermostat may not be getting coolant on it so it does not open thus no circulation. Not enough coolant to cool.
When you fill engine with coolant mix have it running and the heater going then add coolant until it is full and flowing check for correct thermostat as well… Check engine timing, correct spark plugs and good cables. Be sure exhaust system is not restricted and O2 sensor is not covered with grease or dirt. Air cleaner is clear clean and DO NOT run premium unless your book specifies. Do not tow more than the truck is rated for and brakes are not dragging. Tire pressure correct as well.
Be sure nothing is blocking the radiator grill.
Radiator cap first!

Pressure tested cylinders, spark plugs clean, no oil/coolant mix problems.TY

4.2 V6, sorry, I do not know the trans. I just picked up some G-05 coolant, it shows in manual to use it. I took thermostat out for testing. Is it possible for it to overheat because the coolant/water ratio is off? being the too much on water side?

How can I test it? The fan shroud is there (as someone asked me that)

Cool, literally.

Good ideas above. Here’s a couple other things to consider

  • removing the thermostat can actually cause an engine to overheat. It doesn’t seem possible, but part of the thermostat’s job is to adjust the proportion of coolant going to the engine vs the radiator. You may have too much coolant going to the radiator and not enough to the engine. This is especially true if your truck sports a bypass type thermostat.

  • If you have an automatic transmission, it may be overheating and causing the radiator to overheat too. The transmission is cooled by the radiator.

WOW, Nothing like the good olde days, ok I’ll put new thermostat in. How can I check if it’s the auto tranny overheating/

automatic with overdrive

The coolant will boil at around 220F without being pressurized, that is expected. What is the temperature in which it boils with the cap on?

It does sound like the fan clutch is not engaging. When the cooling system is at 220F or greater, raise the engine speed to 2000 RPMs and observe the radiator fan. The fan should roar like a propeller and blow your hat off, trucks have high volume fans to cool while towing.

TY, I will check that in the morning. More news, I live in Florida, so I never used the heater, I turned on heater, but no heat, just cool air. Can I flush a heater core with the 2 hoses attached to the engine ( i will have access as I put new thermostat in) can a clogged heater core make the engine overheat?

Please forgive my observation, and it is (My Opinion) It seems like the newer the vehicle, the wimpier it is! The only reason I went with a Ford F150 was because I had an earlier model ranger and it was a TANK, run straight water - NO PROBLEM, Bypass Heater Core - No Problem, it pulled my camper 100 miles - No Problem! Take out thermostat - No Problem! Now I feel I am walking on egg shells with this F150! It says in the manual for proper coolant DON.T USE THIS, OR THAT and the list goes on! I mean Cmon! Good grief! With the Ranger, I just turned the key and poof, I was gone! Now I have to pray to some sorta ford God and hop around the truck on one foot like the indians did to ward off evil spirits and hope it worked! lol

You say the vehicle overheats more when towing – could be your transmission is not detecting the strain/load on the engine and shifting to a lower ratio gear when needed. How many gears in your transmission? When you see the temp rising, manually down shift to raise the engine RPM thus taking the strain off the engine, and also increasing the water pump flow.

I’ve felt it downshifting, but it even overheats driving over 60 mph empty

Wrong, just because you used straight water in your Ranger does not mean that was correct.

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