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How to Flush a Heater Core

Omkar Phatak
If you are looking for guidelines on how to flush a heater core in a car, this story will be an instructive read. Here I shall provide you with a step by step procedure for heater core flush.
If you turn on the car heater and find cold air being blown in through the vents, this is a classic symptom of car heating system breakdown. You can put off doing anything about it in summer, but once winter sets in, having a compromised heating system in your car, can turn it into an iceberg when driving in snow! In old cars, the most common cause of a heater breakdown is a blocked heater core.

Role of the Heater Core

If you are attempting a heater core flush for the first time, it would be instructive to know what is the role of the heater core in the functioning of the heating system. The heater core is a metal contraption with inner pathways in the form of tubes for coolant flow and fins to radiate heat.
The heat transported by circulating air from the heater core, into the car interiors is derived from the car engine itself. The coolant that is constantly circulated around the car engine to keep its temperature down is passed through tubes in the heater core.
The heat transported from the engine is thus received by the core, which causes it to heat up. A blower fan attached next to the heater core, passes warm air into the car interiors through vents. The heating system operation is controlled by thermostats fitted inside, which operate valves that control coolant flow.
Most of the time, the core gets clogged due to debris, leading to a failure of heating action. One of the simplest ways of taking care of this problem is flushing the core. Let us take a look at the correct procedure to flush a heater core.

How to Flush a Heater Core?

You will need a fresh can of engine coolant fluid, buckets, a garden hose and plenty of rags for cleaning up later. Let the car cool down in shade for a few hours before you begin the procedure. Park it at a location, where your garden house can reach it easily.
First thing you need to do is find the inlet and exit hoses of your heater core, that supply the coolant fluid. The heater core is situated below the dashboard of your car and the inlet and exit hoses are connected to the core, through the firewall. Look for rubber hoses going into the firewall, connected with clamps. Once you have located them, drain the coolant fluid from the radiator by unplugging it. Use a bucket to collect all the coolant drained from the radiator.
Once you are done with the draining, remove both the inlet and outlet hoses attached to the heater core, by removing the clamps attached to them. Connect the garden hose and insert its other end into the outlet where the coolant exit hose was previously connected. Let water course through the inlet, into the core and out of the inlet valve at low pressure.
Arrange another hose to collect the water from the inlet valve into a bucket. Continue flushing for 10 to 15 minutes. After all the inner debris has been cleared out, remove the hose and switch off the tap.
Reconnect the inlet and outlet hoses of the heater core as they were connected before. Open the can of coolant fluid and top off the radiator with fresh coolant fluid back again. With that, your job of heater core flushing is complete. Clean any water or coolant that might have spilled around. Operate the heating system and check if its functioning is back to normal.
If you can feel the car interiors getting warmer, your objective has been accomplished! If you find that flushing doesn't improve the functioning of the heater system, you may have to go for a heater core replacement. Also get the thermostat, electronic valves, blower motor and radiator checked.
The procedure is extremely simple if you concentrate on flushing just the heater core, instead of flushing the entire system. You need to be careful if you plan to flush the entire heating system, along with the radiator.
If you are not confident of pulling off the whole thing, you can always let an expert car mechanic handle it, who will finish the job in flat 20 to 30 minutes. Just make sure that you dispose of the old coolant fluid properly and don't leave it lying around.
Make the heater core checkup, a part of your regular car maintenance schedule. A periodic flushing of the core will prevent debris from clogging up the core and lengthen its life.