On The Road

Getting to the core of the problem

We had a car dropped off last week with a coolant leak on the inside of the passenger footwell. Typically when we see coolant leaking into this area, it’s coming from the heater core. Sure enough, that’s what happened in this case, so we replaced the heating core.

That prompted me to write this month’s column on the heater system (I discussed air conditioning last month), even though fall hasn’t arrived just yet. The heater system isn’t as complicated as the air-conditioning system, but they share some common components.

Before we go any further, let me explain how the heater works. The system is tied into or piggy- backs on the engine’s cooling system. The engine water pump circulates coolant or antifreeze through the engine so that it does not overheat. After the hot coolant leaves the engine, it can be transferred to other parts of the powertrain to use the heated coolant – including to the passenger compartment heater core.

Just like the engine’s radiator, air-conditioning condenser and air-conditioning evaporator, the heater core is a heat exchanger. The hot coolant flows from the engine’s coolant return line into the heater control valve. If the valve is closed, the hot coolant will not enter the heater core; if it is open, it will flow through the heater core.

The heater core sits inside the heater box with the blower motor and the air-conditioning evaporator. If the heater valve is open and the fan is turned on, the blower will push cold air across the heater core and it will exit your dash vents nice and warm. The coolant then just leaves the heater core and goes back into the engine’s coolant return line.

There are a few engine components that also use the hot coolant. The idle air control valve (IAC) and the throttle body use the hot coolant to stay warm. Because the IAC and throttle body are computer controlled, it is important they keep warm or at operating temperature.

If you lived in a cold climate, the IAC needs to stay warm to properly adjust the idle speed of the car. It is also the same for the throttle body. If the throttle plate were to freeze, the car would be unable to accelerate or decelerate.

The heater core also can cause more problems than a coolant leak. Over time, dirt and calcium can build up inside the heater core and cause blockages. A blockage in the heater core can affect the amount of heat coming into the cabin, and it also can affect the engine’s coolant system. Even a partial blockage can create an air pocket in the engine’s coolant system that could lead to the engine overheating. So if you have ever had a strange or unexplainable engine-overheating problem, the heater core could be the culprit.

Replacing a heater core is an expensive and time-consuming repair. If you are in a time crunch or need to save money, the heater core can be bypassed. The car will just not have any heat until it is replaced.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email This email address is being protected from spambots. You need JavaScript enabled to view it. or visit sunnyvaleforeigncar.com.

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