A clogged heater core in your Dodge Durango will lead to problems with your air heater system, as well as problems like leaking coolant. It may be possible to flush out the core to get it working again, rather than undertaking the painstaking process of completely replacing the core. This is only if the core is not excessively clogged, so you need to do this as soon as you are sure of the problem. This process is much like flushing a core for any other vehicle.
Drain the engine coolant at the radiator, opening the drain fitting -- you may need pliers for this -- and draining it into a large container. Connecting a 3/8 inch diameter hose to the drain fitting can help direct the flow.
Loosen the hose clamps on the heater hoses and disconnect them from the engine side firewall. The hose clamps on this model should take pliers or a screwdriver. Plug the hoses with rubber or something similar to prevent dirt from getting in.
Connect a garden hose to one open end on the firewall. Make sure this hose is connected to a working faucet.
Turn on the faucet and let the water run through to the heater core. Look for the water, coolant and other contaminants to come out the other opening in the firewall.
Wait for nothing but clear water to come out the opening, then shut off the water and disconnect the hose from the firewall.
Reconnect the heater hoses to the firewall -- make sure you connect each hose to the same fitting as before.
Refill the radiator and coolant tank with a fresh mix of coolant/antifreeze and water (a straight 50/50 mix is usually needed). Check your Durango's manual for the exact type of coolant needed, as you should never mix coolants.
