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Your Heat Exchanger (Heater Core) worn out? » Read more about common malfunctions • Repair • Replacement manual
Warm interior with the heater core
Heater core (also called "interior heater" or "heat exchanger") is the central component for the heating system of the car interior. It is in fact a simple heat exchanger just like the engine radiator. The heater core is connected to the engine cooling system. The residual heat for the interior is thus generated cost-neutrally.
Heater core: construction, function and location
The heater core is a winding copper tube covered with aluminium fins. Heated coolant runs through the tube, allowing the aluminium fins to absorb the heat. A fan blows through the tubing, directing the heat into the car interior. The heater core can be manually disconnected from the cooling circulation allowing the driver to control the interior heating. In the past this was done by mechanical regulators. Nowadays, for reasons of comfort electronically controlled valve flaps are used. The heater core is located in a welded pocket between bulkhead and dashboard, only accessible from the interior. Although the heater core as a spare part is really cheap, the amount of work required for its replacement makes it expensive.
Heater core defects
A heater core can get leaky due to old age. If the engine is cooled with water instead of the prescribed antifreeze mix, the heater's copper will corrode. Rust from other parts of the cooling circuit, deposited in the heater core speed up the corrosion. The alternating temperatures in the engine compartment as well as vibrations can cause leakages of the core's flanges. The symptom indicating a defective heater core is unmistakable: the windshield fogging up on the inside. A deteriorating cooling performance is another symptom. Fogged windshield are typical in this case. A defective heater core is not just simply a loss of comfort during driving. The moisture leaking from the heat exchanger can cause serious damage to the dashboard electronics. This is likely to result in continuous coolant leakage, in which case sooner or later, coolant flows into the footwell of the car. When the driver's or passenger's feet get wet, the situation must be inspected without delay. The heater core is connected to the car's cooling circuit; therefore leakage can be identified by its typical smell and colour. A hankerchief test can give certainty. If it turns the same colour as the coolant after mopping, the cause is found. If the water is clear without any smell, a clogged drainage or a leaking door rubber can be the cause for water in the interior.
Heater core: repair
As for all cooling circuit leakages there is only one reliable option: replacement of the defective component. We strongly advise against using radiator sealing additives. They only clog the cooling ducts and impair the entire system's cooling performance. In case of the heater core this means disassembly of the entire dashboard. Nowadays, all cars are equipped with driver and passenger airbags. Therefore this repair is not without risk. Prior to removal of the steering wheel and dashboard, inform yourself thoroughly on de-activating the airbags. For all extensive repairs, the battery should be disconnected. Disassembling the dashboard takes up to 2 – 3 hours. Be sure to make pictures of every step, no matter how insignificant. This specifically applies to the screw connections and the electronic wiring. Once this is done, the heater core is quickly replaced. Its spare part costs ca. 15 EUR (± £13). The heater core is located in a welded pocket and can be pulled out. When disconnecting the hoses, their condition should be checked as well. In case they are clogged with calcium deposit and cracked, hoses must be replaced as well. An additional £4 per hose is not really very expensive. A disassembled dashboard is a perfect occasion for an upgrade. By replacing all lamps by LEDs, you obtain permanent and reliable interior lighting, causing you no trouble ever again. The dashboard's assembly is likely to take another 4 hours. Now, the picture documentation comes in really handy and can make the work a lot easier.