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I had the same problem. The answer to your problem is simple. You have an air pocket in your cooling system. Simple fix - take the radiator cap off of the radiator, turn the vehicle on and let it run for 1hr to remove the air from the system. Also, make sure your overflow container is atleast at the minimum level. Answer If your certain you have all of the air out of the cooling system the blend door inside the heater box may be stuck open.

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โˆ™ 2009-02-06 04:16:24
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Q: Why would a 1989 Chevy Silverado 350 heater only put out luke warm air even after changing the thermostat and back flushing the heater core?
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