Fifth Gear experiment: Do Stop/Start Engines Make A Difference?
 

https://www.youtube.com/watch?v=-BYkKa1Jo3U

Test car was a Renault Megane with 1 liter of diesel driving the same route.

Results:

Start/stop disabled covered 12.8 miles and resulted in 58 MPG UK

Start/stop enabled covered 14.2 miles and resulted in 67 MPG UK.

Wish my car came with that. I only turn off the engine if my car is warmed up and I'm at a really long signal light (3 min or so?), waiting in line, or waiting at a railroad crossing.

I saw this video a while ago. That's the same engine as my Renault, and the same S/S system which is very good, I use it all the time. It's surprising how well it works, even in mid summer with the AC on full blast. It's not as good as that on my Honda though, which switches off the engine at around 20 Mph if you dip the clutch, and also allows you to exit the car to take pictures or open gates etc, where as the Renault assumes you are leaving so switches off the cars ignition etc.

Big difference in not having it though, they beef up the starter motors to compensate for the extra work load apparently.

I think most cars advertise between 3 and 10 % savings on gas in stop and go traffic. Half owners who have it same to hate it as most cars are set up as it is the default and it has to be turned off every start. Takes a while to get used to but works well on my car. One trouble is in the summer with A/C running the car may start and stop a few times at long lights. Over all a great function.

They also beef up the battery as well and in Mercedes they have a separate battery for electronics and ABS brakes.

LOL, I remember once doing a "Chinese Fire Drill" in an Audi with Stop/Start. The key stayed in the center console the whole time, but I was dismayed when I got in the driver's seat, and it would not shift out of Park, and the light had turned green! Had to push Start again to get going.

GM's system also has a second, deep discharge battery in the trunk.

Every system has it's quirks, I prefer the simple systems myself as in the Honda, it's instant, and as I said, you can get out and spend a few minutes out the car, get back in, put the car in gear and it fires up again.

I think VW started using stop/start as early as 1978, but perhaps there are earlier examples?

I have an Audi Q5 3.0 TDI with the function, and I typically leave it off. I'm not convinced that the small amount of fuel savings will offset the additional wear due to the frequent engine starts and stops. I'm still receptive to incoming info about this, though.

From memory, Volvo did some testing, after beefing up the starter, and they did 175,000 starts before they detected any wear on the starter motor. As I mentioned, these systems have been used for almost 40 years by VW/Audi, I'm sure they've learnt along the way ;)

The motor oil isn't going to drain off of all the surfaces in the short amount of time of an off period with these systems. Normal start up engine happens because there has been hours for the oil to drain into the oil pan. Then new engines use low friction technologies for improving efficiency that also help reduce that start up wear.

The real concern is with the battery. A car company might skimp on upgrading it, which doesn't hurt on the tests, but will result in short battery life for the customer.

A factiod on the starter, Wayne Gerdes is ahypermiler promoter, and makes regular use of the advanced techniques. The standard starter on his Accord needed to be replaced after three years of regular forced auto stops, but the average fuel economy of the car rivaled that of hybrids and diesels.