A push-button start in a modern car. Here's the full lowdown on stop-start systems.

Stop-Start Technology — Pros and Cons

Stop-start technology (SST), also known as stop-start engine, auto stop-start, idle-stop or anything similar, is a feature many associate with hybrid vehicles. The key to hybrid vehicle efficiency is that it takes advantage of the opposing strengths and weaknesses of internal combustion engines (ICE) and electric motor-generators. At a stop, unless the hybrid battery needs charging, SST cuts the engine, leaving the battery pack to power lights, the radio and the air conditioning system. Vehicles with SST are sometimes referred to as mild hybrid vehicles for this reason.

One might think SST somehow seeped over to conventional vehicles, but the designers of hybrids didn’t invent stop-start technology. In fact, it was first introduced years ago, at the 1983 Frankfurt International Auto Show.

What Is Stop-Start Technology?

The ICE is a wasteful machine, converting little chemical energy to motion. Despite technological advancements in the last century, there are plenty of ways to improve the ICE. Engines are least efficient when the vehicle is stopped, as the entire motor operates to run the alternator and power the car’s electrical system. The question then becomes, “Why can’t the battery do that on its own?”

With enough battery capacity, there’s no reason to waste fuel as the engine sits idling. SST cuts the motor when the vehicle is stopped, restarting it when it needs to move again, usually triggered by the brake, the clutch or the accelerator pedal. Early SST engines were a bit clunky, but some modern ones start within 0.035 seconds, about a third of the time it takes to blink your eyes.

Pros And Cons Of Stop-Start Technology

Start-Stop Technology limits wasteful fuel consumption and unhealthy emissions.The obvious advantage of SST is the engine doesn’t burn fuel when the vehicle is stationary. This improves fuel economy in stop-and-go traffic situations, where it’s at its worst. In hot weather, though, these improvements are smaller, as SST might cancel to engage the AC compressor. Still, every bit of fuel consumption adds up, whether its 2 percent or 10 percent.

Since SST engines start more often, premature wear might be a concern. Therefore, “adding” it might be a bad idea on a vehicle that wasn’t designed for it. To handle the specific demands of SST, automakers have redesigned engines, starters and electrical systems.

  • The electrical system is usually beefed up with high-capacity batteries, and some carry dedicated starter batteries or supercapacitors. This keeps vehicle systems running, saving energy to engage the engine on demand.
  • Some SST engines feature more-powerful and more-efficient starter motors, or hybrid-like motor-generators, recovering energy for fast and efficient engine starts.
  • A number of SST engines have auxiliary engine coolant, engine oil and transmission pumps to maintain pressure and temperature. New crankshaft bearings prevent premature wear. Regular oil changes with quality oil are especially important for SST engines.

The worst thing about stop-start technology might be all in your head. For drivers that are accustomed to hearing their engine running and feeling the forward creep in vehicles with automatic transmission, having the motor shut off can be unsettling. Once you get used to it, simply enjoy the benefits of refueling just a little less often.

Check out all the electrical system products on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on stop-start technology, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

about author

Benjamin Jerew

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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