Katerina Swanson
There is a common misconception that leaving a car idling uses less fuel than turning the engine off and on again. This was true for older cars that used carburetors, which required a significant amount of gas to start the engine. However, modern cars use fuel injection, which delivers precise amounts of fuel only when needed, meaning that newer cars use very little fuel on startup.
Do newer cars use much fuel on startup?
| Characteristics | Values |
|---|---|
| Fuel consumption during startup | Newer cars with fuel injection systems use less fuel during startup than older cars with carburetors. |
| Idling fuel consumption | Idling fuel consumption is higher than startup fuel consumption in newer cars. |
| Engine wear | Frequent restarting has little impact on engine components like the battery and starter motor. |
| Fuel savings | Turning off the engine for stops longer than 30 seconds can save fuel. |
| Air quality | Turning off the engine instead of idling reduces tailpipe emissions and improves air quality. |
| Engine lubrication | Starting a cold engine can cause bearing and parts wear due to lack of lubrication. |
| Fuel pump lubrication | Running the fuel pump without enough fuel can cause overheating and damage. |
| Engine damage | Burning a lean air-fuel mixture can cause explosions within the cylinders, damaging spark plugs and engine valves. |
| Fuel efficiency | Newer fuel-efficient hybrids and start/stop systems improve fuel efficiency by shutting off the engine when idling or stopped. |
| Engine temperature | Engines operate in open-loop mode during cold starts, using pre-programmed values to ensure reliable starting and minimize engine damage. |
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What You'll Learn
Fuel injection systems
Modern fuel injection systems have had a profound impact on how the combustion engine works. All compression-ignition engines (e.g. diesel engines) and many spark-ignition engines (i.e. petrol engines) use fuel injection. Fuel injection systems provide lower fuel consumption, more power, increased reliability, and a massive future opportunity over the carburetor.
Fuel injection has been around since the 1950s and was first mass-produced for diesel engines in the late 1930s and early 1940s. In the 1950s, fuel injection was introduced in passenger car petrol engines and gradually gained prevalence until it had largely replaced carburetors by the early 1990s. The first mass-produced petrol direct injection system for passenger cars was a common-rail system introduced in the 1997 Mitsubishi 6G74 V6 engine.
The fundamental function of a fuel injection system is to ensure the accurate mixture and delivery of fuel to the combustion chamber. Modern fuel injection systems use a computer, oxygen sensor, injectors, a fuel pump, and pressure regulators to ensure the accurate mixture and delivery of fuel to the combustion chamber. The computer can correct the length of time the injector is held open if there is too much fuel. Carburetors, on the other hand, rely on suction created by intake air accelerated through a Venturi tube to draw fuel into the airstream.
There are four basic types of modern fuel injection: single-point, multi-port, sequential, and direct injection. Single-point injection, also known as central fuel injection, incorporates electrically controlled fuel injector valves into the throttle body. Multi-port fuel injection, also known as port, multi-point, or sequential fuel injection, has a fuel injector for each cylinder, usually located so that they spray right at the intake valve. These systems provide more accurate fuel metering and a quicker response. Direct injection can be achieved with a conventional helix-controlled injection pump, unit injectors, or a common-rail injection system, the last of which is the most common system in modern automotive engines.
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Carburettors vs fuel injection
The debate between carburettors and fuel injection systems has been ongoing, with car enthusiasts holding conflicting opinions about the pros and cons of each system. Carburettors were the most prevalent fuelling system used in cars, motorcycles, and planes until the introduction of fuel injection.
A carburettor uses a Venturi Tube that creates a vacuum, pulling in fuel. The ratio of air to fuel is then adjusted using two valves: the choke and the throttle. The choke decreases the amount of air and increases the flow of fuel, which is useful for cold starts. The throttle valve, or butterfly valve, regulates how much of the air-fuel mixture flows into the engine, controlling the car's response. Carburettors are simple and straightforward, but they can be uneven in their fuel delivery, inefficient, and struggle with changes in altitude.
Fuel injection systems, on the other hand, precisely measure and time the injection of fuel into the intake manifold or combustion chamber. This accuracy allows for optimal air-fuel ratios, improving combustion and increasing power output and fuel economy. Fuel injection systems can also adjust to environmental factors like temperature and altitude, ensuring consistent performance. Electronic fuel injection (EFI) systems use sensors to monitor engine characteristics and modify the fuel supply, improving performance and reducing emissions.
Fuel injection systems offer increased fuel efficiency, smoother acceleration, and higher power output compared to carburettors. They also help engines last longer and are essential for meeting strict emissions standards. While carburettors are simpler and easier to repair, fuel injection systems provide better performance, fuel economy, and are more adaptable to changing conditions.
Regarding fuel consumption during startup, newer cars with fuel injection systems use minimal fuel during the shutdown/startup process, equivalent to about 2-3 seconds of idling. This is in contrast to older cars with carburettors, which used a significant amount of fuel during engine startup, leading to the practice of leaving cars idling instead of turning them off. Today, many newer cars have a start/stop function, automatically shutting off the engine when the car is not in motion to save fuel.
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Engine lubrication
The main challenge with engine lubrication during startup is the low temperature of the oil, which affects its circulation and ability to reach optimal pressure. Oil needs to be at the right temperature and pressure to effectively protect the engine. It takes a minimal amount of time for the oil to reach pressure when the engine first starts, but it can take around 10 minutes for the oil to warm up to its optimum temperature. This delay in reaching optimum temperature results in a period of low pressure during startup, where crucial lubrication is lacking, leading to increased wear.
To address this issue, some technologies such as "block heaters" can be used to pre-heat the oil before starting the engine. These heaters rely on a mains power cable and need to be switched on about half an hour before driving. While most manufacturers do not include these technologies, they can be installed as aftermarket items. Another solution is to use a pre-oiler, which is a cheaper option that can double or triple engine life. By pre-charging the pre-oiler with compressed air, the oil can be pushed into the engine to pre-lubricate the moving internal components before starting it for the first time.
In addition to these solutions, specific additives have been incorporated into engine oils to reduce startup wear by nearly 30%. These additives ensure that a film of lubricating oil exists between moving parts to decrease friction and wear during startup and operation. Oil pumps in modern engines circulate oil for lubrication and cooling while also powering hydraulic components associated with timing belt tensioners and variable valve timing solenoids.
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Fuel efficiency
Fuel Injection Systems
Newer cars are now equipped with computer-controlled fuel injection systems, which deliver precise amounts of fuel directly to each car engine cylinder when required. This system ensures that only a minimal amount of fuel is used during the shutdown and startup processes, equivalent to around 2-3 seconds of idling. This is in contrast to older carburetor systems, which required a significant amount of gas to start the engine, making it more fuel-efficient to keep the engine idling rather than turning it off.
Idling vs. Starting Up
There is a common misconception that leaving a car idling uses less fuel than turning it off and starting it up again. However, this is not true for newer cars with fuel injection systems. In fact, idling for more than 30 seconds can use more fuel than simply turning off the engine and restarting it. This is because fuel injection systems provide the correct fuel-to-air mixture from the moment the engine is started, ensuring efficient fuel usage.
Engine Warm-Up
It is worth noting that a cold engine may use more fuel during the initial warm-up period. This is because the engine management software operates in an open-loop mode, using pre-programmed values to determine fuel usage and spark advance until the engine is up to temperature. However, this does not negate the fuel savings of turning off the engine instead of idling. Additionally, frequent restarting has been shown to have little impact on engine components, and modern cars are often equipped with an engine "sleep" mode, which automatically shuts off the engine when the car is stopped.
Other Factors
It is important to consider other factors that can affect fuel efficiency, such as engine size, the number of cylinders, and tuning. Additionally, the type of fuel injection system and engine management software can also play a role in fuel efficiency. Overall, newer cars with fuel injection systems are designed to be more fuel-efficient during startup and idle, and turning off the engine for short periods can further improve fuel savings.
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Engine temperature
However, modern vehicles have replaced carburetors with fuel injection systems, which electronically regulate the air-fuel mixture. This advancement ensures that only the required amount of fuel is supplied during startup, significantly reducing fuel consumption. Additionally, the ECU in newer cars provides just enough fuel to manage the cranking speed RPMs and idle speed RPMs during startup, minimizing excess fuel usage.
The impact of engine temperature on fuel consumption is particularly noticeable in cold climates. Cold engines require more fuel to reach their operating temperature, and the difference in fuel usage between a cold and warmed-up engine can be significant. Thus, letting a cold engine warm up before driving can help optimize fuel efficiency.
It is worth noting that while newer cars with fuel injection systems have improved fuel efficiency during startup, there is still a trade-off between fuel economy and emissions. Turning off an engine for a brief period can save fuel but may increase tailpipe emissions due to the catalytic converter cooling down and producing higher levels of NOx and CO upon restart. Therefore, the optimal approach may vary depending on environmental conditions and regulations.
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Frequently asked questions
Newer cars are more fuel-efficient and employ a computer-controlled fuel injection system that delivers precise amounts of fuel to each car engine cylinder only when needed. On average, it takes about half a teaspoon of gas to start the engine.
Older cars used a carburetor system to spray fuel into the airstream feeding the engine, which required a lot more fuel on startup.
It takes about 30 seconds to 2 minutes for the fuel savings of turning off the engine to be negated.
An idling car engine uses up to half a gallon of fuel per hour.
When a car starts up and the engine is cold, the engine management software operates in "open-loop" mode, using pre-programmed values to determine how much fuel is needed. This ensures that the car starts reliably and minimizes damage to the engine.
