Engine coolant passes through the heater core to generate warmth for the interior of your 2000 Chevrolet Silverado. The core can be clogged, causing the heater to malfunction and the coolant to leak. If this happens, you can fix the problem by flushing out the core. If you cannot flush the heater core, it's likely that it's so clogged or damaged that you'll have to replace it.
Place a large container underneath the radiator's drain plug, which is at the lower corner.
Twist and remove the plug to drain the engine coolant into the container. Check the coolant's condition; it's likely that the coolant is contaminated and you'll have to replace it.
Disconnect the heater hoses at the engine compartment firewall, loosening their hose clamps with pliers. Apply the clamps to the disconnected hoses or plug them to prevent contaminants from entering.
Insert the end of a garden hose that's connected to a working faucet into one of the heater core openings on the firewall.
Turn the faucet on and look for the water to flow from the other heater core opening. Let the water run until it is clear. Shut off the faucet and remove the hose. If the water doesn't flow steadily, try the other opening.
Reconnect the hoses to the connections at the firewall using their clamps, making sure each hose connects to the correct fitting.
Fill the radiator with a fresh 50-50 mix of water and either green glycol-based antifreeze or orange silicate-free antifreeze.
