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I have an old car (but with electronic injection) that predates by far start/stop systems which are used nowadays to save fuel (turning off the engine brings savings after 3-5 seconds, see Calculating engine starter’s energy use ).

Does it makes sense to start/stop my car manually when I expect more than 5-10 seconds idling? I noticed that starting the car when warm is almost instantaneous, like 2 seconds.

The starter motor may get additional wear, but after all I rarely hear of failing starter motors... it's a tough component anyway, and there is always enough time between idling to cool down the starter motor.

Edit

For info: the starter motor of my car failed at the 181000 km mark. I still have to check, but very likely due to worn out brushes. This with normal use, no start/stop except sometimes in the last 20k km, so almost nothing. Increasing the start/stop cycles by let's say 5 (meaning 4 start/stops when idling per driving session) would have reduced its life to 30k km, not counting the remaining issues as pointed out in the comments. So, not worth at all.

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I work for a fleet delivery service. Due to safety regulations all vehicles must be shut off at every delivery point. This equals up to 150 stops a day. The starter motors fail with regularity. In most cases 3 times or more a year. Ignition switches about twice a year, and fly wheels every 2 years. While you won't see this type of abuse,stuff will wear out. The vehicles that have the engine off at idle are designed to do this with larger batteries to run accessories while the engine is off. They have larger starters and in some cases the starter is belt drive to eliminate the flywheel. The start feature is computer controlled so the ignition switch isn't involved. You will have to calculate the fuel savings over the parts and repair costs. Due to variations in fuel usage and costs, repair costs I can't tell if you will save enough to offset the cost.

  • How does the start/stop affect the life of the flywheel? – FarO Nov 27 '15 at 18:39
  • @OlafM presumably he is talking about the teeth on the ring gear on the flywheel. – HandyHowie Nov 27 '15 at 19:54
  • I'm somewhat surprised the fleet delivery service doesn't use hybrid electric vehicles. They can stop and start the engine 150 times a day with ease. – juhist Jul 23 '17 at 12:03
  • So you estimate the lifespan of the starter motor in 20,000 cycles, or about 0.1 cents in repair costs if the repair is 200 Euro. Given 0.2 l/h in idling, 1.8 €/l, it's 10 seconds of idling. If the starter motors in S&S engines is sturdier, maybe only 5 seconds. – FarO Oct 18 at 11:51
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Start-stop on ANY car, old or new, is bad for the starter motor as it reduces its useful life.

Newer motors are much more tolerant so the start/stop system does not seriously damage the motor but it surely will affect the longevity of the motor.

To answer the second part of your question start/stopping for every 5 to 10 seconds depends on what engine your car has , if its a diesel engine then doing that procedure is actually less useful since most diesel engines consume extremely less fuel to idle (that is why you see most diesel locomotives are not turned off , they idle for like hours), start/stopping a diesel will consume more fuel that its saving.

On the other hand for a petrol engine, you can perfectly do manual start stop when the engine is warm , not an issue but 10 seconds personally to me feels not worth switching on and off.

  • The usefulness of such procedure with petrol engines is important enough that the start/stop is mandatory or anyway present on most new cars... at least in Europe. Also, I'm not starting or stopping every 5-10 seconds, I'm stopping always when I plan to idle more than that... like in red lights that I know well. – FarO Nov 27 '15 at 16:13
  • The word stress makes me cringe as an engineer; better to say that the useful life of the starter motor is reduced the more you use it – Zaid Nov 27 '15 at 16:36
  • Olafm you are right, petrol cars are much less affected by following this technique so you are good to go – Shobin P Nov 27 '15 at 18:16
  • @Anarach I see your point, 5 seconds is 1.5 ml petrol saved... – FarO Nov 28 '15 at 0:10
  • May I know how you arrived at that number ? – Shobin P Nov 28 '15 at 2:41
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As somebody who drives a hybrid, no, I wouldn't consider 2 seconds instantaneous. My hybrid starts the engine in less than 0.1 seconds. Unfortunately, it feels like one of those DSG dual clutch gearboxes switching when the engine starts at speed, so not completely free of vibrations. But good enough.

Newer hybrid vehicles can start and stop the engine very often due to the fact that fuel is injected and spark is produced only after the engine is at over idling RPM, meaning the oil pump is already feeding the engine with oil pressure before the high loads from combustion start. The motor-generators that start the engine are brushless permanent magnet DC motors and up to the task.

There are non-hybrid start/stop vehicles as well. They have a slightly up-specced starter that still has a limited amount of start/stop cycles. Also, they only stop the engine when stopped, not when driving like hybrids do. So, the amount of start/stop cycles is more limited. The engine wears slightly every time it is started again, but considering the low number of start/stop cycles during the lifetime of such a system, it isn't generally a problem. The batteries are generally up-specced as well, called enhanced cycling mat (ECM). I am somewhat suspicious of the benefit of this limited start/stop system. The fuel efficiency gains are minimal, and the risk of engine, battery and starter motor wearing out is genuine. And the ECM batteries and up-specced starters cost a bit extra.

Some start/stop cars use variable valve timing to reduce the compression (and thus the engine wear) when the engine is stopped and restarted. If your car does not have this feature, the start/stop may cause excessive engine wear if done too often.

If you don't have one of those up-specced start/stop starter motors, I wouldn't stop the engine at stoplights. Your starter motor may not be up to the task to start the engine so often. Similar argument applies to your battery as well.

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