by D. O'Larde

Created on: October 25, 2008

Next to driving less, driving slowly is one of the easiest ways to save gas. To appreciate it more fully it is good to know how driving slowly saves gas. When you start an internal combustion engine the starter motor cranks the engine to get the air-fuel mixture into the combustion chambers and it gets ignited by the spark plugs. The combustion that occurs powers the pistons and continues running the engine in a cycle as long as there is an uninterrupted supply of fuel. The engine is now idling with the purpose of just warming the engine and not really moving the vehicle an inch. This is your first opportunity to save gas by getting on gear right away and drive slowly. Drive slowly for as long as you are not obstructing traffic while warming your engine not only for a more efficient operation of the engine but also to save on gas.

The speed of a vehicle is controlled primarily by the rate of air-fuel mixture being fed into the combustion chambers. The opening and closing of the throttle valve which is linked to the accelerator pedal controls the rate or amount of air-fuel mixture that enters the intake manifold distributing it to the four, six, or eight combustion chambers depending upon the number of cylinders in the engine. An idling engine has the throttle valve at its closed position and the idling system or low-speed system covers the fueling of the idling. At speeds of up to approximately 25 mph the idling or low-speed system takes care of feeding fuel to the engine. This system comes into play when you coast along as you approach a traffic stop sign and this is a significant part of the "driving slowly to save gas" campaign. At speeds beyond approximately 25 mph you step more on the pedal to accelerate, gradually opening the throttle valve as you gather speed. Depressing the accelerator pedal opens the throttle valve to allow an increased rate or amount of air-fuel mixture to reach the combustion chambers.

Perhaps for some it might help to illustrate why more fuel is needed at increased speed than at a slow speed when driving a vehicle. Consider a vehicle without the engine running that you want to push uphill from point A to point B. You may be strong enough to push it from point A to point B but not as fast as when you have some additional strength or extra bodies. You can drive uphill slowly with so much rate of fuel consumption but when you want to double your speed you need to depress the accelerator pedal to open the throttle valve more and double your rate of fuel consumption.

Lastly, it might be worthwhile to note that when you want to save gas by driving slowly you must not do it in the freeways where speed is the name of the game. Drive at a speed that will not jeopardized safety on the road. There are a lot more slow-driving opportunities in city streets than in the freeways. Exercise discretion when driving slowly to save gas.

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