Are Stop-Start Engines More Efficient?

Stop-start technology systems are an increasingly common feature of cars, and they are marketed as fuel and emissions-saving. But does the science stack up?

Fuel economy might be high on your list of priorities when you’re looking for a new car, and with this in mind, you may be wondering whether to choose a vehicle that features automatic stop-start technology.

Keep reading to find out how stop-start engines work, and whether they could help you to lower your driving costs and reduce your emissions.

How does stop-start technology work?

Featured in most modern cars, start-stop technology does exactly what the name suggests; here’s how it works:

1. A stop-start system cuts the engine when a vehicle is stationary.
2. It then restarts it when the brake is released, the clutch is engaged, or the accelerator is pressed.
3. The technology relies on an engine control unit to detect when the car is motionless or when it’s out of gear.
4. In these situations, the fuel supply and spark to the engine are halted.
5. This process happens automatically, but if you have a car with one of these systems, you can choose to disable it. This is usually done by pressing a button displaying an ‘A’.

By switching the engine off automatically when you’ve stopped, for example, when you’re waiting at traffic lights, junctions or in heavy traffic, the systems are designed to reduce the amount of fuel burned and make vehicles more environmentally friendly.

When was start-stop technology invented?

Start-stop technology is by no means new. Volkswagen introduced its first car featuring start-stop technology back in 1991. But, with modern car buyers looking for ways to reduce their carbon footprint, the technology has become much more popular in recent years, with most manufacturers introducing models featuring the technology.

How do start-stop batteries differ from regular batteries?

If start-stop systems turn the engine off when your vehicle is stationary, how is it that your ancillary systems (like air con or lights) continue to operate? The answer lies in the battery that powers the start-stop system:

• Unlike a regular battery, a start-stop battery is not simply a starter battery, designed to supply a large current to turn the starter motor. It’s also a ‘cyclic’ battery with the ability to be discharged and recharged many times.
• Many cars also have brake regeneration, so any energy created when the brakes are applied is also stored in the battery for later use.
• Most vehicles need to come to a complete stop for this system to work, but others disconnect the power to the engine every time the brakes are applied and use the stored power to maintain the lights and other systems. As soon as you apply the accelerator, the battery restarts the petrol engine.

What happens if you put a normal battery in a stop-start car?

Applications with this technology require a battery that is compatible and able to cover these robust functions. If a standard battery is fitted, it will fail prematurely; these batteries should still be checked regularly to ensure that they are in good working order.

At Kwik Fit, our fully-trained technicians can carry out a free and thorough check of your start-stop battery using the latest testing equipment. Find your nearest Kwik-Fit centre and get your start-stop battery checked today.

Free battery health check

What are the disadvantages of start-stop technology?

There are a handful of potential downsides that come with start-stop technology, including: 

• Component wear - The repetitive stopping and restarting mean that the starter motor, engine, and battery have to work harder than usual, which can lead to premature wear.
• Expensive parts replacement - The batteries and components used in a start-stop system are more sophisticated, and therefore more expensive to replace when things go wrong.
• Driver discomfort - Occasionally, drivers find the slightly delayed start or the vibrations distracting or uncomfortable compared to controlling the engine themselves.
• Trust issues - Many drivers feel wary about the engine cutting out on it’s own, preferring to control the vehicle themselves.

Does start-stop technology save fuel?

Start-stop technology does save you fuel by reducing engine idling and the unnecessary fuel consumption that goes with it. By shutting off the engine whenever it isn’t actively needed, fuel consumption levels are reduced over time. Recent studies have shown that auto start-stop technology can save up to 15-20% of fuel in certain conditions.

How stop-start technology reduces emissions

It’s not just the benefits to your wallet that you should think about when deciding whether to use stop-start technology; there are also environmental benefits to consider. 

Cutting emission in slow-moving traffic

Start-stop technology also lowers emissions. A recent scientific study examined the influence of the start-stop tech on the emissions of a four-wheel-drive diesel vehicle and found that emissions were reduced by 20% in urban traffic (at an average speed of just under 10mph).

The emissions-lowering capability of stop-start systems is particularly important in towns and cities, where traffic is likely to be stationary for longer.

How else can you drive more efficiently?

Stop-start vehicle technology can play an important role in making your car cheaper to run and less polluting, but there are other ways to improve efficiency too.

1. Change your habits behind the wheel

The way you drive can have a surprisingly significant effect on how much fuel you burn. Harsh accelerating, for instance, can push up your fuel bill, as can driving quickly. Travelling at 70mph uses nearly 10 per cent more fuel on average than driving at 60mph. 

It’s a good idea to think about how you use air conditioning in your car, too. This system causes your vehicle to burn more fuel, so when travelling at lower speeds, it’s generally recommended to switch it off and open your windows instead to keep the temperature down.

2. Lose unnecessary baggage

The heavier your vehicle is, the more fuel it will use. So, remove any items you don’t need before setting off on journeys. If you have a roof rack, think about taking it off when it’s empty too. This container might be a handy way to increase your storage capacity, but it also increases drag, making your car less efficient.

3. Choose your routes wisely

Before setting off on a new route, do some research into the best way to get to your destination. There might be a more direct route available than the one you initially think of. If possible, choose your travelling time wisely too. For example, if you can avoid travelling through congested areas at rush hour, do so.

4. Book regular services

Keeping your car in good condition is essential when it comes to maximising efficiency - and this is where regular servicing comes in. As well as helping to ensure that any problems are picked up early and are therefore easier and cheaper to fix, frequent servicing will mean your car will run as smoothly as possible. For example, regular oil changes and filter replacements, which are included as standard during vehicle services, will help to maximise fuel efficiency.

Drive smoother with Kwik Fit

Book your vehicle in for a free vehicle safety check at your local Kwik Fit for peace of mind and a smoother ride.

If you’ve got any concerns about your engine or other critical car components like brakes, battery, or tyres, contact us today, and we’ll diagnose the problem and get the issues fixed.