The Engine Start-Stop Systems Conspiracy

Chances are that if you bought a new car in the last couple of years or so, one of the modern technology features present on it makes your engine shut down everytime you stop for more than 1-2 seconds, sometimes even less.
Engine start-stop button in a BMW 2 Series 1 photo
Photo: Florin Profir
Called “start-stop,” the technology is heralded as the next best thing in the automotive industry since the invention of windshield wipers or rearview mirrors. Some carmakers also call it “micro-hybrid technology” for reasons that I will soon explain.

In theory, there are nothing but upsides to start-stop systems, whether you like them for the lower fuel costs or for the fact that they mildly contribute to fewer emissions inside the city you're living and using them in.

As the official nomenclature suggests, a start-stop system simply shuts off your car's internal combustion engine (ICE) instead of leaving it idle during prolonged stops. It then almost miraculously starts it again the moment you either get your foot off the brake or press the clutch to select the first gear in a vehicle with a manual transmission.

Newer vehicles fitted with the system make the transition from “off” to “on” almost seamless and in a fraction of a second, less time than the blink of an eye.

Since multiple engine starts in a short amount of time would put a lot of stress on conventional starter motors, to the point of destroying them prematurely, cars that have “start-stop” use heavy duty starts, specifically designed for the job at hand.

They also have better batteries, which in certain vehicles can also be charged via regenerative braking, thus making them micro-hybrids. In the overall hybrid cars scheme, micro-hybrids are just below mild-hybrids, and two steps bellow full hybrids.

Some carmakers have resorted to a so-called integrated starter-alternator (ISG), while others only use a heavy-duty starter motor and call it a day. Both versions of a start-stop system work in similar ways and achieve the same thing, though, better fuel economy in stop and go traffic.

All is fine and dandy, especially since the technology is not expensive and has a much lower weight disadvantage compared to what is found under the hood of a full hybrid. But is everything as fantastic as all these carmakers are making it seem?

Modern cars have so many electronics and power consumers that they need a lot of continuous current to keep working, especially when the ICE, the main “distributor of volts to the battery” is shut down. Lights, climate control, audio system, not even the airbags will work if there is no power, which is why in cars with start-stop the battery is put through much higher strain.

You'll probably say “Hey, Alex, stop smoking that, carmakers have thousands of engineers that have already thought about what you're implying!” Sure, I bet they did, but that doesn't take away anything from the fact that each carmaker is essentially a business, and their main agenda is to sell cars, lots of them. This is the 21st century, and nobody's still selling cars that are going to last decades, like in the old days.

Second of all, and a hell of a lot more important, most modern cars have turbocharged engines, also mostly in the name of efficiency, and I hope you all know how hot a turbo can get under load. Older fellows might remember that in every turbocharged car's manual there was an addendum that urged drivers to keep their engines at idle for about a minute after some spirited driving, for the turbo to cool down.

Most newer turbocharged cars use ball bearing turbochargers that are both oil-cooled and water-cooled, so there is less heat soak, and the risk of oil coking is minimal following a hot shutdown of a turbo engine, but it still exists, though. I'm not entirely convinced that a start-stop system on a heavily turbocharged vehicle (think BMW M or Mercedes-AMG) is the best thing to keep it in perfect working order for years and years.

Last, but certainly not least, even if you don't a have a turbocharged ICE under the hood but your car does come with stop-start, there is still a durability problem. A regular engine will probably go through around 50,000 to 100,000 stop-start events in its entire lifetime. One that comes with a stop-start system will probably have almost a million stop-start cycles in the same period.

While an ICE is running, the crankshaft and most of the bearing surfaces don't touch, since they are separated by a very thin oil film, creating lubrication. When the engine stops is where most of the metal surfaces inside the engine actually begin to touch and continue to do so until the engine is restarted again. That small gap of time between engine “off” and engine “on” is when the highest friction takes place, increasing wear and tear immensely.

Is this amount wear and tear better to happen to your engine than those 5 to 10 percent of fuel economy you get in return from a “micro-hybrid”? That's not for me to answer, but I do know that I've turned off about 99% of all stop-start systems that I've encountered when test driving modern cars, and they weren't even mine.
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About the author: Alex Oagana
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Alex handled his first real steering wheel at the age of five (on a field) and started practicing "Scandinavian Flicks" at 14 (on non-public gravel roads). Following his time at the University of Journalism, he landed his first real job at the local franchise of Top Gear magazine a few years before Mircea (Panait). Not long after, Alex entered the New Media realm with the project.
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