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Start-Stop Fuel Savings Test - 2014 BMW 328i xDrive Gran Turismo Long-Term Road Test
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Start-Stop Fuel Savings Test - 2014 BMW 328i xDrive Gran Turismo Long-Term Road Test
Start-stops systems like the one in our 2014 BMW 328i Grand Turismo have the office talking, but how much fuel can they really save?
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I must say, I am surprised! Almost 10 percent improvement from such a small piece of technology. My only question regards the longevity of the equipment. It seems counterproductive for a vehicle to shut off the engine while in gear.. Thanks for doing a practical, real-world test!
Great test - thanks for the solid journalism.
I've got a brand new 328 (400 miles so far) and have been wondering about this. During testdrives the start/stop was disconcerting but already after 2 weeks of ownership, it's no longer noticeable.
Don't forget the added benefits of no engine noise or vibration while waiting at a stop.
What mode were you in? eco, comfort, sport or sport plus?
I had this feature disabled on my 2013 320i. I hated trying to drop the kids off at school only to have the car stop and restart several times just trying to get through the line. The dealership said they lots of disables of this feature so I'm not the only hater.
While the auto start/stop may result in increased fuel savings, what about extra wear on the engine and related components from the more frequent engine starts? (e.g. starter, battery etc).
I tried the system on my 2014 F56 MINI Cooper for three weeks (presumably the same system used here), but had to turn it off. Why? Because on 7 occasions, it shut down the engine completely, just as I needed to pull away (e.g. at stop light or stop sign), resulting in embarrassment (best case) and/or danger (worse case). It did not shut down the engine -- it shut OFF the engine! I had to quickly hit the start toggle.
It's got flawed software. I'm awaiting a fix from MINI (reportedly coming in December. Until then, the system stays off! My MINI is a manual transmission, but this was not a case of me stalling. I have had zero recurrences since auto start-stop has been switched off. Also, the system is occasionally abrupt, and often restarts during full stops to maintain the auto A/C (this is normal behavior, however).
Really appreciate this real-world test. Previous estimates I've seen are that start-stop delivers a 1 mpg benefit, so your result is a little surprising. But then, you did test it under ideal conditions: three hours of city traffic with good driving habits and no A/C. Could you try it starting in the afternoon instead of 7:45am?
Comfort, the default mode.
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Yes, and that's a huge difference in this car. There is quite a bit of idle vibration when the engine runs, more than average, I would say. Certainly more than customer complaint level at a company I used to work for, but then they catered to folks who hated noise and vibration.
Twitter: @Edmunds_Test
The duty cycle (aka general beefiness) of the starter, alternator and battery have been increased to suit this application. And I don't think there's any engine wear issue. Idling isn't a necessarily a picnic for durability, when it comes down to it.
Twitter: @Edmunds_Test
Yes, I plan on tweaking the variables and conditions to see how much the result can vary. This particular test leans slightly toward the best-case side because I wanted to make sure the effect would be big enough to observe and measure. I wanted to know what was reasonably possible. I got more than I bargained for, which is great because even if my eventual "average condition" test comes in a bit lower, there's still reason to expect a benefit worth taking advantage of, especially if a new owner can get used to the system in a couple of weeks like @stevej2001.
Besides, the technology can only improve as it becomes more widely implemented. It won't be long before development shrinks the shortcomings to insignificance. You can bet we'll be keeping tabs on the new systems as they begin to permeate our long-term test fleet.
Twitter: @Edmunds_Test
I said the same issue darex reports while driving a Renault Clio in France. 2-3 times I came to a stop only to (try to) move again right away and the engine died. There I was stuck in traffic with a dead car -- not fun.
The Clio had a manual transmission, maybe it makes a difference? It seemed I was getting off the clutch faster than the start/stop system could react.
Thanks Dan and other commentors who discussed the use of AC with the system, I wondered how that work (though not enough to google it on my own)
Great test, great article, great discussion!
Other scenarios where this will be bothersome/not help economy much: toll booth lines, parking garage lines, parking areas at large events, stop sign-controlled intersections, stoplight-controlled intersections where you're making a right on red - in other words, anyplace you're expected to keep creeping forward. Also not sure I want the engine to keep shutting down in low-traction situations...like a snow-covered intersection on any sort of incline.
For people who face constant stop-and-go traffic (not me, thank god), this can help save gas, although not that much money, since I'm sure the increased "general beefiness of the starter, alternator and battery" is being factored into the price you pay for the car.
There IS an engine wear issue, but automanufacturers have adjusted to suit. The big example are journal bearings for the crank and connecting rod big ends, which due to the start/stop cycle is more prone to damage. This is why you're starting to see coated bearings (irox bearings) starting to be used. Don't know what BMW is doing in their test regime for this.
For manual transmission cars I've driven, it only shuts off engine when you're off the clutch pedal and in neutral. So I step into it and the car starts.
Wow. A fuel measurement of gallons per 100 miles... this is the first time I've seen fuel mileage displayed using a similar format to the (now standard) metric fuel consumption measurement of liters/100km. Interesting.
In Canada, we've been using the 'metric standard' for fuel measurement for years, but using a funky measurement of gallons/100 miles? Does everyone understand the significance of the resulting number? (i.e. that the number of gallons has to be LOWER to reflect better mileage, rather than a HIGHER number (better) when describing miles/gallon.) It's not intuitive and can be confusing to the uninitiated.
So is Edmunds going to push for this method to become a new US standard? It might be easier to simply convert to full-blown metric measurement. Again, interesting.
In this car, once you creep forward the system is deactivated for some period of time. That period of time seems to be the remaining duration of the red light, so the slow creep at a backed-up stop sign, right turn on red or similar should NOT trigger repeated engine stops at each pause. I think the car has to reach a speed identifiable to the computer as clearing the intersection before it can reset and ready itself to do the start/stop trick at the next halt in traffic.
This is the kind of behavior that can vary with software tuning and performance traits such as these will ultimately distinguish a system that's easy to live with from one that's just plain annoying. In these early days different manufacturers are probably going to make different decisions in response to various real-world scenarios like these until some sort of best practice is determined.
Twitter: @Edmunds_Test
We're not in the business of pushing for any sort of standard. We test the cars that come to market and try to sort out good from bad. If a new feature has a benefit that outweighs its drawbacks or cost, we'll most likely point it out and applaud it. As for start/stop, we're still trying to quantify the customer benefit. With this test we've gotten as far as concluding that it's not just smoke and mirrors. There seems to be a tangible benefit that makes it worthwhile to leave it on and make peace with it -- at least in this car.
The automakers are all rushing headlong in this direction on their own because of already-legislated CO2 reduction standards in Europe and CAFE-mandated mpg improvements (CO2 reductions, really) in the USA. This particular fuel-saving method isn't specifically mandated -- government is primarily interested in what does (or does not) come out of the tailpipe. The automakers see this as a step that's relatively easy to take, and they're especially keen on it because it doesn't impact the performance of the car once it's underway.
Twitter: @Edmunds_Test
Yes, that's the theory, and that's my practice. I don't linger with my foot on the clutch, while in gear, except perhaps at a stop sign in an empty intersection. The problem occurs, as I described, when it's time to start moving, I shift from neutral to first (so my foot has touched the clutch), and instead of the engine speed returning to idle (e.g. 1000 rpm), it instead shuts off (not "down", as when the start-stop is engaged), forcing the need for the engine start switch to be engaged. It essentially stalls, rather than revs-up, and this NEVER happens when the start-stop system is off. It's as if, as described by Miata52, the start-stop system and the driver are working at cross purposes. It's a disaster waiting to happen (it's dangerous!). I am confident that BMW will make a successful software solution for this, but until then, experimentation time is over! It's an awful feeling when you say "go", and your car says "no."> @duck87 said:
@duck87 Yes. I meant to say there's no engine wear issue with cars that are built with start/stop from the get-go because of the reasons you state. I'm sure you'd agree that folks should not use their key to manually invoke start/stop at every signal on their older cars without the feature because the engine wasn't designed with that sort of usage pattern in mind.
Twitter: @Edmunds_Test
The manual for our 2014 320i xDrive specifically states that premature wear of some engine components will occur with utilization of the available start/stop feature.
Virtually all hybrids have stop-starts, and their engines generally last better than the engines in conventional gas-only systems.