Skip to main content

There are several tips and tricks available to help you improve your fuel economy. And one of them is increasingly being built right into your car. Many new vehicles have a start-stop system, nominally to reduce how much gas is wasted during idling. But does this feature truly save you fuel? And even if it does, are there any long-term issues that can develop because of it?

How does the start-stop system in your car work?

A close-up of the steering wheel, start button, and start-stop system defeat button in a 2021 Mercedes-AMG GLB 35
2021 Mercedes-AMG GLB 35 start-stop system deactivation button close-up | Matthew Skwarczek

First introduced in the 1970s, start-stop systems, or ‘auto start-stop’ as they’re sometimes called, have become more prevalent in the last few years. And that’s thanks to improvements in automotive electronics, especially in starter motors and hybrid powertrains.

Although each start-stop system is slightly different, they work in roughly the same way. When your car detects you’ve come to a stop and have the brake pedal pressed, it sends a signal to the ECU, Haynes explains. The ECU then cuts your car’s fueling and ignition systems temporarily, shutting the engine down. And when you take your foot off the brake pedal and/or press the accelerator, the ECU tells the engine to restart. It’s even possible to give cars with manual transmissions start-stop systems, CJ Pony Parts notes.

While the latest start-stop systems are fairly smooth, some owners have found them too rough or annoying to use daily. However, automakers have taken several steps to rectify this.

For one, cars with start-stop systems usually have a dedicated button to turn the feature off, Car and Driver notes. And because hybrids’ starter motors often double as generators, they can ‘smooth over’ any lingering coarseness.

Does using the start-stop system damage the engine or other parts of your car?

The black center console of a 2021 Buick Envision with the start-stop system deactivation button in the corner
2021 Buick Envision center console close-up with start-stop system deactivation button in the corner | Buick

But as sophisticated as stop-start systems are, they’re not infallible. And, more to the point, using them means your car’s engine turns off and on multiple times per trip. That’s led to some consumer concern that the technology might be accelerating engine wear and potentially causing long-term damage.

To be fair, shutting off your engine does leave various metal surfaces touching without the lubricating protection of oil. Plus, starter motors do eventually wear out, as do the batteries powering them. So, on a surface level, there is some logic behind the aversion to stop-start tech.

However, for the most part, these potential flaws have been addressed, RAC explains. Firstly, modern oils have significantly better lubricating and wear-protection properties than their predecessors. Furthermore, many stop-start systems don’t turn on until the engine has warmed up. This makes sure the oil and other fluids have properly circulated and coated the various engine components.

Secondly, cars with start-stop systems, hybrid or not, have oversized and overbuilt starters specifically to address wear-and-tear concerns. They can also detect if the battery has too low of a charge to sufficiently restart the engine. If that happens, the engine stays running to recharge the battery.

The stop-start system also knows if your A/C is running, Haynes points out. If it is, the engine stays running to keep it on. And it’s the same story if your heater is running, CJ Pony Parts adds.

Does it actually save you fuel?


Is Remotely Starting Your Car Illegal in Your State?

But, while start-stop systems aren’t necessarily damaging your engine, are they truly improving fuel economy? In a word, yes. But as with any fuel-saving tech, how much you save depends on how and where you drive.

As mentioned earlier, your engine won’t turn off if the HVAC system is running. And that cuts down on the potential fuel savings. When Edmunds tested the start-stop system in a Mini Cooper, reviewers found running the A/C meant ‘only a 2.9% improvement in fuel economy. But with it turned off, the start-stop improved fuel economy by 9.5%. And the Jaguar and BMW tested alongside the Mini also cut their fuel use by roughly 10% using start-stop tech.

In short, stop-start systems can help you save fuel, and they won’t damage your engine. So, unless you can’t stand the restarts, it’s worth keeping it on.

Follow more updates from MotorBiscuit on our Facebook page.