Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hi There, I'm Clay a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
From your description most likely there is low flow through the heater core when the vehicle is at idle. Both heater hoses should be hot when the engine coolant is at least 180°F. You can back flush the heater core and see is the heaters performance improves. Also inspect the radiator tank nipple that feeds the surge tank. If the radiator is missing the surge tank restriction orifice, there will be an increased amount of coolant flow to the surge tank. The restriction orifice is molded into the nipple that feeds the radiator surge tank. The restrictor orifice is recessed approximately 2" inside of the nipple, is 5/64" in diameter.
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