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Heat

Discussion in '6.9L IH & 7.3L IDI Diesels' started by kbenz, Jan 19, 2021.

  1. renjaminfrankln

    renjaminfrankln Full Access Member

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    I would also raise the possibility of the cable looking like it is moving fine, but not making full travel due to a broken mount. That is if he did not pull the control unit out when checking it, and just pulled the glove box.

    Most likely either the damper arm itself is broken, or the cable isnt moving it all the way. Its a very simple system... if the heater core hoses are hot then it is extremely unlikely the core itself is so clogged as to effect cooling this much unless there was a much more obvious and severe problem w the cooling system.
     
  2. kbenz

    kbenz Full Access Member

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    ok. I have great air flow on ac but almost no flow on heat. Would that be nest or blend door possibly? Either way I need to pull the unit out correct?
     
  3. BR3

    BR3 Full Access Member

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    Not the whole unit, just the heater core cover. And maybe the heater core if you can't visually see the problem at that point
     
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  4. kbenz

    kbenz Full Access Member

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    cover and heater core out. No nests. Blend door seems to function fine. Nest in heat duct possibly?
     
  5. BR3

    BR3 Full Access Member

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    Well if you took the heater core all the way out, then you can see the whole portion of duct that would allow for good airflow in cooling but not in heating. The heater core case pulls air from the evaporator case, and if it blows good cold, there should not be an issue there.

    Can you post a pic of what your looking at?
     
  6. kbenz

    kbenz Full Access Member

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    I put it back together and it was blowing fine. Then it quit again. Selector switch maybe?
     
  7. BR3

    BR3 Full Access Member

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    Yea, try other vent selections, maybe the switch, resistor, or blower motor is having conditional issues
     
  8. kbenz

    kbenz Full Access Member

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    Coolant doesn’t seem to be circulating now. Radiator not hot. Mechanical temp gage only getting to 195 degrees though
     
  9. BR3

    BR3 Full Access Member

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    While thats certainly a problem, it should not cause low airflow issues from the vents
     
  10. kbenz

    kbenz Full Access Member

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    Yeah I know. Just aggravating. One thing after another
     
  11. gnathv

    gnathv Full Access Member

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    Is it defaulting to the defroster because of the vacuum?
     
  12. TNBrett

    TNBrett Full Access Member

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    So is the heater core getting hot when the coolant gets hot? If a mechanical temp gauge is reading 195, the heater core should be hot too. I’m other words, the thermostat doesn’t have to open for the heater to work. It sounds to me like you aren’t getting any coolant flow. How old is the water pump? Is there a ton of stop leak in the coolant? I’ve seen that crap actually wear the impeller in a water pump down to nothing. I’ve also seen plugs of it block coolant passages, and stop up heater cores. An engine full of coolant but without a functioning pump can actually run without severe overheating if not worked real hard. It does it through convection. As the coolant heats up in the engine it rises through the upper hose to the radiator, and cooler coolant is drawn up the lower hose to replace it. You would also probably feel some warmth in the heater hoses near the engine, but it probably wouldn’t circulate through the heater core. Just a wild hypothesis, this one seems like a bit of a mystery.


    Sent from my iPhone using Tapatalk
     
  13. snicklas

    snicklas 6.0 and Loving It!! Staff Member

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    Convection is how some engines are designed. The LoBoy that @chillman88 has doesn't have a water pump..... it just circulates as the temp of the water changes...... I believe IH called it a water siphon
     
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  14. kbenz

    kbenz Full Access Member

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    The heater hoses get extremely warm. Not the "I can't hold onto them any longer" hot
    No idea on water pump age,.
    Coolant has always looked good. When I took the plug out to put in the mech gage it looked good then too.
    upper radiator hose only gets warm from it radiating up there.
    radiator doesn't get hot either
     
  15. TNBrett

    TNBrett Full Access Member

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    I think the next step would be to disconnect the two heater hoses off of the heater core and connect them together with a piece of clear hose. Fire the truck up and verify that the coolant is circulating. If it is, hook the heater core back up,but keep the clear hose. This way you can verify that the heater core isn’t stopped up.

    If you don’t have any flow without the heater core in the loop, it’s time to pull the water pump.


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