2000 F150 4.2l V6 Overheating

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Apr 28, 2021
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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.
 

Bud_One

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So new pressure cap too? Does it push coolant into the recovery tank when the gauge shows hot? Are any of the hoses sucked flat during the overheating episodes?
 
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Try watching the OBDII temperature rather than the dash gauge. It has a pressurized reservoir system, so bleeding really isn't an issue.
 

Nick1994

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Aren’t those Ford gauges dummy gauges? Might need a cheap Bluetooth OBD2 reader to see live data on the actual temp
 
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Test the temperature sending unit and go from there. I had one where the gauge was displaying an overheating condition and it was actually within operating temperature.
 
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Temp gauge is not a dummy guage (oil presssue is on these). However, verifying with an OBD reader isn't a bad idea as the gauge may be "buffered" in a certain temp range.
 
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Seeing the temperature rise at higher highway speeds indicates a water flow issue. Don't overlook a colapsing lower radiator hose.
 
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The other suggestions are all more likely, but this an easy one to correct if it is the cause - ensure that you don't have too high a ratio of coolant to water. Coolant does not transfer heat nearly as well as water does.

I have only seen this once, but it does happen.
 

civhatch901

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So new pressure cap too? Does it push coolant into the recovery tank when the gauge shows hot? Are any of the hoses sucked flat during the overheating episodes?
No new pressure cap. Figure that is the easiest thing to replace and I didn't think of it! I looked at the engine bay during the overheating and never noticed the hoses being sucked flat but that I something I will double check along with replacing the pressure cap. Thanks for the suggestion.
 

civhatch901

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All great suggestions. Gave me several items to look at that are very easy.

I never thought to doubt the temperature gauge as it always moves to hot under the same conditions, (prolonged highway 75mph driving, very long uphills) but I will get an obd reader hooked up and double check.
 

civhatch901

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The other suggestions are all more likely, but this an easy one to correct if it is the cause - ensure that you don't have too high a ratio of coolant to water. Coolant does not transfer heat nearly as well as water does.

I have only seen this once, but it does happen.
Coolant was replaced last year along with the entire cooling system, I mixed it myself 50/50.
 

civhatch901

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You have a pic of the gauge when it overheats?
Under normal operating conditions it stays just below the half way mark. From there it begins to rise under the conditions described above (75mph highway cruising, long uphills) I never let it get past 3/4 of the way up. I don't have a picture. I will hook up an OBD reader as others suggested just to confirm actual coolant temp.
 
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No new pressure cap. Figure that is the easiest thing to replace and I didn't think of it! I looked at the engine bay during the overheating and never noticed the hoses being sucked flat but that I something I will double check along with replacing the pressure cap. Thanks for the suggestion.
The cap is not going to make it run hot. It's a myth. It raises the boiling point of the coolant by pressurizing the system.
 
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