OK, here's the deal – my friend has a 2000 F150 it has the 4.6 L V8 and is overheating. Everything except the radiator has been replaced. New water pump, new thermostat, new fluids, New hoses, and the engine block has been flushed. For some reason, it continues to overheat. Coolant flow is uninhibited. He even took it to the local dealership, who simply suggested using Ford parts rather than aftermarket stuff - like a Ford thermostat. I just can't see that that's an issue.

He had a compression test done and has consistent 175 psi on all 8 cylinders.

It runs hot, not warm. Gurgling inside the radiator and even shutting off completely.

Since the coolant is flowing ok, I can't imagine that the radiator needs to be replaced. No leaks, by the way.

Thoughts?

Thanks,
William

 

Have some question, need some answers.
How long does it take from a cold start and under what conditions does it overheat?
What does the dash gage do?
Is the thermostat in place backwards?
Is the reservoir pressure cap known to be good?
Are you sure all air is purged out?
Has a Scanner been used to verify the live temperature reading?
Some questions may be obvious to you but not to me, from here since I only have your word to go on to try and help.
Good luck.

 

Thanks so much - I'll text your questions to my pal and get some answers.

Be back shortly.

 

Here's my friend's response: I like it where we offended him about the thermostat. Haha!!!

"Only gets hot running down the road. At ambient air of 85, takes 30 min to start climbing, with trailer in tow, 15 min. Dash gage slowly climbs towards red. Will cool itself at idle after 10 min. No, I'm not an idiot, the thermostat is not upside down. I haven't put a scanner on it for the temp, but have used an in fared heat gun and shot 265F coming out of the manifold to the heater core. Reservoir cap replaced 6 months ago."

So...what do you think? He didn't answer the question about an air pocket, but based on our conversations and how the water flows properly, I don't think that's it.

Thanks for the help and replies!

 

Well ok. I got enough from his reply.
Based on the extra info that was very important, I feel the radiator is partially restricted.
It now does not have enough cooling system capacity to meet the demands of towing at the lower road speeds where less air is flowing through the core..
Sorry you went through all the other work and expense.
Iv'e seen this before.
When the temp. gets high enough, the cylinder head sensor will send the computer into limp mode to protect the motor.
Then the power goes way down because all the cylinders are not in play.
The computer cuts off fuel injection on a round table basis to limit the temperature by just allowing the cylinders to pump air through for cooling as well as not producing any combustion heat.
Good luck.

 

Have your friend use his heat gun to see if the radiator temps are cooler at the bottom than the top when over heating.

I'm not sure how your friend has determined that the coolant flows properly, but the lower radiator hose may be collapsing when running down the road but not at idle. Ditto for the radiator flow when running down the road versus idleing.


What are his heat gun reading of different areas of the radiator core and tanks.

 

You can't use a heat gun out on the road.
At idle, apparently the signs of over heating are not there.
Do not over rely on a heat gun.
Your being stumped because of it.
A Scanner looking at live temperature readings on the road tells the story.
Coolant must take heat away fast enough, drop the temperature at the radiator and return back to the motor.
System pressure raises the boiling point of the coolant so it is able to run up near the 195 to 200 degree point with a large margin left.
265 is about the point the motor it taken into limp mode to save it for you from mechanical damage..
You cannot just pass these things off.

Good luck.

 

in addition to the internal radiator, don't forget about the outside of the radiator.. fins bent, oil / crud buildup , leaves / trash between the radiator and air cond coil.

 

I really appreciate all the comments. I agree that an infrared heat gun won't be real accurate. It's just all he had at the time. It at least told us it was hot, as if the other signs weren't enough.

I made the assessment that flow was unrestricted, probably incorrectly, based on the fact that I understood from a previous conversation that he didn't have any kinks, air, etc. and that it would cool on its own under idle, without movement and air flow.

Since my original post, he told me that he has found another rad online. It's all that's left to replace. Haha! If that doesn't fix it, I'm definitely stumped. Just wanted to help him figure it out before he dropped more coin.

 

Pay some attention to the fan clutch.
It normally will cycle following the thermostat open and closing time at idle.
To see this, use a timing light connected to any cylinder.
Shine it on the blades.
Note the visual in sync/ out of sync that should occur as it's speed changes with temperature sensing.
Good luck.

 

From what you've described I'd guess it's either a restricted radiator or the transmission is overheating and transferring that heat to the engine coolant.

 

True. I can't use the heat gun on the road. But if it gets up to 250* plus I can pull over, pop the hood and scan the radiator with the heat gun (and tell if there are portions of the radiator core plugged internally with crud and impeding coolant flow, reducing the radiator's cooling capacity) before the temp returns to normal..