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Hot/cold heater...HELP!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by lehtola, Mar 30, 2001.

  1. lehtola

    lehtola 1/2 ton status

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    I noticed over the last week-end that when I used my heater...it was blowing cold then hot then cold again. I don't think my thermostat is sticking and the engine temp is normal. What could this indicate?

    1990 GMC Jimmy 350/TH700R4/NP241/10 bolts, 4" skyjacker lift, 35x12.50R15 BFG All Terrains on 15x10 AR Baja's, Flowmasters.
     
  2. could be a clogged heater core. try flushing it out- you could take care of some cats at the same time-LOL. also make sure its not the thermostate. it could be stuck open. cheep and easy to replace. also- and this sounds really stupid, which means it's happened to me- make sure your coolent isn't low. if its really low-it's happened to me- it wont even make it to the heater core. good luck

    78, 350/350/203, 3/4 ton, 4" lift, 35" BFGs
    <A target="_blank" HREF=http://bluebeast.coloradok5.com/>http://bluebeast.coloradok5.com/</A>
     
  3. Sparky

    Sparky 1/2 ton status

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    San Antonio(summer) Texas A and M (school year)
    My guess is that you are low on coolant. Does it get cold wen you stop and then hot when you get moving again? This happens because at idle your water pump cant force much coolant into the heater core when not full of coolant. That is why when your truck overheats at idle sometimes it does no good to trun on the heater. Its just blowing air through an empty heater core.

    When all else fails... Check the blinker fluid.
    78 K-5
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Another vote for low coolant. Check the radiator and make sure it's full.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  5. freeforever

    freeforever 1/2 ton status

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    I had the same proble...low collant...I filled it and no proble....but you better check your radiator for a leak! Mine had one so I used Leake fixer stuff

    "Fool me once shame on you...fool me twice shame on me"
    ---------------
    "A closed mouth gathers no foot."
     
  6. lehtola

    lehtola 1/2 ton status

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    O.K. Thanks everyone...it was the low coolant. But now I think I have a leak.

    1990 GMC Jimmy 350/TH700R4/NP241/10 bolts, 4" skyjacker lift, 35x12.50R15 BFG All Terrains on 15x10 AR Baja's, Flowmasters.
     

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