Coolant only circulates at higher RPM

[Jonb10]

I want to start off by thanking everyone for the information shared on this forum. It has been extremely helpful in working through issues with my 2011 Explorer.

I’m currently dealing with a problem where the coolant only circulates when the engine is revved past approximately 2500 RPM. I recently replaced the engine (2011 for 2011 direct swap) due to the common water pump failure. The replacement engine has a new water pump and thermostat. I bled the air out of the system using the revving-and-holding method, followed by shutting the engine off, warming it up, and revving again.

Symptoms:


• The engine temperature climbs only when driving on the freeway at 60 mph with the engine at low revs (~1700 RPM). It’s fine during stop-and-go traffic.


• I get heat out of the heater when the engine is at higher RPMs, but the heat quickly dissipates as the engine revs decrease.


• There are no engine codes.


• The fans run constantly.


• The top radiator hose is hot, but the bottom hose remains cold, even when the engine is warm.

Any help or insights would be greatly appreciated!

Thanks,
Jon

 

[Turdle]

Is it possible a plug, or something similar in coolant passages, for shipping, was left installed,?

Faulty water pump?

How long run time for allowing lower hose to feel warm?

Does 2011 have radiator shutters?

 

[peterk9]

Welcome to the Forum Jon.
Faulty thermostat?

Peter

 

[FordFlintrock]

Sounds like it is air bound as these are finicky with the heater hose height and rear HVAC if equipped. I would do nothing until it is confirmed there are no air locks. This is pretty much a must have on current vehicles.

https://www.amazon.com/UView-550000...ref=pd_lpo_d_sccl_1/142-0233058-3263142?psc=1

 

[Jonb10]

Is it possible a plug, or something similar in coolant passages, for shipping, was left installed,?

Faulty water pump?

How long run time for allowing lower hose to feel warm?

Does 2011 have radiator shutters?

Yeah, I guess it could be plugged somewhere. I dread the thought of taking it all back apart.

I doubt the water pump is faulty. I went with the FoMoCo for that reason and it looked identical to the one I took out. The only thing that can fail on them is the bearing/seal, which it isn’t leaking coolant into the oil.

What are radiator shutters?

 

[Jonb10]

Sounds like it is air bound as these are finicky with the heater hose height and rear HVAC if equipped. I would do nothing until it is confirmed there are no air locks. This is pretty much a must have on current vehicles.

Amazon.com

Yes, it does have rear HVAC. I was getting heat through the heater so I assumed the air was bled out. I have heard they are finicky, but was told it will work out.

Thanks, I will try that versus tearing into it.

 

[GerryEX]

Yes, it does have rear HVAC. I was getting heat through the heater so I assumed the air was bled out. I have heard they are finicky, but was told it will work out.

Thanks, I will try that versus tearing into it.

Hope it is just air inbound. Update us

 

[Jonb10]

Hope it is just air inbound. Update us

Will do

 

[Jonb10]

Sounds like it is air bound as these are finicky with the heater hose height and rear HVAC if equipped. I would do nothing until it is confirmed there are no air locks. This is pretty much a must have on current vehicles.

Amazon.com

Update: Vacuum filling completely resolved all the coolant issues. You were absolutely right—removing air from the system of rear HVAC equipped Explorers is nearly impossible without vacuum filling. Thanks for everyone’s help!