Hypermiling. Save gas or money?
 

Hypermiling seems like a good idea at first glance.
I'm sure it saves gas but what about the wear and tear on battery, starter and other mechanical devices used when having to restart so much more frequently? Over the life of a car if hypermiling means you had to replace 1 more starter or an additional battery would you save money?
For example - You stop at a red light that you know is a longish one so you turn the car off. Well if you commute in the city/suburbs that might apply 3 to 4 times a day. That's a lot of cranking on that starter, key and battery and it has to wear them out quicker. What do you think?

I haven't seen hyper mileing associated with the auto start stop function which is what you appear to be talking about here. The short answer from a mechnical standpoint is that it would not be recommended as a matter of course for things like the red light in your example for a car that isn't equipped with an auto start stop function like that in say a hybrid like the Toyota Prius. Cars that are designed for auto start and stop have heavier duty starters and larger battery cranking capacity batteries.

In a nutshell, yes if you regularly start and stop your engine at red lights you'll be buying more starters, it really shouldn't hurt a normal battery as long as you're not doing it at every light but a few times a day over the course of several miles. Starters are expensive and labor costs if you're paying a mechanic to install it can be high, especially on modern transverse engines installed on front wheel drive vehicles. I would suggest doing this only in situations like a rail road crossing where you can see a large freight train that is slow moving and you're sure that you'll be stopped for several minutes, for 20-30 seconds at a red light you're just increasing your vehicle's lifetime service and repair costs IMHO.

VW themselves suggest that you turn off your engine if you know you will be stationary for at least 15-30 seconds. Once the engine is hot, it starts pretty much instantly without much cranking, so I don't think a hot-start causes much wear.

'Hypermiling' potentially covers many different things. Many are things that good drivers should be doing anyway (maintain lots of space in front so you can anticipate traffic, don't do jackrabbit driving between red lights, etc), some are potentially risky or unwise which are advised against (drafting for example).

Killing and restarting the gas or diesel engine frequently with only short 'off' times doesn't seem like a good idea for more reasons than just the electric starter and solenoid - - I would definitely research this with a real mechanic, not just public opinion. Assuming a engine driven cooling fan and/or coolant circulating pump, during the 'off' you are going to be un-naturally cycling the temperature. I also would question it's benefit on diesel systems with DPF and urea injection. Another consideration: not sure how happy the high pressure fuel systems (gas and diesel) will like being cycled. It has to add wear on the starter sprocket, engaging mechanism and flywheel - whether or not they are HD.

More good would come out of better driving habits - like MMUK (above) mentions: lots of space (so you are not decel/accel), jackrabbit driving, watching/anticipating traffic speed many vehicles ahead.

I often stop the engine on my motorcycle when I'm approaching a red light or I'm before an apt downhill leg and I had no problem with the starter during the last 80k km / 50k miles. What I had problem with is the drop-out bearing of the clutch, much P&G could definitely hurt it. But I don't regret, without a control group I can't guarantee it would have lasted much longer under more normal circumstances - I don't see many bikes over 100000km around.

The 'new' clutch plates have already outlived the old ones I used when I still did engine brake instead of coasting, and my front brake pads are over 32000km (20k mi) now, rather long life compared to 'normal' riders' ones. Rear ones were replaced at 108000km...

Lower average speed and less braking saves tires too, while P&G wears the rear somewhat more. This is how I ended up wearing 3 rear Heidenau K73s for a front one.

I would only add that your engine is only consuming just a tiny fraction of the fuel that it burns as you drive. Even with the air conditioner on, the injectors are only delivering just enough fuel to overcome the internal engine drag and oil pump drag alternator drag and compressor drag, water pump, etc. May be less than you think.

https://www.gassavers.org/f9/the-reas...lved-3423.html

https://www.consumerenergycenter.org/myths/idling.html

Good links.

Thanks MMUK