Does it use more fuel? Does it cause more pollution? What does stop-start have to do with idling and the environment?

Find out by reading our helpful article below.

What is stop-start?

A stop-start system automatically switches off and restarts the engine of your car. The idea is to reduce the amount of time your engine spends idling. Hopefully, it will lead to cleaner roadside air, especially outside of schools.

Stop-start should also see a reduction in your fuel consumption and vehicle emissions, and it’s particularly helpful for vehicles that spend a lot of time at a standstill in heavy traffic.

Why is engine idling so harmful to the environment?

Idling means leaving a vehicle’s engine running while it is stationary.

While this is often because of everyday traffic, there are some instances, such as waiting for children outside of schools and sitting in total gridlock, when idling is not necessary and should be avoided.

Idling increases the volume of exhaust fumes in the air, which contain harmful gasses linked to asthma and other lung diseases.

The Royal College of Physicians estimates that 40,000 deaths in the UK are linked to air pollution, with engine idling as a major contributing factor.

How does stop-start work?

Your car can detect when it has stopped moving. Once your brake pedal is depressed, or on manual cars, your clutch is depressed and the vehicle is out of gear, the engine control unit (ECU) cuts the fuelling and ignition to turn off the engine.

When you go to move off again, your engine is triggered to restart in any one of three ways: releasing the brake pedal, engaging the clutch or pressing on the accelerator. You can then continue with your journey without pressing dashboard buttons or turning a key.

The automatic system can be turned off, usually through a button showing an ‘A’.

Do stop-start engines use more fuel?

Research suggests that stop-start technology can result in a 5% to 7% improvement in fuel economy. This saving may seem small but would certainly add up over the lifecycle of your car. In any case, the data shows that they certainly don’t use more fuel.

Do stop-start systems damage your engine?

The argument that stop-start technology is damaging mostly comes from the fear of a cold engine, your engine must heat up lubricants when it starts. However, the technology doesn’t come into use until your engine has warmed to an operational temperature.

If you’re stuck in traffic for a minute and your engine switches off, the lubricants will not cool down to damaging levels. If you find yourself stationary for a longer period of time, the system is designed to start the engine automatically before lubricant temperatures drop too dramatically.

Another feature that start-stop uses to protect your engine, prevents oil from returning to the oil pan. As a result, engines restart with a significant amount of fluid in the engine chamber.

While most engine parts such as your starter motor, ring gear, cambelt and flywheel have to work more frequently than a vehicle without stop-start, manufacturers ensure longevity and ability to operate more frequently through higher manufacturing specs.

Turbos aren’t affected and the build-up of soot (such as around the exhaust gas recirculation (EGR) valve) is minimised through precise engine management control features.

Further advances, such as dry lubricants on engine bearings and improvements to the durability of engine bearings, mean today’s cars are designed to withstand these frequent engine restarts.

Do stop-start systems wear out your battery?

Many stop-start systems are found on newer cars that have modern, robust batteries with a high capacity. In some cars, a separate battery is used to restart the engine as well.

Cleverest of all, your car’s computer checks charge levels in your battery before attempting to shut it down. If it decides there isn’t enough charge to restart the engine, it’s left running.

Do stop-start engines cause more pollution?

Regardless of how somebody drives there will always be moments when their car is stationary. As a result, a journey using a stop-start engine will give off fewer emissions than the same journey without one.

A  study from the Polytechnic University of Madrid measured the CO2 emissions of two four-wheel-drive vehicles. A reduction of more than 20% was recorded for the car equipped with the stop-start system.

Researchers concluded that despite variability in driving style, grade and type of streets, traffic congestion and engine operating temperature, the car equipped with the stop/start system had a lower CO2 emission factor intrinsically.

Are stop-start engines better for the environment overall?

There’s no doubt that stop-start technology reduces CO2 emissions. The real question is whether the pollution caused by the manufacture of extra parts is offset by reducing emissions over the lifecycle of a vehicle.

Similarly, how much waste is created at the end of a stop-start vehicle’s life?

Unfortunately, there don’t appear to be any studies that address these questions, so for the moment, they remain unanswered.

Hopefully, the popularity of start-stop engines will make idling less of an issue in future.

Adapted from an original article by