Contributing Author: Craig Fitzgerald
According to the United States Department of Energy, Americans waste approximately 6 billion gallons of fuel every year not going anywhere. Personal vehicles alone make up 3 billion gallons of that wasted fuel, idling in traffic. At the current average of $2.85 per gallon, that’s an $8.5 billion economic loss every year. It’s easy enough for you to turn the key off while you’re waiting outside of school for your kid, but constantly turning the key on and off while you’re idling in traffic is a hassle. That’s where auto stop-start technology comes in, and it’s more complicated than you might think.
What is Auto Stop-Start?
In the simplest terms, auto stop-start is a technology that senses when your vehicle stops for a prescribed length of time and shuts the engine off. That seems easy enough, but there’s a lot of technology at work behind the scenes to keep it operating properly, including:
- Special polymers coating the main bearings on the crankshaft to prevent metal-to-metal contact that might ordinarily occur during the starting procedure.
- Absorbent Glass Mat (AGM) or Enhanced Flooded Battery (EFB) technology, which supports an increased number of start cycles, plus provides enhanced power when the engine isn’t turning.
- A reinforced starter, built to handle significantly more start cycles than cars without auto stop-start.
On vehicles with manual transmissions, an auto stop-start system is pretty simple. You step on the clutch to disengage the transmission, and when the vehicle reaches a stop, the engine shuts off. On automatics, it’s a lot more complicated. Think about this: Prior to vehicles with auto stop-start, you couldn’t start a car with an automatic transmission if it was in any gear other than Park or Neutral. With an automatic, the transmission in a vehicle with auto stop-start has an electrically operated transmission pump that keeps the transmission fluid under pressure, and ready to operate, when the engine turns back on.
There are many other components at work making sure auto stop-start is safe and convenient. In Nissans equipped with a Continuously Variable Transmission (CVT), for example, there’s a lock system on the sub-transmission that keeps the vehicle from surging forward when the engine comes back to life. It also keeps the vehicle from rolling backward on a hill.
Why Do We Need Auto Stop-Start?
Auto manufacturers are looking for every single opportunity to increase fuel economy. According to a study by the Society of Automotive Engineers (SAE), auto stop-start can result in a 5.3 percent fuel savings in city driving cycles, and 4.0 percent in highway driving cycles. Over the course of a year, driving 15,000 miles per year in something like a 2021 Dodge Charger with a 3.6-liter V-6, for example, you save approximately $200 per year driving a vehicle with auto stop/start technology.
What are the Disadvantages of Auto Stop-Start?
First off, most of the “disadvantages” are myths. For instance, starters and batteries are no more likely to fail than in a car without this technology, because they’re designed specifically to provide service in such an environment. At some point, your dad probably told you something like “It takes more fuel to start a car than it does to keep it idling.” That may have been true in the era of QuadraJet carburetors, but it hasn’t been true for a long, long time. Idling for just 30 seconds requires more fuel than starting a car with direct injection.
The big disadvantage right now is the sensation of the engine turning on and off a hundred times when you’re stuck in traffic. Some manufacturers do it better than others, but they’re all getting better. In the early days of auto stop-start technology around 2014 or so, the restart in some cars – BMW in particular – could be abrupt and annoying. In 2021, with auto stop-start appearing on about half of the cars and trucks sold in the United States, the feel of a restart has improved dramatically. It’s much smoother and less jarring than it used to be.
How Do I Disable Auto Stop-Start?
Still, though, there are vehicles where the restart procedure is anything but smooth. That’s ok if the engine shuts off and starts again just a few times on the way to work, but in five miles of bumper-to-bumper stop-and-go traffic, it can drive you insane. That’s why more and more manufacturers have listened to owner feedback and included the ability to defeat auto stop-start, at least until you shut the car off yourself.
Every manufacturer we know of that allows you to disable the auto stop-start function does it via a non-latching switch either on the dash or close to the start button. “Non-latching” means that the switch will reset to default mode (e.g., auto stop-start ON) as soon as you turn the car off. The switch is usually labeled with a capital A with an arrow encircling it. Look for this symbol, or read your owner’s manual to learn more.
Craig Fitzgerald began his automotive writing career in 1996, at AutoSite.com, one of the first online resources for car buyers. Over the years, he’s written for the Boston Globe, Forbes, and Hagerty. For seven years, he was the editor at Hemmings Sports & Exotic Car, and today, he’s the automotive editor at Drive magazine. He’s dad to a son and daughter, and plays rude guitar in a garage band in Worcester, Massachusetts.