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I was recently in the lucky position to obtain an (almost brand new) Alfa Romeo MiTo, Progression. Like many new cars coming out these days, it has "Start & Stop" technology that turns the engine off when the car is stationary and is put in neutral and the clutch is released. When putting down the clutch again the engine fires back up.

My question then is this:

a) Is start-stop technology bad for my engine in any way?

b) What impact might start-stop have on my battery? I.e. won't it deteriorate battery life with the constant turning on and off? (The radio, fans and lights remain on whilst in "stop"-mode, but not things like the aircon.)

c) Will this technology really benefit me that much with regards to fuel-consumption? I can imagine it will be more economic when stops in heavy traffic become really long or traffic lights are red for long periods, but for the most part when driving the car doesn't turn off for longer than a minute at most before I have to "start" it up again.

As many new cars lately have this technology I imagine that it can't be that bad, but I'm curious as to it's actual real benefits. I can turn this feature off, but I have to do so every time I start my car up for the first time and then I'm stuck with this glaring orange light in my dash, letting me know it's turned off.

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  • You even see this in cars with automatic gearboxes where it's massively annoying since you can't control it with the clutch.
    – XTL
    Commented Mar 20, 2012 at 17:50
  • I would think it would be the most annoying in unpleasant climates since it shuts off your air conditioner...
    – R.. GitHub STOP HELPING ICE
    Commented Apr 26, 2013 at 22:50

6 Answers 6

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I would imagine that this sort of technology would lead to increased wear on your starter motor, as it is being used far more than it would normally be, however I would hope that they would have anticipated this and designed the starter to be more robust than a traditional one.

The battery should be able to cope with it fine all the time it is in good condition. Batteries do, however, deteriorate over time, with a usual life of around 8-10 years at most. I suspect that as your battery starts to deteriorate, it won't be able to cope as well with the increased drain, leading to the car failing to re-start with traditional flat-battery symptoms. How well the electronics cope with this remains to be seen!

As to your third question, I doubt it will help much at all. Getting an engine started needs quite a lot of energy (hence the big chunky battery), and the only way to get that energy is to burn fuel, through your alternator sapping power as it recharges the battery. I don't know the exact figures, but I suspect you'd have to have the engine off for a fair while to save enough fuel to offset the cost of starting it again.

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    thanks for your input, insightful stuff. I'm not so much of a petrol-head (yet) so I'm getting there. What you say makes sense. With regards to the starter motor, however, from what I read and heard on the MiTo, when it auto-stops the car, the pistons are left in firing order so that when it starts up again the starter motor itself is never involved. I'm not exactly sure how this works or is possible, but apparently all that is then needed is a spark from the plugs. Hence, I suppose this then also means not so much fuel is required to start up again. Mostly guessing here, though.
    – DeVil
    Commented May 6, 2011 at 11:06
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    Anyone have any more insights they'd care to share? I've come upon some other info on the web, but none of them really tell me much as to the MiTo per se. Just that Start-stop technology seems to be the way to go in all future cars.
    – DeVil
    Commented May 9, 2011 at 8:45
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    Starter-less engine starting has been around for some time. Take a look at this article: etas.com/data/RealTimes_2006/rt_2006_01_34_en.pdf
    – Steven T. Snyder
    Commented Sep 25, 2012 at 19:40
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    When you stand still for more than 20 seconds, it is benificial to turn off your engine. Leaving it running will consume more than starting it again. With start/stop technology, the car will not auto-stop when for example the car is too cold, battery level is too low. The computer generally has more info than you, and better (car-specific) algorithms. Let it do its job ;)
    – Konerak
    Commented Jan 25, 2013 at 15:05
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    The 20-second rule varies a lot by engine size/type.
    – R.. GitHub STOP HELPING ICE
    Commented Feb 28, 2013 at 1:08
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Potential savings from reduced idling should greatly outweigh any increased wear and tear on starting and charging systems. I answered similar question about idling before (Is idling bad for your engine?). To summarise the negative effects of idling:

  • Fuel combustion is incomplete, which leads to contamination of combustion chamber (glazing), spark plugs (wich reduces their effectiveness), exhaust system (including catalytic converter).
  • Motor does not operate at optimal temperature, which leads to excessive condensation of water vapour in exhaust system, which leads to its corrosion (ergo premature replacement), and increased emissions.

At the same time cost of wear and tear is low (American governmental agencies routinely cite $10 added per year). Roughly, it means if one would expect to replace the starter at 10–12 years normally, now one would do it at 8–10 (I pulled these numbers out of me arse, but they seem reasonable).

To quantify fuel savings we need to consider savings from reduced idling, and savings from avoided performance losses. Research paper from Vanderbilt University (Amanda R. Carrico et al, “Costly myths: An analysis of idling beliefs and behavior in personal motor vehicles.”) based on the survey of 1300 U.S. residents estimates that on average Americans spend about 16 minutes a day idling (4 minutes warming, 4 minutes waiting, 8 minutes in traffic). Possibly, in more compact European or South African municipalities these numbers could be lower.

Let us say we cut American number by about 60% and save around 6 minutes a day. 2.0L 4-cylinder petrol engine burns around 1 litre per hour idling. 6 × 365 / 60 = 36.5 hours/year, or 36.5 litres/year.

Reduced efficiency can cost even more. If a car is driven 1500 km (930 miles) a month or 18000 km (11100 miles) a year, and consumes on average 9L/100 km (2.0L compact), 5% reduction in efficiency leads to 0.05 (18000 / 100 × 9) = 81 litres per year extra.

So average Golf-class 2.0L 4-cylinder compact can consume extra ~120 litres (31 U.S. gallons) every year due to excessive idling. Multiply that by the price of petrol, and see potential savings on the fuel alone.

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    Good answer in that it covers most things in a very thorough manner. However, it completely misses the fact (that on cars not designed for repetitive restarting) that the startup process is one of the harshest things you can do to the engine as it runs with less than the normal amount of lubrication for a few seconds every time.
    – Brian Knoblauch
    Commented Apr 26, 2013 at 12:01
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    @BrianKnoblauch, in that regard I argue that it is the cold start that is most damaging. Once the motor is at proper operating temperature, the oil is at high lubricity and circulated throughout, so the warm start is much easier on the engine. As a circumstantial evidence, many commercial fleets (I worked for national food disributor, seen how they do it) are also more concerned with cutting idling rather than wear and tear. At the same time, reliability still matters, so I suppose they weighed pros and cons.
    – theUg
    Commented Apr 26, 2013 at 16:07
  • 31x4 is 124 year. or $10 approx per month. Not likely to make a differnce to most, especially comparedto other auto related expenses.
    – Andy
    Commented May 4, 2013 at 22:56
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    @Andy, it adds up over the lifetime of the vehicle. Besides, it is only fuel (and would be more significant as fuel prices go up), and only on the small car (Large SUV would see a larger hit. Those people already spend more money per fill up, than I spend whole year on my 250cc moto. No kidding, and that’s my primary transportation). And if you factor in parts and labour for exhaust components replacement (I’ve seen plenty of cars with just over 100 000 miles and rusted out exhaust or broken cat), it gets even higher.
    – theUg
    Commented May 5, 2013 at 8:29
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    @BrianKnoblauch And just what about starting makes it "the harshest things you can do the engine?" Think about what's going on mechanically. The only part about starting and idling that's different is that during starting, there is a load on the flywheel via the starter motor. There is no load on the engine, and all of the same parts are moving in the same way. I agree with the sentiment for a cold start, since there is less lubrication (and even this is much improved with modern synthetic oils), but once the engine has reached operating temperature, starting is not harsh at all.
    – Shamtam
    Commented Jan 10, 2015 at 16:00
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After 3 (three) seconds of idling you'd better off shutting the engine off.

https://physics.stackexchange.com/questions/57794/calculating-engine-starter-s-energy-use

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I don't entirely agree with the accepted answer.

I have read somewhere that the extra energy required to start the engine is about a second or so of the amount of fuel it would consume when continuously running. So, it is definitely clear that the start/stop system saves energy. If starting an engine required a lot of energy, where would the extra energy go, then? It wouldn't make sense knowing the laws of physics. The rotational kinetic energy of the engine is anyway so low that it stops in less than a second if fuel supply is cut. The efficiency of starter motor (and the alternator) might not be 100%, but even a 10% efficiency should mean that starting takes about the same energy than turning the engine for 1 second.

However, does it save enough energy for it to pay back? Probably not. I have 60 000 km on my 2011 Toyota Yaris, and it has a functionality in the car computer for telling how long the engine has been off. If I recall the figure correctly, it has been off for about 13 hours. If the car lifetime is 300 000 km, it will be off for about 65 hours during the lifetime of the car. How much fuel does it save, then? Assuming that 0.7 liters per hour are consumed by an idling engine, it is 45.5 liters of fuel saved. In Finland, this costs a bit more than 60 EUR (in the United States, it would be much, much cheaper due to the lower taxation level).

Now, what does the start/stop system require, then? Firstly, it requires a heavierweight battery. The start/stop system battery in my car is not an AGM battery but it is a flooded battery where the plates are thicker. Probably a bit more expensive than a regular flooded battery. Secondly, it requires a more expensive starter motor that can withstand more start cycles. They at Toyota have indeed taken this into account, and the starter motor has a certain amount of start/stop cycles it can withstand, and it requires replacing if the amount of cycles it can withstand is exceeded (which probably will never happen for most users). Thirdly, it requires the computer program to control the starter motor, but this is merely constant R&D cost without variable per-car cost.

What are the disadvantages, then? I assume that premature battery wear might be a problem. I have noticed on my car that the lights have recently started to momentarily dim when the start/stop system is doing its job and re-starting the engine. But my battery has been in use for 4.5 years, and it might in fact be a good lifetime for a battery.

I have recently started holding down the clutch when on a stoplight, because I don't believe the savings are that great, and because I'm concerned about premature battery failure.

Why do car manufacturers install start/stop technology then if it doesn't pay itself back? I assume the reason is that taxation (annual tax and vehicle purchasing tax) in most countries is heavily based on fuel consumption, and because the fuel consumption driving cycles have an excessive amount of time when the car is stopped. Most drivers never stand at stoplight for as long as in the driving cycles.

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Most modern car manufacturers do proper research, development and testing before they introduce new features in an automobile. Since start and stop technology was not existing some years back, older vehicles will not benefit from this function. Newer cars which already come installed with such features have no problem whatsoever, but it is advisable to shut off this option in extreme bumper to bumper traffic.

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    This doesn't really answer the question.
    – Rory Alsop
    Commented Apr 27, 2013 at 8:14
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Engine has no Oil Pressure when in Stop Mode, Start Cycles will wear out stress Bearings faster from low/no Oil Pressure Cycling with very short time to increase Oil Flow.

Buy a new Battery, then Starter, then Engine !

EPA does it again.

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    While true in general, manufacturers have designed the starter and battery to withstand the worst case stop-and-go traffic. They're also battery level thresholds in case voltage drops too low. It wouldn't be a stretch to assume they've engineered bearing tolerances or even "Accusump" like solution to minimize engine wear.
    – Nick
    Commented Jan 10, 2015 at 15:37
  • @Nick ... I believe Frank is saying to get rid of the car with the start/stop technology, while not really giving a good reason or proof of what he's saying, which you refute in your comment.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 10, 2015 at 20:54

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