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AAA World | Auto
Understanding a Car’s Stop/Start

HOW YOUR CAR’S STOP/START FUNCTION WORKS—AND WHY IT’S BENEFICIAL

Q: My car has an automatic engine stop/start feature. So, when I’m idling at a red light or stopped in traffic, the engine automatically turns off. It then restarts when I take my foot off the brake. Can all of this stopping and restarting be good for the engine? It seems like a lot of unnecessary wear and tear. Also, how much gas does this feature actually save the average driver?
  
At a red light
  
A: Fear not. The drivetrains in vehicles with stop/start systems are upgraded to withstand the demands of this technology. Affected internal engine components have been made more robust to withstand the added strain of frequent starts, and the starting motor is more powerful and designed for significantly more use.

Battery capacity is also increased. Not only does the battery have to restart the car many times in stop-and-go traffic, but it also must power the lights, radio, wipers and climate control blowers while the engine is off. In extreme temperatures, many cars will restart the engine as needed when the vehicle is stopped to keep the climate control system operating and the passengers comfortable.

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In testing done by AAA and others using the EPA’s urban test cycle, cars with stop/start delivered fuel savings of up to 7 to 10 percent, which was enough to save a driver between $262 and $375 a year in a vehicle that gets 20 miles per gallon, goes 15,000 miles a year, and uses fuel that costs $5 a gallon.

It should be noted that many drivers will actually save more money since many real world traffic jams require far more stopping and starting than does the EPA test cycle. The more stops a driver faces, the more fuel the stop/start feature will save. Stop/start also reduces tailpipe emissions, so it has a positive effect on the environment.

Of course, if you really hate stop/start, it can be turned off in most cars.