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Gmc 6.5 diesel heating

Discussion in 'Trucks' started by HEAVY386, Dec 14, 2011.

  1. HEAVY386

    HEAVY386 Member

    Joined:
    Mar 4, 2010
    Messages:
    13
    Occupation:
    MOBILE EQUIPMENT MECHANIC
    Location:
    Pleasant valley NY
    I have a 1999 gmc heating fine driving down the road or with idle up but let off at a light and heater drops off fast temp. gauge reads normal but no heat , tried bleeding several times still not much better any help ?
     
  2. jrtraderny

    jrtraderny Well-Known Member

    Joined:
    Nov 26, 2006
    Messages:
    230
    Location:
    New York
    Might be the heater core's starting to plug, also could be the water pump impellor is beginning to wear away from corrosion.
     
  3. daman

    daman Well-Known Member

    Joined:
    Mar 22, 2010
    Messages:
    237
    Occupation:
    Agriculture,Truck Driver,Mechanic
    Location:
    Bad Axe,MI
    Try back flushing the heater core good. or is coolant level low??
     
  4. FSERVICE

    FSERVICE Senior Member

    Joined:
    Apr 2, 2009
    Messages:
    635
    Location:
    indiana
    you say tried bleeding. was the system opened for service/replace componet? that has 2 tstats could b one stuck open happened on mine. does it take a while to warm up?
     
  5. Sparkie

    Sparkie Well-Known Member

    Joined:
    Aug 3, 2011
    Messages:
    50
    Location:
    Cyrus MN
    Pull it out, throw it in the garbage, and put a 454 in it.
     
  6. barklee

    barklee Senior Member

    Joined:
    Aug 4, 2009
    Messages:
    903
    Location:
    ohio
    Bet your heater core is fried..... had a f-800 ford do the same thing. Couple weeks later the core cracked a leak.
     
  7. smokey1

    smokey1 Well-Known Member

    Joined:
    Jan 12, 2009
    Messages:
    114
    Occupation:
    Builder/Owner
    Location:
    West Bridgewater,MA.
    pull the hoses off the heater and hook together. the hoses should get real hot, this will eliminate a pluged heater core
     
  8. surfer-joe

    surfer-joe Senior Member

    Joined:
    Mar 25, 2007
    Messages:
    1,403
    Location:
    Arizona
    6.5s have real problems with coolant pumps. There is a replacement that works better and lasts longer. Check with your dealer. You may also have a problem with temp regulator, or with heater core.

    6.5 is not a bad engine, properly maintained and set up. (I have two) Both of mine have improved turbos, performance chips, many mods inside the engine itself, and will run on nearly anything you can put in the fuel tank. I run B99 often, but also #2, or #1 if it gets real cold. No additives. Both units also exhaust via 4" tubing and freeflow muffler. Newer one has a cat off an 08 Duramax, just for visual effect at emissions test station.

    Last but not least, get online with the 6.5 diesel forum. http://www.sixfiveturbodiesel.com/ There you will find many answers to 6.5 problems, and the vehicles they are installed in.

    Good Luck!