Engine start-stop systems not so advantageous
Last month I was asked to choose which feature in a modern car annoys me the most. Because I could — unfortunately — pick only one, I chose the infernal keyless entry system, that supposed modernization whose main effect seems to be the constant misplacement of every automotive key fob I come in contact with.
Truth be told, though, I find the modern idle stop-start function much more of a nuisance. Better, for me at least, is the constant, but mild, thrum of an internal combustion engine at idle than the intermittent silence, not to mention the abrupt wake-up of an engine that can’t decide if it’s awake or asleep.
Only mildly infuriating in a fourcylinder car, it’s seriously irksome when a big V8 or a heavy-piston turbodiesel has to rumble to life at every stop sign. The only reason I didn’t choose it as my No. 1 annoyance is because, unlike keyless entry, you can always shut the bloody thing off.
Manufacturers, of course, claim such high-tech wizardry is necessary to meet increasingly stringent fuel-economy regulations. Stopstart is just one of myriad detailed technologies — more efficient air conditioning systems, radiator shutters and other aerodynamic aids, etc. — being introduced in the quest to meet the United States’ mandate for a 54.5-mile-per-U.S.-gallon fleet average by 2025.
But does it work? More importantly, will you see any benefit?
The answer, like almost everything about fuel economy, is complicated.
I tried to replicate typical city driving while testing Audi’s brandspanking-new 2016 A6 with the stop-start function turned on and off. As unscientific as my little experiment was, I achieved an increase in fuel economy of about six per cent — 9.6 litres per 100 kilometres with the system on, and 10.2 L/100 km with it off — by having the engine stop at every stop sign/stoplight/railway crossing I encountered. So, it works. And because my tester was an already fairly frugal 3.0-litre turbodiesel, chances are gasoline engines, especially of the larger variety, will save even more.
Edmunds.com, testing a supercharged Jaguar F-Type R, recorded a 10 per cent increase. That seems pretty darned impressive. Until you start doing the math. Let’s assume your car, a typical four-cylinder gas-engine family sedan, averages 10 L/100 km in the city. Let’s further assume you’ll save a real-world five per cent with an idle stop-start system by having the engine diligently extinguish itself when the vehicle is stopped. Plug all the numbers — $1.20 a litre for regular unleaded, 7,500 urban kilometres a year, etc. — into your handy-dandy smartphone app and it turns out you’ll save … about $45 a year.
Ouch! Not very much, eh? The number seems even less impressive when you consider that to incorporate stop-start technology into the modern automobile requires a heavier-duty starter and battery (because of its vastly increased cycling), and sometimes even a second oil pump (so oil pressure builds more quickly to prevent engine and transmission damage).
Now, unless you believe automakers have suddenly become altruistic and are absorbing the cost of all this added technology, there’s a price to be paid for this beefing-up of the engine. Factoring in an upfront cost of even $300 — a figure on the low end of the upgrades by most estimates — that’s at least a six-year payback. That’s an extraordinarily long time to put up with something that can be — if you’re as sensitive as I am — a serious annoyance.
So, you might be wondering, why bother?
Well, the real motivation is found deep inside the 1,500 pages of the new U.S. Corporate Average Fuel Economy standards. It turns out that, to encourage the automakers to think frugally, the regulations allow for something called “off-cycle technology credits.” These credits are essentially a reward for incorporating gadgets for which the government testers can’t measure any discernible benefit in its laboratory testing, but thinks will be of benefit to fuel economy anyway.
There’s a raft of such doodads — idle stop-start, various aerodynamic aids and even high-efficiency headlights are included — that earn automakers credits, regardless of their benefit.
In the case of stop-start, it’s an automatic gain of two grams per mile of CO2 reduction for cars, while trucks — ever advantaged by the American government — get a credit for as much as 4.4 g/mile. Throw the entire suite of accredited gadgets at a car and the benefit can be as much as 17.8 g/mile (for non-hybrid trucks), roughly equivalent to two to three miles per U.S. gallon.
For an industry struggling to meet that ambitious 54.5-mpg figure, it’s a freebie few automakers can turn down, even if they know the benefit to consumers is questionable.
And idle stop-start is hardly the only supposedly gas-saving technology that benefit manufacturers more than consumers.
I recently tested Ford’s muchballyhooed 1.0-L three-cylinder EcoBoost engine that powers the 2015 Focus SE. I then compared it with the plain Jane, naturally aspirated 2.0-L four that powers the hatchback version of Ford’s compact. Surprise, surprise — at every highway speed tested, the 2.0-L engine consumed less gas than the supposedly parsimonious 1.0 L. Oh sure, the 2.0-L engine’s advantage was but 0.2 L/100 km, but that’s made more impressive when you consider Ford charges a whopping $1,600 extra for the 1.0-L engine’s privilege of sucking back more gas and losing 35 horsepower.
Even in the city, where you might think those little pistons would regain their advantage (indeed, Ford rates the smaller engine at 8.1 L/100 km in city driving, versus 8.9 for the larger engine), the 2.0 L often eked out another 0.2 L/100 km advantage. And yes, just so you know, the teeny, tiny EcoBoost engine was even equipped with idle stop-start, while the 2.0 L, being Ford’s bargain-basement powertrain, was not.
What is most interesting is how this high-tech gadgetry compares with more conventional fuel-economy savings techniques, shortcuts that savvy consumers have employed for years. Thanks to some way-nifty “efficiency program” software buried deep in my Audi’s tripmeter, I was able to determine exactly how much extra fuel I was using with the car’s air conditioning system, the seat heaters and even the seat ventilators that came with my fully loaded A6 tester.
For instance, I know that the A6’s driver’s seat warmer, set to its highest position, consumes less than 0.1 litres of gasoline per hour (no, not L/100 km) — a mere pittance. Calling for maximum heat, on the other hand, will suck back a more serious 0.5 L/hr; maximum cooling, much to my surprise, consumes a little less.
Again, factor in all those numbers (6.0 L/100 km for the A6 on the highway at 100 km/h), and getting max heat from your vents on a cold February morning might reduce fuel economy by as much as eight per cent. Conversely, forego the ventilation system and just heat up the seats and the steering wheel, and you’ll be wasting less than two per cent. No wonder then, that EV makers — even more desperate for range than conventional automakers are for fuel economy — recommend owners use their seat heaters rather than the heating/cooling system.