By on February 22, 2010

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.

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23 Comments on “The Problem With Start-Stop Systems...”

  • avatar

    True; I can’t see ’em being real useful in the northern Midwest or Northeast, or anywhere in the Rockies, in Winter.

    But, well, there’s always the other nine months of the year, and there’s always places like LA and Phoenix and Miami where it’s rarely that cold…

  • avatar

    Yeah it really is quite obvious it wouldn’t work well in the winter but that’s not all year.

    This is very similar to what idling locomotives do, they run all winter but in the summer it’s a great feature. Granted its not for stop and go on a loco… Depending on the model there is a 10-30 minute timer that shuts them down. Kick the reverser into forward or reverse and it will fire up, although that can take up to 5 minutes.

    I guess the point I’m making is that it’s great because the savings will all add up and it doesn’t require any thought on the part of the operator/driver.

  • avatar

    But then in LA and Phoenix, you’re quite likely to need that air conditioner to keep running while you’re sitting at a stop light…

    • 0 avatar

      I live in southeastern PA and the A/C in my Vic runs in some capacity for about eleven out of twelve months of the year. I would require a 100% availability of my car’s HVAC system.

  • avatar
    Gardiner Westbound

    The last thing you want is a diesel cycling on and off in winter temperatures. Diesels take a long, long time to reach operating temperature and supply heat to the cabin in cold weather. They do not produce sufficient interior warmth when idling, none if turned off, a real problem if you’re stuck in bumper-to-bumper traffic. A block heater and heated seats are winter necessities.

    • 0 avatar
      Mirko Reinhardt

      The last thing you want is a diesel cycling on and off in winter temperatures.

      Exactly. My diesel BMW deactivates the start/stop if it’s below 3°C. I don’t see that as a problem, it would be a problem if it didn’t.

  • avatar
    Brian P

    Regarding the A/C, that’s moving towards being electrically operated anyhow. Some are already in production.

    • 0 avatar

      The electric A/C systems are only found in Hyrbids, and use a good bit of power to run. A car with a normal 12V system wouldn’t be able to run it. It would be about the same as running the starter every time you wanted A/C. How long do you think the system could work like that? In a hybrid, the high voltage system has the power to run an electric compressor, but how big is that battery?

  • avatar

    Cold (or warm) starts create more engine wear than high mileage. I prefer to spend the extra penny or two on gas to keep my engine running at stop lights.


    • 0 avatar

      When these systems were being developed, the manufactures were adding secondary electric oil pumps to keep the engine primed. I don’t know if this ever made it into production, but this along with keeping the engine warm, would virtually eliminate the added wear.

    • 0 avatar

      Warm starts are not problematic. Millions of taxi-engines would otherwise die an early death.

  • avatar

    There are some big clarifications that are needed. The fact that they did this test with the diesel engine in the doldrums of winter – now did they also do the test in warmer temperatures? I understand that every systems has drawbacks – but provide a more thorough test. To me it seems this was set up to only show the negative side of this system.

    • 0 avatar

      that test is meaningless, those diesels are so efficient, they even have burners built in to keep the coolant warm enough in winter. and no one claims much improvement outside the city, so why test it there?

      With a gasoline engine that is different, especially the high-hp engines prevailing in the US. and not to pun on the Germans, but the companies that are not able to build a hybrid, probably don’t have the best start-stop mechanism either.

      For real life US applications, it will work better.

      In addition, the makes tested, are known for expensive repairs, so I wouldn’t trust them with such technology int he first place, damn Germans, always making it so complicated and perfect that it doesn’t work.

      the same they said about the hybrids and that they wouldn’t save much fuel in real life and would break. Prius is now in 3rd generation, the most (real life) efficient vehicle and has no failures of starters. Oh, they also have a heat storage and electric AC. See, technology can work when you know how.
      (yes, I know, unintended acceleration… but that is not related)

  • avatar

    These findings will hardly be a revelation to hybrid owners in northern climates. For the very reasons cited, hybrids experience significant increases in fuel consumption during colder weather. The ICE has to keep running long enough to bring the coolant, engine oil and catalytic converter to normal operating temperatures before it will start cycling on and off, allowing the car to operate in EV mode.

    At 0 degrees F and below, the ICE will rarely if ever cycle off, almost completely erasing its fuel economy advantage over a gasoline version. Hybrid owners try to counter this by using engine block heaters and partially blocking radiator air flow with limited success. For the most part you shrug it off and hope for a short winter.

    • 0 avatar

      but you lose fuel economy with non-hybrids as well. It is not hybrid-specific. Maybe hybrid owners notice it more since the car is more efficient to begin with and they watch their mileage and have mileage displays. If the Prius drops from 45 to 37 mpg, this still is better than and equivalent 30 mpg dropping to 25 mpg.

      Actually it becomes more obvious if you did it in l/100 km since the mpg is an inverted number. and a 5 mpg drop at 100 mpg is very very little, but looks the same as a 5 mpg drop for a 20 mpg vehicle.

    • 0 avatar

      I think you may be wrong on the part about the ICE not cycling off in cold weather below 0. It does cycle shorter, but still seems to cycle off from what I have observed. I do see about a 10% drop in fuel mileage in the coldest weather, but still am in the low 50s in the winter time. We don’t see 0 F too often, but plenty of teens. A cell phone pic from winter driving:

    • 0 avatar

      Lectrobyte: I own a hybrid and I live in southern Wisconsin — I know whereof I speak. Furthermore, I belong to a hybrid owners club in which this issue is discussed thoroughly, especially at the start of every winter.

      It is true that gasoline engine cars see an increase in fuel consumption in cold weather but for hybrid owners that increase in consumption isn’t just more noticeable, it is measurably larger.

  • avatar

    My more mundane question has always been how much beefier will you have to make the starter motor (and starter solenoid) to cope with 10 to 100 times more applications over the life of the car compared to a non start/stop vehicle. Will the gas savings make up for the extra cost and weight of a high endurance starter motor? Will I need a larger capacity battery if I am using the start/stop feature frequently? Will the feature cut out if my battery is weak?

    Hypermilers suggest turning the car off if you are going to idle for more than a minute or so, but I always wondered if this is a false economy especially when the bill for a new starter solenoid comes due.

    • 0 avatar


      While one example is hardly representative, I decided to implement a number of tricks with a 2000 Civic coupe EX (5-spd) in Arlington County, VA from late 2003 until selling it in mid-2006.

      Over a 12-month period, replicated city routes routinely yielded about 31.5mpg. Once I began shutting off the engine at lights I knew I’d sit at for more than 10 seconds (ha – most for 2-4 minutes, median), economy improved to about ~34mpg. But it wasn’t just shutting off the engine that brought the greatest fuel savings: it was coasting in gear whenever possible to lights – still retaining control, but seeing the fuel flow deactivate. That was more difficult to do b/c I was most concerned with safety. However, it was attainable (the “NoVA Creep”) especially in spring and fall – to the tune of about another 3.5mpg.

      Adding these tricks, which quickly became automated, to a reasonable amount of highway travel routinely saw us getting 500+ miles/tank (tank=11.9g) anytime we mixed driving (and no, I didn’t engage in any engine shutoffs on I-95 ;). Definitely more work than some folks want to undertake, but I considered it a worthwhile experiment. And, considering the routes I routinely drove, I wasn’t even using the starter as much – a well executed release of the brakes and slip into 2nd or 3rd was always enough to get her moving…

      After an obscene number of miles on the car, no starter, clutch, or battery problems. Again, just one case, though.

  • avatar



    Winter is no excuse for not employing these systems nor for the EPA to not allow their results in EPA Cycle testing!

  • avatar

    “An interesting discovery”?

    Discovery implies fiding something which is hidden. This is not. The manufacturers clearly state that the system is not active in cold weather.

  • avatar
    Tricky Dicky

    ** 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.

  • avatar

    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.

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