The Problem With Start-Stop Systems

Edward Niedermeyer
by Edward Niedermeyer

For an industry under ever-increasing pressure from government emissions standards, start-stop technology (which shuts off engines under idling conditions) seems like an easy route to improved fuel efficiency. Cheaper and less complicated than a true hybrid system, a number of automakers from BMW to Kia are proliferating start-stop technology across their product lines without hybrid-like price premium. Since this technology represents a relatively easy, incremental efficiency upgrade, we’ve wondered why it hasn’t been made available stateside, where hybrids are making up a growing proportion of sales. Detroit’s executives seem to think it’s a good idea, and Mazda has even gone so far as to complain that EPA test results refusing to show the Japanese test-cycle’s 7-9 percent improvement is the main factor preventing it from bringing more stop-start equipped vehicles to the US. But there’s another issue preventing stop-start from becoming standard issue industry-wide, and it’s actually remarkably obvious.



In its latest print edition, German car mag Auto Motor und Sport performed a 200km real-world winter efficiency test on six German-market, entry-level diesel station wagons (A4, Passat, Mondeo, Insignia, C-class, 3-series), and it made an interesting discovery. Though the VW, Audi and BMW were equipped were equipped with stop-start systems, the near-freezing temperatures and freeway/country road course meant that the Audi and VW systems only rarely activated (nur in wenigen Einzelfällen), and the BMW didn’t do the stop-start thing even once. Although a more urban course might have seen the system activate a bit more often, Auto Motor und Sport rightly concludes that temperature plays an important role in the efficacy of stop-start systems. After all, engines run far less efficiently when cold, so if deactivating the engine in near-freezing conditions can cause it to dip out of its optimum operating temperature, stop-start could be a a recipe for worse efficiency.

Of course, the start-stop systems have smarter computers than that, which is why the systems rarely activated in AM und S’s test. And ironically, the three vehicles equipped with the system actually logged the top CO2 emission results in the test despite the recalcitrance of their technological advantages. Still, just as cold-weather performance remains a huge question mark in the development of electric vehicles, living in a cold climate could seriously limit the advantages of this seemingly inevitable efficiency-boosting gizmo.

Edward Niedermeyer
Edward Niedermeyer

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  • Tricky Dicky Tricky Dicky on Feb 24, 2010

    ** BREAKING NEWS ** Automobiles have higher energy requirements when it's cold outside. Shocking stuff. You sit in a traffic jam on a warm day and then try and make an argument that S&S doesn't make sense. Easy to use, easy to implement, good sense all round. As a design objective: - make a vehicle use as high a proportion as possible of the fuel consumed to create forward motion - ...you'd have built S&S in from the beginning.

  • Dissappointed Dissappointed on Feb 14, 2014

    Regarding Start & Stop systems: I'm not sure if this is related to S-S technology but since it involves the first vehicle I purchased having this system I have my suspicions. It's either just a battery/electrical system issue or it's related to the battery/electrical system in support of S-S. I purchased a 2013 BMW model X3 SUV in Aug. 2012. The S-S system works fine (instant, effortless, & quiet) but I've had some major battery discharging problems beginning in Oct. 2013. I was quite puzzled considering how much the vehicle cost and the fact that it was only a little over a year old. I charged the battery back up to 100%. Then in Dec. another low battery warning. Another re-charge. Another warning in Jan. By this time I'm getting pretty frustrated that I've had to re-charge the battery three times in four months. I scheduled an appointment with the dealership service dep't. They had to replace the battery, battery cable, and battery sensory cable. Wanting to find out what this was all about I contacted four different people: The salesman, a service tech, the service dep't. manager, and the BMW North American Customer Service Dep't. rep. It was obvious at the onset that they weren't open to any discussion dealing with the issue. When I first inquired I got the impression that none of them knew what the problem was (or maybe just didn't want to talk about it). Initially I got varying responses ranging from the too much computer technology for the electrical system to support to it being related to cold weather. After pressuring them further they finally stated that it was an inherent problem with BMW vehicles in colder states. It's bad enough that I have to suffer with sub zero temps here in Minnesota - now I'm being penalized with the vehicle I drive (lol). But the real kicker was when I went to pick up the vehicle. The service manager told me that I should get a battery charger and expect to have to re-charge the battery every once in awhile. Also that if the warning light came on while out driving, I should make sure and drive for a least a couple of hours so the alternator could re-charge the battery (just when I thought I was going to save money on a fuel efficient vehicle). I responded by telling him that if the salesman had been honest and told me of this issue I probably wouldn't have purchased a vehicle with S-S technology. During my discussion with the national customer service (now there's a contradiction of terms) rep I inquired if BMW would be willing to re-purchase. I was told that for this to happen the dealership service dep't. would have to declare that it was a defective vehicle. I guess I can expect that to happen when it gets really hot here in Minnesota in January. I'm not as upset with the engineering flaw on the part of BMW as I am with the way their staff handled it.

  • Wjtinfwb Funny. When EV's were bursting onto the scene; Tesla's, Volt's, Leaf's pure EV was all the rage and Hybrids were derided because they still used a gas engine to make them, ahem; usable. Even Volt's were later derided when it was revealed that the Volt's gas engine was actually connected to the wheels, not just a generator. Now, Hybrids are warmly welcomed into the Electric fraternity by virtue of being "electrified". If a change in definition is what it takes, I'm all for it. Hybrid's make so much sense in most American's usage patterns and if needed you can drive one cross-country essentially non-stop. Glad to see Hybrid's getting the love.
  • 3-On-The-Tree We also had a 1973 IH Scout that we rebuilt the engine in and it had dual glass packs, real loud. I miss those days.
  • 3-On-The-Tree Jeff thanks. Back in 1990 we had a 1964 Dodge D100 with a slant six with a 3 on the tree. I taught myself how to drive a standard in that truck. It was my one of many journeys into Mopar land. Had a 1973 Plymouth duster with a slant six and a 1974 Dodge Dart Custom with 318 V8. Great cars and easy to work on.
  • Akear What is GM good at?You led Mary............................................What a disgrace!
  • Randy in rocklin I have a 87 bot new with 200k miles and 3 head gasket jobs and bot another 87 turbo 5 speed with 70k miles and new head gaskets. They cost around 4k to do these days.
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