January 30, 2008

Auto Tech: Heater woes

By Jim Kerr

Every January, I receive many calls, letters and e-mails from drivers concerned about the lack of interior heat in their vehicle. Sometimes there is a problem, but often the lack of interior heat is a result of changes in vehicle design. Let's look at what has changed.

To warm the interior of a vehicle, hot coolant from the engine is pumped through the heater core. The heater fan blows outside air over the fins on the heater core and the heat of the coolant is absorbed by the cool air. The heated air then enters the passenger compartment to provide passenger comfort.

Aluminum engine components are one of the design changes that affect interior heat. Aluminum transfers heat much more rapidly from the combustion chamber to the exterior surfaces of the engine. Many gasoline and some diesel engines use aluminum for cylinder heads, blocks, oil pans and engine covers. The heat transfers from these parts to the surrounding air, reducing the amount of heat that is transferred to the engine coolant.

So why use aluminum instead of cast iron for engine parts, as older vehicles do? Aluminum is lighter, and the lighter a vehicle the better fuel economy it can achieve. Aluminum is also easy to recycle, so many car parts are made from aluminum.

Improved fuel injection has also reduced engine heat. Burning fuel creates heat, but the more efficient an engine is, the less heat it produces. A vehicle with a load on the engine, such as when it is towing, accelerating or climbing a hill, will produce ample heat. The computer injects extra fuel to produce more power when a load is on the engine, and more heat is generated. Let that same engine idle, and very little fuel is used, so the engine and coolant cool off.

Port injection is more efficient than older throttle body injection systems, and direct gasoline injection is even more efficient. Diesel engines are about 30% more efficient than gasoline engines, so they produce even less heat, especially when idling.

Other engine design features also reduce engine heat output. Roller camshafts, roller rocker arms, low tension piston rings and special coatings on piston skirts all reduce internal engine friction. Variable cam timing and lift makes the engine more efficient, again reducing heat output. Modern vehicles may be more efficient and powerful, but they do produce less heat.

The thermostat is a critical part of any engine cooling - or heater system. The purpose of the thermostat is to prevent coolant from flowing through the radiator until the coolant in the engine is up to operating temperature. Then the thermostat will regulate coolant flow until all the coolant is up to operating temperature. Once all the coolant it at operating temperature, the thermostat remains fully open, allowing coolant flow through the radiator. If the thermostat opens at too low a temperature, or sticks in the partially open position, then the engine is very slow to warm up.

A thermostat can be tested by placing a fine wire between the valve and the body of the thermostat. Place it and a thermometer in a pot of water and heat them until the thermostat opens and falls off the wire. Note the temperature it opens at. Some thermostats open at 88 degrees C. Many are calibrated to open at 92 degrees C, while there are thermostats available for some vehicles that open at 95 degrees C. These ratings are often stamped on the thermostat body, so you can tell when it should open. If they open sooner, they should be replaced.

Operating the heater fan on low or medium speed will also warm the vehicle interior faster. Most drivers automatically turn the fan on high speed, but this blows so much cold air over the heater core and into the vehicle that the cabin is filled with cold air. As well, slower speeds allow more time for the incoming air to be heated by the heater core and keeps that warm air in the vehicle longer.

In extreme cold conditions, -30 to -40 C, a winterfront will help keep the heat where you want it. Look at the grilles on many current vehicles and you will see there are very small openings for the air to flow into the engine compartment. This reduces aerodynamic drag, but even these small openings allow a lot of cold air to blow across the engine when temperatures drop. A winterfront blocks the cold airflow so the engine retains more heat, but be sure to remove it when outside temperatures warm up or you may overheat your engine.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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