Sylvie Willis
The start/stop function in cars improves fuel economy by shutting off the engine when the car is idling, and then restarting it when the brake is released or the accelerator is engaged. The technology has been in use in Europe for years, but its effectiveness in saving fuel has been debated. While some people find the system annoying, tests have shown that the start/stop function can improve fuel economy by between 3% and 26.4%. For example, a BMW 328i GT used 9.5% less fuel with the system on, while a Jaguar F-Type R used 10.9% less fuel.
| Characteristics | Values |
|---|---|
| How does it work? | The automatic start/stop function shuts off the engine when the car is idling and restarts it when the brake is released or the accelerator is engaged. |
| Fuel economy improvements | Depending on driving conditions, improvements range from 7.27% to 26.4% during testing. Some sources state that the range is between 3-12%. |
| Cost savings | The cost savings depend on the fuel economy improvements. For example, an improvement of 1 mpg saves $220 at $2.00 per gallon. |
| Maintenance and engine life | Some sources suggest that any cost savings will be consumed by additional maintenance and a potentially shorter engine life. |
| Emissions | Start-stop systems can prevent pointless emissions by reducing idle time. |
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What You'll Learn
Fuel economy improvements vary between 7.27% and 26.4% depending on driving conditions
Fuel economy improvements from start-stop systems vary depending on driving conditions, with improvements ranging from 7.27% to 26.4%. Start-stop technology automatically shuts off the engine when the car is idling, such as in heavy traffic or at traffic signals, and restarts it when the brake is released or the accelerator is engaged. This reduces idle time and fuel consumption, with potential fuel savings of up to 10-12% according to some estimates.
The wide range in fuel economy improvements is due to the varying driving conditions and idle times experienced by different drivers. For example, a driver who frequently idles in traffic or at long signals will see greater fuel savings with a start-stop system compared to someone who spends most of their time driving on highways or in less congested areas.
In one test of a Mini Cooper, the fuel economy improvement with the start-stop system engaged was found to be 2.9%, increasing from 30.0 to 30.9 mpg. However, when the air conditioning was turned off, the savings increased to 9.5% at 33.2 mpg. This illustrates how driving conditions and other factors can impact the effectiveness of start-stop systems in improving fuel economy.
While start-stop systems can improve fuel economy, there are also concerns about the potential additional maintenance costs and reduced engine life associated with these systems. Some drivers also find the technology annoying or disruptive, particularly if the calibration is not optimal. Despite these drawbacks, start-stop technology can still provide significant fuel savings over time, especially for drivers who frequently encounter idle time during their commutes.
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The longer you sit idle, the more fuel you save
The start-stop function in cars is designed to improve fuel economy by shutting off the engine when the car is idling and restarting it when the brake is released or the accelerator is engaged. This technology can lead to significant fuel savings, especially during city driving with frequent idling.
The amount of fuel saved by using the start-stop function varies depending on driving conditions and the specific vehicle. According to tests conducted by the Society of Automotive Engineers (SAE), the fuel economy improvements ranged from 7.27% to 26.4%. Similarly, tests conducted by Edmunds on a Mini Cooper and a Jaguar showed varying results, with fuel savings ranging from 2.9% to 10.9%.
The engineers interviewed by Edmunds estimated potential fuel savings between 3% and 12%, depending on driving conditions. They emphasized that the longer the car sits idle, the greater the fuel savings. For example, a car that typically achieves 20 miles per gallon (mpg) in the city could see an improvement of 2 to 3 mpg with a start-stop system.
This is supported by research from Argonne National Laboratory, which found that turning off the engine during brief stops as short as 10 seconds can save fuel and reduce emissions. However, it is important to note that turning the engine on and off in heavy stop-and-go traffic is not recommended for safety reasons and may not provide significant fuel savings. Additionally, while idling, the engine takes longer to warm up, and the catalytic converter, which reduces harmful emissions, reaches operating temperature more slowly.
In summary, the start-stop function can lead to notable fuel economy improvements, especially during city driving with frequent and prolonged idle periods. The longer the car sits idle with the engine off, the more fuel savings can be achieved. However, it is important to balance these savings with safety considerations and follow the recommendations of auto manufacturers regarding engine idling.
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Stop-start systems can save up to $220 at $2 per gallon
The start/stop function in vehicles improves fuel economy by shutting off the engine when the car is idling and restarting it when the brake is released or the accelerator is engaged. This technology is designed to maximize fuel economy, and its use depends on driving conditions.
According to a forum post, the start-stop system can save up to $220 at $2 per gallon. The post assumes a fuel efficiency improvement from 30 MPG to 31 MPG, resulting in a savings of $220 over 100,000 miles at $2 per gallon. This calculation considers the potential extra cost of the starter, which may offset the savings.
The actual fuel economy improvements from using the start-stop function can vary. Testing by Edmunds on a BMW 328i GT and a Jaguar F-Type R showed fuel savings ranging from 2.9% to 10.9%, with corresponding increases in fuel economy. The Society of Automotive Engineers (SAE) reported fuel economy improvements of 7.27% and 26.4% for different drive cycles, with the larger improvement associated with more idle time. Engineers estimate potential fuel savings in the range of 3-12%, depending on driving conditions. The longer a vehicle sits idle, the greater the potential savings with a start-stop system.
While start-stop technology can save fuel and money, it also has its drawbacks. Some drivers dislike the lack of control when the engine turns off automatically and the vibration on startup. Additionally, there may be concerns about the durability of certain system components, such as the starter and battery, which may need to be replaced more frequently. Despite these considerations, start-stop systems offer a way to improve fuel efficiency and reduce fuel costs, particularly in urban driving scenarios with frequent idling.
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Restarting an engine takes marginally more fuel than idling
Restarting an engine does take marginally more fuel than idling, but only for a fraction of a second. The starting process takes about half a second, and while it does use more fuel, it is still more fuel-efficient to restart your engine than to let it idle for more than a second. Modern fuel-injection systems have proven to be better for the engine, and overall, more fuel is used when a car is idling compared to stopping and starting your engine.
The idea that idling engines were better came from carburetors, which used a mix of air and fuel for engine performance and needed more fuel when engines started. While idling, maintaining the same amount of fuel was best to save energy. However, fuel-injection systems have become the standard, and it is now more efficient to restart your car. Less fuel is used in the process compared to carburetor systems.
The use of start-stop technology can improve fuel economy by between 3 and 12 percent, depending on driving conditions. The longer you sit at a standstill, the more you save. For example, a 2014 Mini Cooper with the system off consumed 2.7 gallons of fuel, and with the system on, it consumed 2.6 gallons—a modest fuel saving of 2.9 percent. However, when the air conditioning was turned off, savings shot up to 9.5 percent.
According to a 2015 study by the Argonne National Laboratory for the U.S. Department of Energy, continually stopping and starting your car more than 20 times a day could impact the car's battery and starter. However, cars with the restarting system often have overbuilt and oversized motors to address wear concerns.
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Start-stop systems prevent pointless emissions
Start-stop systems are designed to reduce the amount of time a car engine spends idling, thereby reducing fuel consumption and vehicle emissions. The system automatically switches off and restarts the internal combustion engine when the vehicle is at rest, cutting fuel use and eliminating idle emissions. This is particularly helpful for vehicles that spend a lot of time stationary in heavy traffic. Idling increases the amount of exhaust fumes in the air, which contain harmful gases linked to asthma and other lung diseases.
The effects of start-stop systems are not currently included in EPA fuel economy estimates, but they can lead to significant fuel savings. Engineers estimate fuel savings in the range of 3-10%, with some venturing as high as 12%. This wide span accounts for the variety of driving conditions. The longer a car sits idle, the more fuel savings are achieved. For example, a car that manages 20 mpg in the city could earn 22 or 23 mpg with a stop-start system.
In one test, a Mini Cooper with the stop-start system engaged used 2.6 gallons of fuel, compared to 2.7 gallons with the system off, a modest fuel saving of 2.9%. However, when the air conditioning was turned off, fuel savings shot up to 9.5%, with fuel economy climbing from 30.0 to 33.2 mpg. In another test, a BMW 328i GT used 3.1 gallons with the system off and 2.8 gallons with it on, a savings of 9.5%.
Start-stop technology is becoming increasingly common, with approximately 65% of passenger cars in 2022 featuring the technology, up from only 9% in 2016. This growth is driven in part by stringent regulations mandating the improvement of vehicle fuel economy and the pursuit of low-emission fleets to meet ambitious national carbon-reduction targets. Start-stop systems are particularly useful for reducing emissions while the transition to fully electric vehicles is ongoing.
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Frequently asked questions
The increase in fuel economy from using start-stop technology depends on driving conditions and varies between 3-10% or even as high as 12%, according to engineers. A study by the Society of Automotive Engineers found that using start-stop can see a car's fuel economy improve by over eight percent in heavy traffic. Some tests have shown improvements of 9.5% and 10.9% in fuel economy. Other tests have shown improvements of 7.27% and 26.4%.
Start-stop technology shuts off the engine when your car is idling and restarts it when the brake is released or the accelerator is engaged.
Start-stop technology improves fuel economy and reduces idle time.
Some people find start-stop technology annoying because it can cause a slight pause when restarting the engine. There is also the potential for increased maintenance costs and a shorter engine life.
You can leave the feature engaged and try to get used to it by learning the "trigger point", which will allow you to decide when you want to engage the feature at a stop and when to bypass it.
