The engine should be warmed up before driving.
True, the engine must be warmed up, but idling is not an effective
way to warm up your vehicle, even in cold weather. The best way to
do this is by driving the vehicle. With today's modern engines, and
the advent of electronic engines, you need no more than about 30
seconds of idling before driving away, even on the coldest winter
Idling is good for your engine.
Excessive idling can actually damage your engine components,
including cylinders, spark plugs, and exhaust systems. An idling
engine is not operating at its peak temperature, which means that
fuel does not undergo complete combustion. This leaves fuel residue
that can condense on cylinder walls, where they can contaminate the
oil and damage parts of the engine. For example, fuel residues are
often deposited on spark plugs. As you spend more time idling, the
average temperature of the spark plug drops. This makes the plug get
dirty more quickly, which increases fuel consumption by four to five
percent. Excessive idling also lets water condense in the vehicle's
exhaust, leading to corrosion and can reduce the life of the exhaust
Shutting off and restarting your vehicle is hard on the engine.
Frequently restarting has little impact on engine components like
the battery and the starter motor. Component wear caused by
restarting the engine is estimated to add $10 per year to the cost
of driving, money likely to be saved many times over due to fuel
Shutting off and restarting your vehicle uses more gas than if you
leave it running.
The bottom line is that over 10 seconds of idling uses more fuel
than restarting the engine. As a rule of thumb, if you are going to
stop for 10 seconds or more - except in traffic - turn off the
engine. You'll save money, and you won't produce harmful Carbon
Dioxide, the leading greenhouse gas.