Question about 2000 GMC New Sierra 1500

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Lack of heat

Recently replaced thermostat...wondering if a possible blockage in heater core...can the intake and outtake hoses be switch to possibly dislodge the blockage without doing any damage to the core

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  • John Moreau Feb 18, 2009

    Thank you for all your help

  • yadayada
    yadayada May 11, 2010




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Switching the hoses is not recommended for trying to clear out a heater core because the coolant is meant to flow in one direction. you can try disconnecting the hoses from the heater core and flushing the core itself with a garden hose with low pressure in one direction for a few minutes and then switch and backflush the heater core. this is ok as long as the heater core is isolated from the engine cooling system. BUT if it is rusted pretty badly there is a chance it can develop a leak or blow out during the process so try it cautiously!! if the core is in-fact blocked you will have very little flow through the core and you will see what looks like rust coming out of the core, it may take quite a few times switching back and forth to clear it out. if it still remains blocked or if it starts leaking inside the car it will need to be replaced.

Posted on Feb 17, 2009


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