536 | Thermodynamics
Use the Air Conditioner Sparingly
Air-conditioning consumes considerable power and thus increases fuel con-
sumption by 3 to 4 percent during highway driving, and by as much as 10 per-
cent during city driving (Fig. 9–65). The best alternative to air-conditioning is
to supply fresh outdoor air to the car through the vents by turning on the flow-
through ventilation system (usually by running the air conditioner in the
“economy” mode) while keeping the windows and the sunroof closed. This
measure is adequate to achieve comfort in pleasant weather, and it saves the
most fuel since the compressor of the air conditioner is off. In warmer weather,
however, ventilation cannot provide adequate cooling effect. In that case we
can attempt to achieve comfort by rolling down the windows or opening the
sunroof. This is certainly a viable alternative for city driving, but not so on
highways since the aerodynamic drag caused by wide-open windows or sun-
roof at highway speeds consumes more fuel than does the air conditioner.
Therefore, at highway speeds, the windows or the sunroof should be closed
and the air conditioner should be turned on instead to save fuel. This is espe-
cially the case for the newer, aerodynamically designed cars.
Most air conditioners have a “maximum” or “recirculation” setting that
reduces the amount of hot outside air that must be cooled, and thus the fuel
consumption for air-conditioning. A passive measure to reduce the need for
air conditioning is to park the vehicle in the shade, and to leave the windows
slightly open to allow for air circulation.AFTER DRIVINGYou cannot be an efficient person and accomplish much unless you take good
care of yourself (eating right, maintaining physical fitness, having checkups,
etc.), and the cars are no exception. Regular maintenance improves perfor-
mance, increases gas mileage, reduces pollution, lowers repair costs, and
extends engine life. A little time and money saved now may cost a lot later in
increased fuel, repair, and replacement costs.
Proper maintenance such as checking the levels of fluids (engine oil, coolant,
transmission, brake, power steering, windshield washer, etc.), the tightness of
all belts, and formation of cracks or frays on hoses, belts, and wires, keeping
tires properly inflated, lubricating the moving components, and replacing
clogged air, fuel, or oil filtersmaximizes fuel efficiency (Fig. 9–66). Clogged
air filters increase fuel consumption (by up to 10 percent) and pollution by
restricting airflow to the engine, and thus they should be replaced. The car
should be tuned up regularly unless it has electronic controls and a fuel-
injection system. High temperatures (which may be due to a malfunction of
the cooling fan) should be avoided as they may cause the break down of the
engine oil and thus excessive wear of the engine, and low temperatures
(which may be due to a malfunction of the thermostat) may extend the
engine’s warm-up period and may prevent the engine from reaching the opti-
mum operating conditions. Both effects reduce fuel economy.
Clean oil extends engine life by reducing engine wear caused by friction,
removes acids, sludge, and other harmful substances from the engine, improves
performance, reduces fuel consumption, and decreases air pollution. Oil also
helps to cool the engine, provides a seal between the cylinder walls and theFIGURE 9–65
Air conditioning increases fuel
consumption by 3 to 4 percent during
highway driving, and by as much as
10 percent during city driving.
FIGURE 9–66
Proper maintenance maximizes fuel
efficiency and extends engine life.