Owner's Manual Cadillac BLS - IFS Europe BV

460_OM_MY09.book Page 158 Wednesday, April 2, 2008 10:32 AM
158 Starting and driving
Economical motoring
Factors affecting fuel
consumption
The fuel consumption of a car is greatly
affected by driving conditions, climate, road
conditions, speed, driving technique, and so
on.
Running-in
Fuel consumption may be somewhat higher
during the running-in period (the first
3100-4350 miles/5000-7000 km) than
stated values.
Weather conditions
Summer temperatures give better fuel
economy that winter ones. The difference
can be as much as about 10 per cent. Consumption
increases in cold weather
because the engine takes longer to reach its
normal operating temperature. The transmission
and wheel bearings also take
longer to warm up. Even distance affects
consumption: short journeys of three to
five 3 to 5 miles (5-8 km) do not give the
engine enough time to reach its optimum
temperature. Wind conditions also have a
marked effect on consumption.
How to read the diagram (the following
example relates to petrol-engined cars):
If fuel consumption with the engine at normal
temperature is 28 mpg (10 l/100 km), the
actual fuel consumption 3 miles (5 km) after
the engine has started from cold will be:
– 23.5 mpg (12 l/100 km) at outside temp.
of +20 °C (increase of 20 %).
– 17.7 mpg (16 l/100 km) at outside temp.
of 0 °C (increase of 60 %).
– 14.1 mpg (20 l/100 km) at outside temp.
of –20 °C (increase of 100 %).
It is clear from the diagram that both distance
driven and outside temperature have
a significant impact on fuel consumption,
after a cold start.
If the car is normally driven on short journeys
of 3 to 5 miles (5–8 km), for example
to and from work, the average consumption
will be 60-80 per cent above the normal
level.
Percentage increase in fuel consumption
of engine starting from cold compared to
engine at normal temperature
Driving techniques
• To achieve the best running economy,
with regard to fuel consumption and general
wear, the car must be serviced regularly.
• High speed, unnecessary acceleration,
frequent braking and much changing
down all give higher fuel consumption.
• Frequent gear changing in traffic, starting
in cold weather, the use of studded tyres
and roof racks, and towing a caravan all
increase fuel consumption.