How do you replace the coolant on a 2003 duramax?
remove pass side inner fenderwell. On the radiator you will see a drain. Loosen that and coolant will pour out. reinstall drain plug and top off with coolant approximatly 4 gallons.
Should be located in a removable housing at the engine end of the upper radiator hose Drain about 1 gallon of coolant from the radiator Remove this housing Note how thermostat is installed Clean both surfaces Replace thermostat and gasket Replace housing Start engine and look for leaks Run engine to normal operating temperature with heater on Re-check coolant level