The heater core is similar to a radiator and is a part of the vehicles coolant system hot coolant that has passed through other parts of the engine is run through the heater core as air is forced past it and into the cabin of the vehicle to heat it a clogged heater core will prevent the coolant from passing through it limiting the amount . Shop for new auto parts at 1aautocom http 1aauto c 87 d heater corein the video 1a auto shows how to flush your heater core list of tools usedo rubb. Best heater core flush works 100 of the time. 2003 ford explorer radiator sources https shrinkeim a9ewm 0 0 lv 4 9 years ago the best way if your going to do it yourself is to get a flushing t put into the heater core lines once you attach the t in the line then you can attach a garden hose and turn it on