2000 F150 4.2l V6 Overheating

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Yes. To raise the boiling point. If there is a bad cap, it boils at lower temp - 212. Apparently you don’t know what happens if radiator boils over.
 
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Sure do. If the coolant has not boiled which it didn't, the cap itself is not going to raise the temperature gauge as indicated by the OP.
 
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I am not a mechanic but like to tinker. Bought this truck 3 years ago, only put 5k miles during this time.

Truck overheats on long highway drives or long up hills when driving at 70-75MPH. As I see the temperature gauge start to creep up I slow down and can control it that way but it is annoying and I am trying to see if I can get it fixed. Can idle or city drive all day long with no overheating issues at all. If I turn on the heat, it does not feel like it is as hot as it should be and has no effect on the truck's operating temperature, I am not sure if that is my mind playing tricks on me though. Besides overheating issue, truck drives great.

No check engine lights. No smoke out the tail pipe. No oil burning and no missing coolant in the last 5k miles. Oil looks normal, not milky.

Last year I overhauled the cooling system completely with OEM parts- radiator, water pump, thermostat, fan clutch, and of course fresh coolant. No change to symptoms. As far as I know, there is no way to bleed the coolant system beyond parking the truck uphill and letting it run for a while.

I am thinking this might be a small headgasket leak. I could do a leak down test but have not done that yet. Open to feedback and ideas/things to check.

You have already gone after the usual suspects. I have seen a lot of threads on the 4.2 overheating on the F150 forums, and usually it is traced back to the radiator or fan clutch. I did see one where the guy traced it back to a small headgasket leak, but that seems to be very uncommon.

What about the AC condenser? Any chance it is plugged and restricting airflow to the radiator?
 
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You have already gone after the usual suspects. I have seen a lot of threads on the 4.2 overheating on the F150 forums, and usually it is traced back to the radiator or fan clutch. I did see one where the guy traced it back to a small headgasket leak, but that seems to be very uncommon.

What about the AC condenser? Any chance it is plugged and restricting airflow to the radiator?
overheating on the highway shouldnt be a fan issue at highway speeds?
Fan issue would be more an idle or stop and go traffic overheat?
I'd suspect crudded up radiator inside and out maybe. Just cant move the heat out of the fluid efficiently..
because there is a considerable amount of heat to move to the air when you are going uphill.

Anyway you could get it good and hot then check the radiator in various places with an ir gun?
or how would you diag a radiator?
New radiators are around 150 on rockauto.
 
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Wow. A myth?? Put a gutted cap on your radiator and report back on the mythical results.
A cap does not effect the temp. Pressurizing a cooling system allows it to run above the boiling temp.

Without a pressure cap coolant will boil around 212F as adding coolant to water will raise the boiling point slightly.

Below the boiling point the coolant will be the same temp if it's pressurized or not.
 
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Solid points already mentioned, especially limits in air and or coolant flow. A sluggish thermostat will do this if it’s not opening all the way. If everything else looks clean, nice and tight, I’d check there. Have absolutely seen this before from a sluggish t-stat.
 
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A cap does not effect the temp. Pressurizing a cooling system allows it to run above the boiling temp.

Without a pressure cap coolant will boil around 212F as adding coolant to water will raise the boiling point slightly.

Below the boiling point the coolant will be the same temp if it's pressurized or not.
Theory is great and I agree with your analogy but in practical use a bad cap can cause overheating. For ****s and giggles try it on your own vehicle. Loosen the cap a notch and take off down the highway. You’ll be on the side of the road with the temp needle buried way past HOT.
 
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Theory is great and I agree with your analogy but in practical use a bad cap can cause overheating. For ****s and giggles try it on your own vehicle. Loosen the cap a notch and take off down the highway. You’ll be on the side of the road with the temp needle buried way past HOT.
It's going to get hot because all the water boiled out.
 
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It's going to get hot because all the water boiled out.
So a bad cap can cause overheating. Yes? No? A quart less in the radiator and in the recovery jug at highway speeds can cause an eventual overheating issue. Maybe a leak isn’t detected on the ground but too hot is too hot. I’m not sure what this discussion has evolved in to………?
 

civhatch901

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Apr 28, 2021
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You have already gone after the usual suspects. I have seen a lot of threads on the 4.2 overheating on the F150 forums, and usually it is traced back to the radiator or fan clutch. I did see one where the guy traced it back to a small headgasket leak, but that seems to be very uncommon.

What about the AC condenser? Any chance it is plugged and restricting airflow to the radiator?
I checked the AC condenser when replacing the radiator, it is clean and lets air thru just fine.
 

civhatch901

Thread starter
Joined
Apr 28, 2021
Messages
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overheating on the highway shouldnt be a fan issue at highway speeds?
Fan issue would be more an idle or stop and go traffic overheat?
I'd suspect crudded up radiator inside and out maybe. Just cant move the heat out of the fluid efficiently..
because there is a considerable amount of heat to move to the air when you are going uphill.

Anyway you could get it good and hot then check the radiator in various places with an ir gun?
or how would you diag a radiator?
New radiators are around 150 on rockauto.
Thanks for the feedback. As stated on the opening post, I already replaced the radiator and it made no difference to the symptoms.
 
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