Heater Core coolant flow 97 F250 Powerstroke

If both hoses are hot, the problem could be the inside...could be a blend door actuator

You make sure reservoir is full if it's full after running 10 minutes or so check top and bottom radiator hoses and see if both are hot if only top one is hot may have a bad thermostat if both are hot it may have a heater control valve in heater line Goin into heater core

That sounds like a plugged heater core or heater hoses. At lower RPM there is not as much pressure from the water pump, so the coolant can't circulate through the heater core. Find the heater hoses (in and out) on the firewall. With the car running, engine warm to hot, squeeze the hoses - they should be hot and pretty tight. If they aren't, then something's probably blocking them. Then you'd just have to figure out if if it's the heater core that's blocked or the hoses. You can disconnect the hoses and blow compressed air in to the heater core. Probably a lot of crud buildup. It's messy but it can be done.

try some comma's?
my wild guess, is you are trying to fix a dead cab heater, right?
and if so, can be caused by 5 things wrong. total.
1 engine coolant not hot (180F or more)
2; fan dead.(cab heater fan)
3:or core , coolant path blocked. (seems you)
4; core exterior core blocked with leaves or pin needles. (sucked in)
5: optional core valve , stuck closed. (cable bad, etc)\



one pipe hot , means ,? core pipe 1 is hot, and other is dead cold?
this flow blockage , bingo !

if pipe 1 is 180F and other is 120f this is normal the heater is heating air in the cab and is dropping due to this heat exchange. (normal)
so why not do the 2 year full flush service now. (skipped i bet)
core hoses:
remove the 2 hoses on engine side, never core side (easy damage)
then back flush both hoses. with a garden hose.
if there is a valve there, test it and make sure it's opening... and free flowing.
and that both engine water ports are open too, from heater hose
to engine. (yes, they pack up too)

i wish you luck but is the temp staying in the usual place on the meter... could be as simple as a heater coil. or maybe the electronic control is not changing to flow water to heater core.. check engine light on?: turn heat on off on off on off to try to get it to change flow.. good luck

LOOKING AT HEATER CORE TOP HOSE COOLANT FLOW IN BACK OUT THROUGH THE BOTTOM HEATER CORE HOSE CHECK WATER PUMP BYPASS HOSE SEE IF IT GETS HOT.IF NOT COULD BE BLOCKAGE AT BYPASS HOSE FROM WATER PUMP OR WATER COULD BE FAULTY GETTING TOO WEAK PUMP COOLANT THROUGH SYSTEM.IF COOLANT GETTING HOT GOING TO HEATER CORE THE HEATER CORE AND COOLANT SYSTEM NEED FLUSHING OUT.

i don't know realy if there is a fuse (though i doubt it) but issues with heatting may be this will help.

If the carpet under the heater core is damp, or if antifreeze vapor or steam is coming through the vents, the heater core is leaking.
Remove it and install a new unit (most radiator shops will not repair a leaking heater core.
If the air coming out of the heater vents isn't hot, the problem could stem from any of the following causes:

• The thermostat is stuck open, previnting the engine coolant from warming enough to carry heat to the heater core. Replace the thermostat.
• There is a blockage in the system, Preventing the flow of coolant through heater core. Feel both heater hoses the firewall. They should be hot.if one of them is cold, there is an obstruction in one of the hoses or in the heater core,or the heater control valve is shut. Detach the hoses and back flush the heater core with a water hose. If the heater core is clear but circulation is impeded, remove the two hoses and flush them out with a water hose.
• If flushing fails to remove the blockage from the heater core, the coremust replaced.
  

If u have issues with heatting may be this will help.

1- If the carpet under the heater core is damp, or if antifreeze vapor or steam is coming through the vents, the heater core is leaking.Remove it and install a new unit (most radiator shops will not repair a leaking heater core.

1 - If the air coming out of the heater vents isn't hot, the problem could stem from any of the following causes:

• The thermostat is stuck open, previnting the engine coolant from warming enough to carry heat to the heater core. Replace the thermostat.
• There is a blockage in the system, Preventing the flow of coolant through heater core. Feel both heater hoses the firewall. They should be hot.if one of them is cold, there is an obstruction in one of the hoses or in the heater core,or the heater control valve is shut. Detach the hoses and back flush the heater core with a water hose. If the heater core is clear but circulation is impeded, remove the two hoses and flush them out with a water hose.
• If flushing fails to remove the blockage from the heater core, the coremust replaced.
  

No, you just won't have water flow through the heater core, Coolant flows through the engine through the lower radiator hose as the water pump sucks it out of the radiator and pushes it through the engine. It then flows out the top radiator hose when the thermostat opens. It then flows into the radiator to cool off.

Is your heater core leaking?

First make sure you have the radiator full of antifreeze also check overflow to make sure its at proper level . then let car warm up and feel hoses that go to firewall tword heater core and see if one of them are warm if so you have a blocked water control valve or its got a vacuum line off going to it .. Thanks Jerry holler if this is not it we will go from there.