I’ve driven Subarus for two decades, and I’ve never heard of this. Between 65% and 80% of the cars sold in the US have this feature and there’s no rush to replace batteries at 8 months.
I recall seeing this same test. It’s worth noting it was done with a normal car that was not designed for auto stop. I’m sure on one designed to do it the break even point is less than 7 seconds.
There is also 7 seconds of wear on those things during idling. If a car is idling at 800 RPM, is that 400 detonations per cylinder per minute, so 93 revolutions per 7 seconds, and 46 detonations? I think computing the wear from a single (non-premature) firing in a cylinder is going to be a fools game.
Lots of uncited references to the average time spent at a traffic light being 75 seconds, or 20 minutes per day, or 6 months of a lifetime. Let’s just go with 75 seconds. If it takes the car 7 seconds to turn off, then the question is 68 seconds of idle or one start? So what causes more wear, 453 combustion strokes per cylinder or one starting event?
Sure they have. They make sure the additional wear and tear will not cause any failures during the warranty period.
The 7 seconds BS dates from a couple decades ago. IMO utterly irrelevant to a modern car
I could see battery wear being more of a factor in hot climates with auto stop. Heat is tough on batteries to begin with. Perhaps the deeper cycling of the battery from powering all the electrical stuff when the car is stopped puts more stress on the battery.
Used to be that the rule of thumb was that if you knew you were going to idle for more than 60 seconds, turning the car off was the better option, at least as far as gas economy was concerned. This was primarily because carburetors and port fuel injection are less precise than modern direct fuel injection, and starting back up needed more fuel than running for say… 58 seconds. Carbureted engines were especially bad about this- you had to actually crank the car enough to suck enough air and fuel into the cylinders to ignite, which was wasteful.
As I understand it now, direct fuel injection means that when the engine starts back up, there’s virtually no additional gasoline needed to restart, so there’s no fuel economy penalty for stopping and starting immediately like the newer auto-stop systems do, which also means that any time spent idling is wasting gas.
As far as the total cost of ownership goes… from what I understand manufacturers have built beefier starters and certainly batteries (my 2024 has one of those pricey AGM batteries in a much larger size than I’d have imagined) in order to offset the wear and tear of the auto-stop systems.
As far as your MPG vs. CAFE standards goes, I can say that on my truck at least, when I turn auto-stop off, it’s noticeable on the gas economy menu. That idling gasoline does indeed add up.
My personal suspicion is that I’m going to see even more money spent on batteries over the life of the vehicle than otherwise (batteries in DFW are ephemeral things), but that my fuel economy will be better, and the starter won’t be an issue.
When shopping for a new vehicle recently, avoiding this “feature” was my first priority.
I predict it will go away in future automobile models.
mmm
Well, yeah, the whole engine part is deprecated in general-use automobiles. No need when you have on-demand torque from an electric motor with almost no energy usage when not torquing. Engines will be reserved for specialty models.
First point - start used to take a lot of extra fuel to fire - but fuel injection (for the lasr 20+ years) precisely measures the appropriate amount of fuel. Even from cold start when beginning a trip, the starter barely runs 2 seconds and the engine fires immediately in a modern car. (heck, I just tap a button, and the car itself jusdges when to engage and stop the starter) Both cars I’ve had with auto-stop there was a button to disable it. If your car stops and starts two dozen times on a trip, it’s nothing compared to how long engines were cranked old-timey. (Usually, when it restarts on its own, it’s because the air conditioning needs to run the compressor to maintain cabin temp). When you add in my old Toyota hybrid, that’s 3 vehicles I’d had for 10 years, 10 years, and 1 year(so far) and once replaced a battery.
Even back in the 70’s with carburetors and hand-cranking, the logic I heard was a warm start used about 30 secconds of idling fuel, so was a viable strategy for fuel economy, so presumably that 7-second number is not too far off today. The counter-point back then was that starting without fuel injection meant pumping an over-rich mixture into the cylinders, and pushing a lot more incomplete combustion and gas vapour out the tailpipe - much less of an issue today.
I would hazard a guess that restarting the engine within a minute or so of stopping is a lot less stress - the engine is already up to heat and well-oiled enough to minimize wear. That first minute starting with a cold engine and needing to get oil flowing is worse on the car. It would create more wear, particularly parts are not expanded to the size they would be at operating temperatures, and the differential heating stresses the parts.
Whereas my Tesla - the engine stops every time I stop, and zero wear and tear starting again. 
Starting a cold engine is definitely hard on an engine, mainly because gasoline contaminates the oil, and thus compromises its lubrication performance. @Machine_Elf gives an excellent explanation here.
Even with fuel injection this happens when the engine is cold. On cold starts a richer mixture (more gas) is used, because the gas doesn’t completely vaporize. Once the engine is at temperature the extra heat helps the gas completely vaporize, so the engine is run very near the stoichiometric ratio of gas and air.
This is why start/stop systems are disabled until the engine is at full operating temperature.
Not directed at you specifically, but why all of the hate for start/stop systems? Is it purely a belief (possibly true) that it creates extra wear on the engine? Is it the bit of vibration that happens when your foot comes off the brake when the light turns green? Fear that this will be the time it doesn’t start? That it’s different from the way cars worked before?
I’ve only ever had it on rental cars, in which I don’t care about extra wear, and I’ve probably not had an opportunity to figure out how to disable it. I just leave it to do it’s thing, even when it’s silly, such as restarting the engine after a second or two so the AC can run.
Drove one as a rental. It is annoying AF. We have been trained that when you are driving and your car suddenly turns off it is an Oh Shit! moment.
My first encounter with the start-stop feature was some years ago, probably in a rental car. It was not awsome as the experience was somewhat intrusive and felt like it occasionally got in my way, like when navigating a busy parking lot. I definitely came down on the “not a fan” side.
More recently, seems they’ve got the bugs worked out. It’s a total non-factor for me. My wife’s relatively new car is a seamless experience. It doesn’t even occur to me to turn it off.
I’ve only had auto stop in rental and friends’ cars. I’m not used to that momentary hesitation when trying to go. It gives me that “oh shit, something’s wrong” feeling. I’m sure I’d get used to it if it was a car I drove all the time. But all my cars are 10+ years old, so I’m typically in a real-time diagnosing mode when driving and paying close attention to anything unusual.
In our car (2018) the feature works more or less seamlessly. Judging by the noise the engine makes and how fast power is available I’d say the “start“ is such a non-event that the extra wear is negligible. So the “break-even“ would be almost instantly.
I test drove a car with auto stop and discovered that I hate it. It feels like the car stalled, and then I wondered if this is the time it just won’t restart. I asked the guy if there was a way to disable it. He said yes but, every time you turn off your car and come back to it, you have disable it again.
I didn’t know this – ignorance fought! Thank you.
Wow. I am very favorably impressed.
Good point. I think of starting the engine as a somewhat iffy process, a major point in the process at which the car might fail. How far to pull out the choke, and how soon to push it back in, and whether to run with a little choke at first, etc etc. How many times have we heard “It’s flooded!”
The incentives for fuel economy and for reliability may be different, granted. But some brands, the ones I buy, promote reliability. If they don’t publish numbers, Consumer Reports does.
It wouldn’t make sense for the break even time (whatever that is) to be how long it takes for auto stop to kick in. If auto stop is going to kick in, the sooner the better. It’s a problem that the car can’t predict how long you’re going to sit still. The driver has more of a chance at doing this; I know a complete stop at a stop sign without any traffic has 0 seconds as its minimum requirement, and I know busy intersections that might turn red on me as I approach, so I can somehow tell the engine which case to stop for and which case not to. I like the way my Forester does it: pushing the brake further causes the engine to stop immediately, where as barely keeping the brake on never stops it.
Good question. I felt uncomfortable about it at first, because I always fear the moment of starting as a significant risk of car failure. While it’s bad enough if the car won’t start in my driveway, it’s far worse if it won’t start in the middle off a busy intersection. But if they have made the system reliable, this is one of those fears we’re best off learning to forget.
I also don’t see the big deal. We have had at least one car with “auto stop” since 2006 - it was a hybrid, which by definition is an auto stop car. Yes, it took a week or two to get used to the car “stalling” at stops, but that was it.
Now we have one hybrid and one gas-only car with auto-stop. The car with auto-stop has two batteries, one just for the auto stop system. The only time I notice that the engine has stopped is if it’s really hot out and I notice the AC has stopped running (if the temperature inside the car gets too high the engine will restart to engage the AC). I don’t feel anything at all when I hit the gas and the engine starts up again.
I don’t think you can judge auto stop from an occasional rental car. That’s not enough time to get used to the new pattern. It’s like when my dad got his first car with an automatic transmission - it took quite a while before he stopped reaching for the shifter while he was driving.
BTW - from what I’ve read, most people either dislike or are neutral about AS/S. There are very few people who actually like the feature.
Well, I’m one of those who like it, but I have a secret reason: I drive a manual transmission vehicle. With automatics, there is a perceptible lag when the accelerator is pressed, and the engine starts up, which people don’t like. With my manual, the engine starts as soon as I depress the clutch pedal to put it in gear. The engine start-up time is faster than my ability to depress the clutch, shift to 1st, and release the clutch, so there is no time penalty at all. I like that I’m not wasting fuel idling at a light.
The engine in my non-hybrid car starts up as soon as I take my foot off the brake pedal. I have never noticed a lag.