Heat not working

Discussion in 'Engine Performance + Maintenance' started by scott_williams2, Nov 9, 2019.

Car Parts
  1. scott_williams2

    scott_williams2 OBS Enthusiast

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    I have a 97 k1500 with a 350 vortec. So recently it’s gotten cold and I wanted my heater but it wasn’t workin I just picked this truck up a month ago. The previous owner had installed a valve for whatever reason and it closed on the heater core inlet hose and I opened the valve and coolant went everywhere leaking out the valve so I changed this hose let the truck get completely warm and turned the heat on. It blew hotter on hot than it did on cold but still not enough to be considered heat. I don’t think the heater core is bad Bc it doesn’t leak any on my floorboard. Any suggestions???
     
  2. TechNova

    TechNova I'm Awesome

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    I had to back flush my core a few times last year and again yesterday. I also pulled one block drain, the other has the knock sensor, I didn't know if I could get it out. There was a lot of sediment in the core that came from the bottom of the block.
    Also check the actuators under the dash. One of them controls a flapper for hot/cold.
     
  3. Schurkey

    Schurkey I'm Awesome

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    Engine off, and "cold".
    1. Verify that the radiator is "full", and some extra coolant in the overflow bottle. Leave the rad cap OFF, start engine.
    2. Verify that the engine gets to proper operating temperature. Thermostat opens at 190-ish degrees F. You may lose some coolant as the engine warms up and the coolant expands.
    3. Verify that the water pump is moving coolant. You should be able to see coolant movement when you look in the filler neck of the rad. Reinstall rad cap. Add coolant to the overflow bottle as needed to make up the amount lost.
    4. Verify that BOTH heater hoses get H-O-T. Most folks can't hold on to them; but if you've got severe calluses or nerve damage, you may be able to.
    5. Does the vehicle still have the original restricted fitting for the heater core supply hose? Probably a "quick-connect" fitting at the intake manifold that's restricted internally. Lack of a restriction is hard on the heater core, and can cause leaks.

    If the heater hoses are BOTH hotter than you can stand, the problem is in the interior--probably a failed actuator, but it could be the dash control. Vehicles without A/C may have cable controls instead of actuators--I've never seen that, but I think the service manual describes 'em. Consult service manual for tips on diagnosing the control panel and actuators/air doors.
     
  4. evilunclegrimace

    evilunclegrimace Does not always play well with others

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    My '92 had enough casting sand left in the block that it would not heat up correctly. I ended up pulling the block out, knocking out the core plugs and power washing the cooling jackets out. Both it and my '98 had enough leaves in the heater box to obstruct about 1/2 of the heater core. A blow gun and a vacuum hose helped with the air flow.
     
  5. scott_williams2

    scott_williams2 OBS Enthusiast

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    Ok so after some process of elimination I’m almost positive it’s the blend door actuator. I took the glove box out and the knob is only turning halfway to the heat mark. Can anyone give me advice on how to change it Bc it looks hard and I can’t figure out how to take the ashtray out without breaking plastic lol
     
  6. east302

    east302 I'm Awesome

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    No guarantees that this is how it is removed, but the ashtray has four tabs on it. If you pull the square head pins just halfway out, it looks like it may release it from the dash.

    If it breaks, you didn’t hear this from me, lol.

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  7. scott_williams2

    scott_williams2 OBS Enthusiast

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    So I just changed it and the heat don’t work lol no difference. And one of those tabs was already broke and I broke another one but wit the bottom cover and the glovebox it doesn’t wiggle too much. I forgot to mention but the previous owner may have swapped in a lower thermostat. According to the The truck runs about 160 when warm and sometimes with hard running rises to 180. The gauge may be off idk what’s yalls opinion
     
  8. east302

    east302 I'm Awesome

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    Does the notched silver dial position indicator on the actuator respond to the head unit control? There are three tick marks at the 10, 12 and 2 o’clock positions. The notch will align with either the 10 or 2:00 at full cold or hot but I’m not sure which corresponds to which. The point is, make sure that it rotates freely through the full range.

    Back to what @Schurkey posted, do both heater hoses get hot? Not lukewarm, but too hot to hold for longer than, say, 5-10 seconds?

    Has the radiator been bled (engine cold, cap off, start it and run with the cap off until the thermostat opens, topping off and cleaning up the spills as you go).

    If this is a truck (not Suburban, Tahoe, etc.) then the hoses should go straight to the firewall with no heater valve. If there’s a valve or some monkeyed up fitting, it could possibly have the inlet/outlet reversed...

    Dash temperature gauge is pretty much for decoration only. My two 98s usually point to the halfway mark between 100 and 210, the tick marks are not linear so it’s likely not meant to be an accurate reading.
     
    Last edited: Nov 21, 2019
  9. scott_williams2

    scott_williams2 OBS Enthusiast

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    I’m lost. I’ve changed the actuator. It aligns wit the tick marks as it should both hoses get hot. I’ve changed the thermostat to a acdelco 195 and still no heat. The gauge still reads 160 warm what else could there be
     
  10. east302

    east302 I'm Awesome

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    Got a scanner? See what temperature the ECT sensor is reporting, it should be in the ballpark of the thermostat setpoint when warmed up.

    Are the hoses reversed?

    [​IMG]

    Any kinks or pinches in the hoses?

    Here are the pages from the manual (98) for heater diagnosis. Maybe something will stick out.

    Adjustments.jpg

    Adjustments.jpg

    Adjustments.jpg

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