overheating on highway. completely lost

[rebelmp]

Hey all,

I've got an 03 eb 5.4. Truck started overheating on the highway.Put in new t-stat, water pump, fan clutch, and serpentine belt then took it in for a full system flush.

Runs perfect on regular roads. Once I'm on the highway, around 70 mph, she starts overheating. If I get off highway, she stays hot till I turn her off for hhalf an hour or so, then runs fine again.

Had the mechanics check. Head gasket is fine, and truck passes a compression test.

Doesn't need ac on to overheat, but that speeds the process up (doesn't overheat with ac on high on regular roads).

I'm completely lost at where to go from here. Any thoughts?

 

[bedrck46]

check your water level, could be air trapped in the system possible faulty CHT sensor

 

[sgtowing]

Clogged radiator perhaps?

Sent from my SCH-I535 using Tapatalk

 

[rebelmp]

Wter level is good. May be air, but Firestone said their machine makes sure to get all air out. Not sure how much I buy it though. Will look into the sensor.

As for the clogged radiator, if it were clogged, wouldn't I not be getting any coolant in the upper rad hose when the truck heated up?

 

[bedrck46]

when the engine heats up the T/Stat would open and water would flow from the block thru the upper hose to the Radiator So it would be possible that if the Rad were clogged the upper hose would feel full

 

[JUST4FUN]

Take the top plastic piece off thar covers the top of the rad and condenser look in between your looking for fuzz or dirt clean as needed

 

[stamp11127]

When you changed the water pump what was the condition of the block behind the pump? Clean, somewhat rusty or caked with rust?

If there was any rust present you may have a partially clogged radiator. It would be able to cool at low rpms but not have the capacity to cool at highway speeds.

Think of it as trying to cool the engine with just the heater core. It would be able to remove some of the heat but once you speed up then it can't handle the extra heat being put into the system.