Idle start-stop feature necessary? Discussing its pros & cons

Idling auto-start / stop helps many manufacturers meet fuel efficiency & emission norms in several countries.

BHPian PrideRed recently shared this with other enthusiasts.

A lot of manufacturers these days are offering Auto start/stop functionality in cars. The functionality is available from budget cars to premium cars. While the intention and functionality look the same from an end-user perspective, I believe the implementation is different. There is some sort of logic that goes into each car and when you drive for some time, you start noticing differences. That said none of the manufacturers has been able to get this right. What is annoying though is other than switching off the functionality there is no additional configuration available for the user. Almost all the manufacturers keep this feature on by default and one must power it off every time after starting the car.

Positives

• When things work, it's convenient. Release the brake pedal and you are ready to roll.
• Saves some fuel, though I believe it’s a small percentage.

Negatives

• Most implementation is absurd. For example, In Suzuki, the engine shuts off when I try to slot from R to D.
• Frequent start/stop will affect components like turbo, battery, starter motor etc.
• Frequent start /stop might negate the benefit of fuel savings?

I don’t see many good bits and the negatives outweigh the positives. So why are manufacturers pushing this? Just a trend? I am sure there is some cost involved to implement, maybe a bigger battery, some coding, a button etc. I read many reviews/ownership posts and this functionality is not highlighted much nor is a deal-breaker for any. At the end of the day one can switch it off by the press of a button, but feel this feature is there just for the sake of it. What are your thoughts?

Here's what GTO had to say on the matter:

Idling auto-start / stop helps many manufacturers meet FE & emission norms in several countries. Also the reason many ATs have ridiculously tall 7th, 8th & 9th gears.

I hate the feature. Have disabled it on my 530d (used to activate by default every time I start my car), and it's the first "off" button I press in any new car I test-drive. Got to admit, a few manufacturers have learnt how to make the engine off & restart action relatively smooth, although, in a majority (especially big diesel), the experience is terribly annoying with cabin shake etc.

Here's what BHPian sreejithkk had to say on the matter:

My 2019 Ertiga ZXi+ has this feature and I like this feature. It is seamless, and except for the driver, none of the passengers notice that the engine was shut down and restarted due to the lack of any vibration on restart of the engine. Maybe it is because Integrated Starter Generator is used to restart the engine. Also when the cabin temperature increases, it restarts the engine automatically so that Air Conditioner can cool the cabin. My belief is that, since it uses ISG for restarting the engine after auto stop, it will not affect the longevity of the starter motor. And it definitely helps fuel efficiency. So I am in for this feature if the implementation is similar to or better than the one in my Ertiga.

Here's what BHPian Shreyans_Jain had to say on the matter:

Nay.

Useless and inconvenient ‘feature’. AC switches off as soon as the engine cuts, and the continuous start-stop puts an extra and avoidable load on the battery.

Here's what BHPian Kottayamkaran had to say on the matter:

My parent's 2021 MY Ciaz Alpha AT has this start-stop system as part of the smart hybrid system. I find it really annoying and useless. Maruti's smart hybrid is just a gimmick and not useful at all. On a recent trip to Kodaikanal, I forgot to switch it off and while climbing the ghat the car turned off when we encountered a traffic block. The brake pedal became hard (not sure if due to the start-stop system) and the vehicle started moving backwards. Luckily there was no vehicle just behind us, else would have resulted in a mild accident.

Here's what BHPian Axe77 had to say on the matter:

I HATE it! Voted Nay.

In my BMW 3 GT, the default setting was it would be ON and you'd have to press a button to switch it off. I changed the system with the help of a friendly neighbourhood coder and flipped the default around to OFF. Never used it since.

In many metro cities like ours, it really does not make sense to me at least and my intuitive sense is it's unlikely to be beneficial to the car either in our extreme bumper-to-bumper conditions.

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