Question about 2003 GMC Yukon XL
Heat blows only cold air
With engine warmed up, feel of heater hoses under hood to see if both are warm (careful don't burn yourself). If they both are warm, flapper door which directs airflow through heater is not working, probably because the actuator is bad or you have a vacuum leak. Check line under hood which goes to vacuum reservoir for vacuum, and check one way valve(check valve). Replace any old soft or cracked vacuum lines.
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Posted on Jan 02, 2017
SOURCE: Cold and no heat
This is a common complaint for the 4.3 v-6 by GM, what happens over time is air gets into the cooling system, usually a small coolant leak at the intake manifold gasket. Ait gets in the cooling system and starts electrolisis. From this the coolant starts to solidify. If I'm correct your heater core is plugged. Remove the radiator cap (engine cold only) and inspect the coolant. The proper color should be red. If the elctolisis is taking place the coolant will turn to rust and look like mudd. If you find mudd in the radiator, most likely the heater core is plugged. This is a very expensive repair. You'll need to remove the raditor & sent it out to be boiled out. Replace the heater core, thermostat and the coolant hoses. You'll also need to perform a "prestone" flush. You may need to flush the cooling system monthly until the system is clean.
Posted on Apr 15, 2009
you could have a couple things going on. possible low coolant? most likely cause as i assume you have checked coolant level would be heater core restricted. to fix this you remove heater hoses and back flush heater core with water. if this does not do it you may have a water pump not circulating at idle but this usually comes with vehicle running hot at idle.
Posted on Feb 16, 2010
Mine did the same thing you need to have heater core flushed out. Dexcool coolant clogs it up get it and the radiator back flushed and changed to regular coolant. This should fix the problem.
Posted on Oct 20, 2010
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This will help.Thanks.
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