170 Starting and driving

Economical motoring

Factors affecting fuel

consumption

Fuel consumption is greatly affected by the
general driving conditions, the way in which
the car is driven and at what speeds, the
weather, the state of the road, the condition
of the car, etc.

Breaking-in

Fuel consumption may be somewhat higher
during the break-in period (the first 3,000–
4,000 miles (5,000–7,000 km) than stated.

Weather conditions

Fuel consumption can be as much as 10 %
lower in summer than in winter. The higher
consumption in cold weather is explained by
the longer time it takes for the engine to
reach normal operating temperature, and
for the transmission and wheel bearings to
warm up. Fuel economy is also affected by
the distance driven: short journeys of
3–5 miles (5–8 km) do not give the engine
enough time to reach normal temperature.
Strong winds can also affect fuel con-
sumption.
How to read the graph above:
If fuel consumption with the engine at
normal temperature is 28 mpg
(10l/100 km), the actual fuel consumption 3
miles (5 km) after the engine has started
from cold will be:
– 23.5 mpg (12l/100 km) at outside temp.
of 68°F (20°C) (increase of 20 %).
– 17.7 mpg (16l/100 km) at outside temp.
of 32°F (0°C) (increase of 60 %).
– 14 mpg (20l/100 km)) at outside temp. of
–4°F (–20°C) (increase of 100 %).
As can be seen, both the distance travelled
by the car and the outside temperature have
a major impact on fuel consumption after
the engine has started from cold. Thus, if the
car is mainly used for short journeys of
3–5 miles (5–8 km), the fuel consumption
will be 60–80 % higher than normal.
IB311

Percentage increase in fuel consumption

of engine starting from cold compared to

engine at normal temperature

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