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.