Environmental Myths

Starting an Engine Consumes More Energy Than Running it

There is a widespread belief that starting an internal combustion engines consumes more energy that when it is running. Most of the time, this belief is false. Those who hold this belief will be found to idle their engines for long periods, wasting fuel and producing emissions needlessly.

How did This Myth Come About?

Many years ago, cars (automobiles) had a manual choke for starting a cold engine. This was usually on a pull button or a lever. Its purpose was to make the combustion mixture richer in fuel in order to make starting easier. As this was a manual process, some skill would be needed to only use as much choke as necessary to produce a quick start of the internal combustion engine.

If insufficient choke was applied, the air and fuel mixture would not burn. The air and unburned fuel would leave the engine and enter the atmosphere via the exhaust pipe. Thus, the energy giving effect of the fuel will have been completely wasted.

Similarly, if to much choke was applied, the air and fuel mixture would burn erratically. Sometimes, the fuel would condense in the cold engine resulting in a condition known as a flooded engine. To overcome the problem of a flooded engine, the choke would have to be turned off and the engine turned over many times to flush the fuel from the engine's cylinders. Then another attempt to start the engine with the choke could be made. Whenever the engine was not starting, air and unburned fuel would leave the engine and enter the atmosphere via the exhaust pipe. Thus, the energy giving effect of the fuel will have been completely wasted. In the case of an engine that started with too much choke, some of the fuel would not have been burnt and this fuel would leave the engine and enter the atmosphere via the exhaust pipe.

Getting the choke setting right is a skill. Without that skill, fuel is wasted and this may have been the source of the myth that starting an internal combustion engines consumes more energy that when it is running.

With manual chokes there is a reasonable likelihood that fuel will be wasted when starting a car. Nowadays, cars have automatic chokes fuel is used more efficiently with less waste.

Crushing the Myth

When starting an engine without any choke and without any throttle, the rate of fuel usage is no more than an idling engine. When a modern engine is warm, there is no need to start an engine with choke or throttle. To use choke or throttle with a warm engine is a bad practice as it is unnecessary.

When starting a cold engine with the choke, the rate of fuel usage is more than an idling engine. However, the choke should be reduced immediately after starting and will be switched off completely after a minute or two. With an automatic choke the reduction and switching off is done as quickly as possible. With a manual choke it is likely that it the choke will not be reduced as quickly as an automatic choke but, using good practice, will be switched off after a minute or two of starting the engine.

So, leaving an engine to idle for more than a minute will use far more fuel than switching the engine off for over a minute before restarting it.

Of course, some energy will be used by the starter motor to restart the engine and there will be more wear and tear on the starter motor and battery, but these are insufficient to the fuel wasted by an engine idling for more than a minute.

What is also very bad for the environment is to have an engine idling with the air conditioning on. Air conditioning requires far more fuel to keep the engine idling than is required for an unloaded engine.

Switching on Fluorescent Lights uses Large Amounts of Energy

There is a widespread belief that fluorescent lights, and low energy lamps, use vast amount of energy when they are switched on and thus should always be left on. This is only partly true.

How did This Myth Come About?

Fluorescent lights need to be warm to get them started. Many people would be aware that fluorescent tubes are associated with a choke or starter. When a fluorescent tubes starts, it tend to flash several times before it stays on. It is not unusual to see the choke flash when the fluorescent tube flashes. This gives the impression that vast amounts of energy is being used.

Crushing the Myth

Fluorescent lamps need to be warm to get them started. During the first few seconds, power is used to heat up the lamp. Once warm, the electrical circuit changes to try and light the lamp. If it succeeds, the lamp will remain warm enough to keep lit. If fails, the lamp will probably flash and power will be returned to warm the lamp before trying to light the lamp again.

If the power to warm the lamp is 10 times the power to keep it lit and it takes 10 seconds before the lamp is lit then the power used to light the lamp is equivalent to running the lamp for 100 seconds. Or, to put it another way, if the lamp is switched off, it would need to be left off for more than 100 seconds before being switched on again in order to use less electricity than leaving the light on.

Now, the power to warm most fluorescent lights is less than 10 times the power to keep it lit and takes far less than 10 seconds before the lamp is lit. So, if the area the lamp lights is not going to be used for more than two minutes it is worth switching the lamp off.