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  1. #1

    Cool No heat up front, but heat in rear on '83 'burb


    First post, this board is great. I got an 83 C20 4x2 with the 454 for my birthday from the original owner. It's not a looker and needs a little TLC but overall runs like a champ. Truck was used to pull a horse trailer for its life and sat outside. Mechanically they took care of it, but i think I was the first person to vacuum the interior in several years. ;)

    The current mystery is the front heater. The blower works, but the heat never really gets hot. Oddly, if i switch to defroster the air coming out seems to be warmer, but its rarely, if ever hot. So i'm curious as to what might be causing it.

    Background: So far I've replaced the thermostat (thought maybe it was stuck open), temp gauge (broken) and rear heater core (leak made a mess out of cargo area), and redone the headliner (just proud).

    Info: when the rear heater was leaking, the coolant level was low, and so i figured that was probably it. now that that's fixed and the coolant level remains 'full' still the same problem. There's no (visible at least) coolant leak in the cab where the heater core is, but i haven't taken it apart to see as the coolant level stays good. The hoses going to from the heater core in the engine compartment are both hot. If i move the temp control from cold/hot, when its really cold out, it does get colder, so the damper seems to be working (at least some). And yes, I wait til the engine gets up to operating temperature (temp gauge pointing due north).

    All that being said, given enough time, the heater will heat up the truck, but it feels more like a heat pump (warmer enough to get the cab up in the 60's or 70's over enough time) but is never 'hot' (or warm even) if you stick your hand in front of it. By comparison, with the new core in the rear, when the truck is hot, if you turn the fan on, it blows hot air and the core gets VERY warm to the touch. (of course that motor had a short in it so i'm not using that til i can find a replacement, but i digress)

    Any ideas on what it might be and/or how to figure out what it might be?


  2. #2


    That's a stumper..... My best guess is that the damper door, while it may be moving, it may not be moving completely giving you only partial heat. Other than that, I have no clue what to do other than tear it down to the heater core and maybe replace it.


    '94 Chevy Suburban K1500
    3" exhaust w/ aero turbine non-baffled muffler
    CFM Technologies TB spacer
    CB w/ 44" whip antenna

  3. #3
    Master Mechanic
    Join Date
    Oct 2008
    Brandon, FLA
    Blog Entries


    If all components are getting hot, but air is not moving to the Hot side inside the Cab, I would also venture to say that the exchange doors are not fully operating correctly. How's the flow in the radiator? Go stream going by? Has the whole system ever been flushed?


  4. #4


    Exchange doors, eh? so... what/where can i find those? (I haven't taken apart the dash or engine side yet to look).

    A coolant flush, no. But when i replaced the heater core in the rear, i had to put in about 2.5 gallons of new coolant and when i did, to top it off, i saw that it was flowing around. I would say it was wooshing by the cap... but it was moving. I have no idea what rate it should move. I'm kinda new to this whole old truck thing... always been something i wanted to do, just never had the time til lately.

  5. #5


    If I'm not mistaken, the blend door is located in the box directly behing the glove box and is controlled by a cable. On my 78, the cable came off of the post on top of the box and so lost control of the door. Look in there and move the temp selector and see if you can find the cable and if it is still attached or not.

    99 K 1500 Suburban
    78 Silverado Big 10 w/factory 454
    00 S-10 Blazer
    1976 Trans Am
    1980 Honda CB900 Custom

  6. #6
    Master Mechanic
    Join Date
    Oct 2008
    Brandon, FLA
    Blog Entries


    Right On, GaryL. Its exactly where its located and some have the problem, some don't.....


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