Myth-busting: Does stop-start damage your engine?
Plenty of people will tell you what they like and don’t like about stop-start systems. But, does stop-start damage your engine?
PLENTY OF OPINIONATED writers will tell you how stop-start is all about carmakers gaming the system in lab-based fuel economy tests, and to some extent it is, but there’s more to stop-start than that. Sit back and let uncle Isaac learn you…
What’s the history of stop-start?
It was the 1980s, an age of big hair, great movies (Highlander, Ghost Busters, Top Gun, Indiana Jones, Star Wars…) and innovation in cars. Long before some ‘rogue’ Volkswagen engineers decided to game the system in California and cause ‘dieselgate’, some Volkswagen engineers invented stop-start.
Or, at least, it was Volkswagen that first applied the idea to production vehicles. Stop-start was a suite of technologies the brand launched under its Formel E (Formula E) brand. Think of it as BlueMotion before BlueMotion. Under Formel E, the relevant Passat, Polo and Golf (be it petrol or diesel) would be fitted with aerodynamic bits and bobs, tweaked transmissions which featured a tall top gear, (called an e gear) for fuel saving while running at a constant speed on the highway. The Formel E kit also included a gear shift indicator which via a yellow light on the instrument panel would advise when to shift up a gear for maximum efficiency.
But the main piece of kit was stop-start which you would activate by pressing a button on the dash and then pressing it again to turn the engine back on, or when you slotted first gear in a manual car.
Unfortunately, stop-start didn’t catch on. Not in the 1980s, anyway. It reappeared in the 1990s in hybrid cars and wasn’t until 2013 that it really became a thing in cars. Yes, really.
So, what is stop-start?
Once the vehicle is stationary the engine is killed until the driver either dips the clutch and slots a gear (on a manual vehicle; to activate it the driver needs to put the transmission into neutral) or you come off the accelerator pedal and onto the brake and stop the car (on a vehicle with an automatic transmission). In most applications, the stop-start defaults to on but it can usually be deactivated via a button on the dashboard; although it will switch back on every time the car is turned off and on again with the key. The thinking behind it is that it saves fuel and emissions that might otherwise be generated while the vehicle is idling away at a set of traffic lights.
It’s worth remembering here that stop-start will only work when conditions are ‘just right’, meaning, if it’s too cold or too hot and the HVAC is working overtime to keep your warm or cool then the stop-start will switch off the engine but then a split-second later turn it back on again to prevent the battery from being overloaded. And it’s rare, even when conditions are right, that a stop-start system will keep your vehicle’s engine switched off for more than 90 seconds.
Does stop-start cause premature wear and tear?
The widespread application of stop-start has only been possible because of improvements in things like battery technology, bearings, oils and control systems in vehicles. See, asking an engine to stop and then start again places strains on components. Indeed, if you took a starter motor from the 1990s and looked at one from today, the modern starter would be much stronger capable of handling up to 500,000 cycles in its ‘lifetime’ – the older starter would have only been designed to handle around 50,000 start cycles. All sorts of things are different, from the type of bearings used, to the long-life brushes, the way the solenoid works, the wiring (beefed up). The aim is to make it easier for the starter motor to do its job.
The same with the battery which is now a much stronger thing than it was in the 1990s, and that’s because when the engine’s stopped, but we still want to keep our lights on and listen to music and run the heating or cooling, and then start the engine when the lights turn green. Beyond a beefed-up battery and wiring harness, some system utilise a separate battery for restarting the engine while the main battery worries about everything else, and some use a capacitor that stores a charge to jolt the starter motor. And then there’s slicker, stickier engine oil that will stay on the moving parts when the engine is stopped for longer, and bearings which are now slipperier via lubrication but also in construction.
Practical Motoring spoke with the technical boss at a leading car maker who said that stop-start doesn’t cause additional wear and tear on an engine but that the owner must adhere to the recommended service schedule and use the manufacturer’s recommended oil. “Using cheaper oils can cause more damage to your car’s engine than anything else,” he told Practical Motoring. “Operational stop-start causes no wear and tear at all; wear and tear at cold start-up is a thing, though,” he said.
Does stop-start save you money or fuel?
Well, this is the question that generally send the internet into meltdown. It’s a personal thing, I think. For me, stop-start saves me maybe a couple of cents worth of fuel a week, but that’s simply because of the driving I do. Long stints between stops. But, if you’re in stop-start traffic then it’ll be more active and save you a little more than it does me.
It does mean there are less tailpipe emissions, but when you consider the vehicle will only stop itself for a maximum of up to 90 seconds in best-case scenarios then the overall saving can be measured in cents and a fistful of dollars only over time, rather than hundreds and thousands of dollars.
In terms of fuel, the savings will be about the same… it’s a tiny bit here and a tiny bit there. And while some will suggest that’s a good enough reason to switch off stop-start, I’d argue that the ability to save every bit of dead dinosaur essence you can is worth it.
Is the point of stop-start to save money and fuel or allow car makers to make a better fuel economy claim?
Well, this depends on who you listen to. Yes, the idea behind it is to save money and fuel, but some argue it’s so that car makers can game the system; meaning, when it comes to the lab based fuel consumption test. You can read more about how that works HERE, but in a nutshell a car is plonked onto a rolling road and run for around 20 minutes in two blocks of 10 minutes. A large chunk of that simulation is intended to recreate stop-start running and so some argue that those with a stop-start system gives an advantage to those that don’t. But that’s only sort of correct. See, most, if not all new cars now come with stop-start as standard, especially in the most competitive segments, and because stop-start will only idle-stop the car for a maximum of around 90 seconds the advantage would be minimal.
The usability of stop-start…
It used to be that these systems were very rough. Indeed, they were so rough that in the US, people complained about the BMW 3 Series when stop-start was first introduced on it that it was recalled and the system redesigned. And I’ve driven vehicles where you can take your foot off the brake and count to three before the thing fires back into life.
Stop-start systems, be they on a petrol or diesel vehicle, are, generally speaking, so smooth you’ll barely notice when the thing’s shutdown and, by the time your foot has come off the brake pedal the car has started again and you’re off and running. Some systems even respond to a jink of the steering wheel. Or there are those that are clever enough to determine when you’ve slowed down almost to a complete stop but have changed your mind and jumped back onto the throttle again… even though the system has started its stop cycle, it’s able to cancel that in a split second based on your throttle application and keep you moving; Subaru’s stop-start system does this very well, for example.
In the end
Stop-start is a clever system which while it won’t save you huge amounts of fuel or money isn’t necessarily a bad thing, because every little bit helps, right. But, if you’re one of these people that absolutely abhors stop-start then you can, in most cases, just turn it off – Just remember you’ll have to do this every time you get in your car because the default is for it to be active.
Question: Does your car have stop-start? What do you think, and do you use it?
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44 Comments
So what your saying is, the system won’t save you money or fuel? The system only works in ideal conditions (like when is it ever hot in Australia)? It will only stop for 90 seconds at a time, so what happens in very heavy traffic jams, does it start/stop several times if you are stationary for 5 minutes? and no matter how you phrase it, there is always a delay for the restart and even on most current models the refinement of the restart is terrible.
So wheres the benefit here?
My 2019 Subaru Forester has auto stop/start, and the jolting restart is extremely annoying. It’s also dangerous to be paused if there is a need to move away from the stop quickly to avoid collision or other danger. My other car is a hybrid and does not have these issues because the motor initially moves the vehicle while starting the gas engine. I decided to test the fuel consumption on my Subaru for 30 days with and 30 days without Auto Stop/Start. I drove about 1,000 miles each month. My Southern California commute includes both cross town traffic with many stoplights and congested stop-and-go freeways, which should make the most of Auto Start/Stop. I got slightly better fuel economy with the Auto Stop/Start disabled. 21 MPG with the feature On and 22 with the feature off. Without a fully controlled test, it’s not realistic to claim that Auto Stop/Start causes more fuel consumption, but it is safe to say that AUTO START/STOP ABSOLUTELY DOES NOT IMPROVE MPG ENOUGH TO BE A BENEFIT TO YOU. After my test, I did some research because I wanted to understand why a car manufacturer would force such an annoyance on people without providing a benefit. I found that the feature improves emission ratings which equate to more money for the car company from government programs, and thus more profit. I bought an “Autostop Eliminator” module, and highly recommend that anyone else annoyed by this disservice to consumers do the same.
I just purchased a 2020 Forester, the window sticker read 26 city, 33 highway. How can they blatantly lie like this. I’m getting 18.6 combined. And hate the stop/start function. Where do I buy the module to cancel this function and does it impact the warranty?
I’m looking at the 2020 or 2021 Forester now and the start/stop is a big draw back for me. On the 2021 you can shut it off I believe. Any other insight on this vehicle you can offer?
I just bought a 2020 Forester two days ago…..take yours back to the dealer NOW. I live in the deep mountains and get 25.1 average after a couple hundred miles of driving. There is something wrong with your ride. This is the Touring edition, if that helps.
Push the Acircle button until it is yellow to disable but you will have to hit it every time you get in.
Buying a Subaru was your first problem.
I wanted to get a Subaru Outback, but then I found out how stubborn they are about having the engine stop/start, and the CVT transmission. They probably have Cylinder Deactivation, also. Not too long ago, the Subarus were having majore problems with their head gaskets. I wonder if the Engine Stop/Start contributed to that problem? I got over the Subaru and bought a 2021 Mazda CX-5 w/turbo and AWD. It doesn’t have iStop (the engine stop/stop), or Cylinder Deactivation, and it comes with a 6-speed automatic instead of a CVT transmission.
We recently bought a Mazda 3, and if the car was mine, instead of my wife’s, I would turn the stop/start off as I think it is a waste of time for cars in Cairns, because of the lower traffic levels and the hot weather.
What really annoys and disappoints me is the Mazda 3 startup procedure. On starting the car the engine revs to 1500 rpm for about 20 seconds, then slowly drops back to an idle speed of 800 rpm. The Mazda people told me that this is to warm the car up quicker, but as your story above notes, most engine wear occurs at cold startup, and no-one in the world could convince me that revving the engine to 1500 rpm from cold doesn’t contribute to increased engine wear.
Of course the numerous times that we test drove the cars this didn’t happen, as the cars were already warmed up from being driven that day. I honestly would not have bought a Mazda 3 if I was aware of this, and I really feel like I have been conned. Not happy Mazda.
I bought a new 2021 Mazda CX-5 w/ turbo and AWD, and it doesn’t have the iStop. Some mechanic at the Mazda dealer said, the new Mazdas CX-5s in the U.S. didn’t have the iStop this year.
As for older Mazdas that have iStop, you can easily disconnect the iStop under the hood by the latch. A plastic plate comes off, and then you use an “L” shaped phillips to take off one screw, and then move the sensor aside. There is a YouTube video that shows you how easy it is to disconnect.
Peugeot have dropped it on Australian spec cars even after beefing up the starter system. The cars I driven, including the Subaru Forester & Nissan Note manual (Europe) were OK. Some are still slow to get away. I can see the advantage in long traffic jams in clean air and reduced fuel consumption, but what about air-conditioning in Australia’s warmer/hotter conditions, it runs all the time?
yes, my car has stop-start. (new Golf Alltrack)
No, I don’t use it. I turn it off. I forgot a couple of times, and it wasn’t a problem, it was unobtrusive.
But you won’t convince me that it doesn’t prematurely wear out starting components. For little gain.
Front and Rear Cross Traffic Alert would have been a lot more useful, and a power tailgate.
Both of which are inexcusably left off the Alltrack.
As is fresh air ventilation without the climate control switched on.
But I suppose i shouldn’t complain too much. I bought the car. And the windows do open.
Yes and yes. It works fine. Any delay is microscopic and is only a concern if I am the first car at the lights.
48v mild hybrid will solve much of the drawbacks of stop start and improve fuel economy by ~10%
Hard to argue an overall saving when the extra cost of a new battery suitable for stop-start equipped cars may wipe out any savings stop-start may have made.
I just don’t like stop-start overall. My Mazda has it, so far I’ve “saved” enough fuel to run 20 kilometres, and it took me 11,000 km to do that. Let’s be generous and say that’s 2 litres of petrol saved, $3 or so. But my car’s a manual, and stop-start kicks in less frequently than in an auto (and yes, despite not really liking stop-start I usually leave it switched on).
Having said that, I do like some aspects of stop-start. When stopped at lights that I know are going to be red for a while it’s nice to have the engine switch itself off, you get a bit of peace and quiet.
Take a nap when you get home.
Yet another reason I opted for the I30 SR!
I get it,but what about safety.Engine off,gear in park,look in the mirror…this guy will never stop in time,i am about to be rear ended.In other words i have no control.If the engine is running and the gearbox is in gear..,split seconds count here,i can try to get out of the way,or at least try to do something.I am in control.
Exactly, Fred. I bet this situation wasn’t thought of.
In my 2020 Ford Ranger the engine starts back up as soon as any pressure is released from the pedal and the start is instant. For me, I can’t imagine that being a problem at all. Can’t say the same for other vehicles.
Own a NXLexus, hate the stop start system, first thing I do after start is to turn it off, for the thimble of fuel saving, the vehicle tells me how much fuel it’s saved me, it’s not worth the trouble.
Not so good in traffic when you have to wait for a restart to leave the traffic lights, wish I could permanently turn it off.
It might not save you much money on fuel but it’s much more pleasant for pedestrians walking alongside a traffic queue if the vehicles have stop-start enabled.
It isn’t just hard on the starting parts, you are taking off from a dead stop right after the engine is started. That’s demanding a lot of power from the engine who’s oil isn’t circulating yet. Over and over. Typically I let a engine warm up a bit at idol before demanding a bunch of power from it. I think much of the push behind this system is to require auto makers to buy deep-cycle batteries, Johnson Controls batteries in particular, who claim the AC still runs with the engine off in their promo video. Not possible, the AC is belt driven by the engine. I’m starting to think a second reason behind this is a move to disposable cars because the piston rings are going to be shot in I’d guess 3 – 5 years, then the cars will be smoking so much they won’t pass emissions testing.
Its not about the battery, who cares for battery. Its not about starter, who cares about a starter, its not a big deal if it goes prematurely. They last 20 30 year anyway. The wires does not need to be beefed up and they are not compared to cars without start stop. Its about turn off hot engine, stoping circulating oil and water, its about hot spots here and there. Inside the engine head, engine block and its about turbocharger. You just dont want to engine to stop sudenly when is very hot in summer in the city or after spirited driving. That s not good for any engine – period. If the engine have better crucial parts (but they don t) that does not change the fact that without using start stop, theese parts will last longer. How long, it depends on many factors. When you turn off hot engine the temperature inside engine will rise. That s pure physic. And then there is a turbocharger. Stoping engine suddenly when turbo is at its peak temperature is not smart move to do.
Start stop monitors engine and turbo temperatures. It will not engage if too hot. At least my 2021 KIA does.
We only do short runs in our Mazda3, and I-Stop only activates two or three times during the average journey. Annoyingly, it cuts the engine when stopping briefly in the driveway to unload passengers or shopping items.
I’ve simply disabled the system by adjusting the “service” switch in the engine compartment.
There’s a scam operating concerning the battery requirement for i-Stop; Mazda will tell you that you need a special battery, and wants to sell you a very expensive replacement. When I need a replacement, I’m just going to get a good quality standard battery.
According to ASME, 85% of engine wear occurs during starts as the oil film on rotating and rubbing surfaces doesn’t exist. Start stop has to cause extra wear because the oil film takes time to form after the oil pump starts. An auto manufacturer doesn’t care because it will be out of warranty when the engine fails, but it will fail earlier than an engine without start stop. Also, having a $50k plus vehicle using start stop to save a few dollars a year in fuel costs is pennywise pound foolish. It is a dumb illogical unscientific feel good climate change response.
On my Ford Fusion the Start/Stop will not engage unless the engine is warmed up. Also, it does’t operate if the A/C is on or the cabin has not warmed up to desired temp. So all the concern about starting and stopping a cold engine does not apply to my vehicle. Plus, whose car goes into Park when the Start/Stop is on? That’s foolish. Mine starts almost immediately…in fact, I don’t know how it does as it doesn’t seem to be the same way that the engine starts from a normal off condition when I get into it….there is no typical “cranking” sound. Lastly, I have a very accessible on/off switch on the console so if I don’t want it, a simple finger press turns it off.
Every time the engine starts it turns the crank without oil for the 1st few revs until the pump gets oil through the ports to the bearings. The more times the engine starts the more wear occurs
I own a 2013 BMW X1, and I’m having an issue reading start stop future. The car stops at the traffic light, but it doesn’t start how it suppose to do. I need to shift to the park position, then press the button, and restart the car in the middle of the intersection. Does anyone has the same problem?
I don’t like the fact that the steering wheel, is without power assist
I have the 2020 Ford Edge with Auto stop start. Only time it really bothers me is when I park. As soon as I come to a stop the engine stops, then immediately restarts when moved into Park, just to be turned off again.
just bought a RAv 4 2021, must admit the start stop feature is annoying, and i can’t really see the savings with my driving. The good thing is the systems seems to recognise when its safe, for example , the engine will not turn off when the heat or AC is running or if the engine is not warm . Not a fan but I can turn the system off with a button on the dash.
Of course the Engine Stop/Start technology (or iStop, ESS, etc.) wears down most of everything that’s associated with the engine. It’s a very reasonable assumption. The starter, the battery, the flywheel, the cylinders and piston rings, the bearings, alternator, water pump, etc.. Every time the engine shuts off, the oil flows back down into the oil pan, and every time the car starts, there is much more friction on the cylinders and bearings than if it just kept running. Every time the starter engages the flywheel, there is more wear and tear on the teeth
I’m very happy with the 2021 Mazda CX-5 turbo/AWD that I bought a couple of months ago because it doesn’t have iStop, Cylinder Deactivation, or a CVT transmission. I wanted to buy an American-made car, but they didn’t want to listen to the customer.
Nice article and thank you for this valuable information
I have it in a 2021 Honda Passport and mentioned to the dealer that I hated that feature when I test drove the car. He said I could turn it off, but did NOT clarify that I had to turn it off EVERY TIME I start the car. That would have been a deal breaker for me. I CANNOT stand the feature and wish I could turn it off permanently.
Used to be engineers said that much of the wear on a engine happens on startups when oil is all in the bottom of the pan and is not circulating throughout the engine. Now we add in a start stop technology that on a hot car would cause heat soak to set in because a engine simply stops circulating oil and coolant. How exactly is that good for a combustion engine?? Especially today when engines run hotter, put out more horsepower per liter and in general produce more heat? Add in a turbo charger which will also loose that oil pressure on a start/stop vehicle and you have a recipe for a engine that will have problems down the road. All in the name of saving gasoline which if any savings does occur you will more then make up on more repairs. It’s one of those decisions car makers made just to meet a EPA goal that means nothing to a owner. It’s troubling that the trade offs are simply not worth it for a owner. Car makers did no favors to the future owners of these vehicles down the road.
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What i read is that a new vehicle is bigger, heavier, and more expensive to purchase and maintain to include a feature with dubious benefits. Did i misunderstand?
There are companies now making plug in devices that go inline with your cars wiring to turn off the auto engine off feature permanently so you don’t have to push that button every time you start the car. Just google it.
So larger wiring, starter, thicker bearings, larger battery weight how much? Isn’t the small amount of fuel saving defeated by the extra weight of the vehicle’s beefed up parts?
The only time I dislike the auto stop start is when I’m got to or coming back from Florida to Michigan. In heavy traffic or more precisely a traffic backup where you move 2 feet stop and engine stops a few seconds later you move another 2 feet and so on. Sometimes my engine sputters when it comes back on and it can’t be good on the starter being in at least 1/2 hour backup.
I have it, I don, t use it, I’m fine as normal driving as I get good mpg already, and what you failed to mention to readers, is that all cars use more fuel when you switch the engine back on, so know the fuel savings are a joke. Its just a selling gimmick, like oh I have these silly led headlights, but oh hey they actually are far too bright and blind people in front of me, and oncoming car drivers, yes I hate led headlights, they suck.
I have a Merecdes 180D, the stop start us hardly noticeable, however, it has stalled a couple of times at traffic lights, when I think I’ve jumped the gun a bit. I think the idea that it saves money,in the long term, is contentious For one thing, you can’t fit a normal battery, to a stop start car and a replacement is considerably more expensive. I do tend to turn the thing off most of the time, when I remember, but the car is usually used for short journeys, so I don’t really see any benefit, for myself or the environment.
Certified master tech here for honda.
The auto stop start feature isn’t worth it it does wear out you starter and battery faster.