There was an article on hypermiling in the Washington Post on Sunday. One of the points made there was to turn off your car’s engine when stopped at a long light.
Now, I gather a slight bit of extra gas is required to restart the car, so if you’ve just turned it off for a second or two before restarting, you’ll wind up expending more fuel.
Any ideas on what the payoff period is for such a maneuver? There are certainly plenty of lights around here (DC metro area) where one’s redlight wait is likely to be a minute or more, but what if you only reasonably expect to have a 10-second wait?
You start the car using the battery. Car batteries generally are not designed to have to start the car every 5 min, if you keep it up it is likely you will run out of battery juice at some point.
Cold starting a car is very hard on the engine, mainly because the moving parts in the engine are moving before the oil has had a chance to fully lubricate everything. Now you are not talking about cold starting a car but starting it every once in a while, which will make it somewhat less harmful, as a still war engine will still be somewhat lubricated, but it’s still not something I would want to do.
You can see that on a car like a Prius, it is fairly simple to implement ways to avoid these issues, but not on a regular car.
We have discussed this before, and IMHO the payback period is about 45-60 seconds or so. This assumes that you are driving a modern fuel injected vehicle, the engine is warmed up, and the car is in a good state of tune.
I would note that if you shut off the car at every stop light you will probably wind up with a partially depleted battery, as the engine will not run long enough to rechage it before you shut it off again. This is not a good thing. Also the AC stops when you turn off the key.
Count all the traffic light stops you make during a typical week. Multiply by some number, say 60 seconds, to find out how much you have to idle doing nothing. Use that amount of time to reduce your overall weekly driving. You will achieve a similar amount of gas savings without the wear and tear on your battery and ignition system. Bet still, strive to reduce your overall driving for even greater savings.
While the Post article may have good intentions, it appears the writer did not do some basic commonsense research. The writer probably isn’t a Doper nor has ever heard of the SDMB.
The latest BMW’s turn off the engine at lights or other stops in traffic.
I recall them doing this some years ago. Whether they have done this in the interim period I couldn’t say but I am sure my daughters and my son in law’s BMW 525’s don’t have this option.
It would be interesting to see if there is any discernible improvement in economy using this system.
I’m almost certain they don’t. You must be thinking of their “regenerative braking” system, by which the alternator is only powered during braking. This is done to improve acceleration and horsepower, although it may also have some minor benefit for fuel economy.
One thing to keep in mind is that this technique requires using the starter more, perhaps a lot more for some driving/stoplight patterns. While money can be saved from using less fuel, at least some it will eventually be spent replacing the starter sooner than would have been needed otherwise.
I used to do this at a particularly long light when I lived in California. One thing not yet mentioned is that the cranking time for an engine that’s only been off a minute or two is very short, much less than starting cold. I barely had to turn the key, presumably because the engine is hot and still well lubricated.
A number of cars have this feature built in; it’s called ‘idle-stop’. I think at the very least they have to beef up the battery and starter motor. I got a lift to Toronto once in a Honda Insight that did this; its ‘starter motor’ also provided power assist during acceleration as a ‘mild’ hybrid.
Yup - I recall a Volkswagen back in the 1980s that did this. Shifting to neutral caused the engine to stop (once it had warmed up). It would restart when you moved the gear lever back into 1st.
It didn’t seem to catch on, though, so I had assumed the idea was, um, a non-starter.
I can only ever imagine this idea working on hybrids or manuals. We’re in the USA; hybrids are still a tiny segment of every vehicle on the road, and for that matter, so are manuals.
In my big, fast V8 automatic, I’d be upset at the hesitation it takes when I step on the gas pedal. I supposed in a manual, at least I’d have control. Throw it in neutral, it stops. Put it in gear, it starts. Leave it in gear when stopped with my foot on the clutch, and the engine stays running. Actually, I like that idea very, very much.
I wish it weren’t so hard to get a full-sized car (a real, EPA full-sized car, not “rental company” full-sized) with a manual transmission in the USA. I really loved the giant Opel I drove a few months back.
It’s possible to do this without the starter and car companies have experimented with it. Not sure how reliable it would be. It requires a direct injected motor and a fully indexed crank. The computer injects fuel in the cylinder on the power stroke and then ignites it in sequence.
There a lot of companies coming out with start/stop engines (Citroen, BMW, Chrysler etc…) and they probably all use high efficiency starters.
Alice Gordenker, in the Japan Times: “[It is not true that] repeatedly restarting your car is hard on the starter…”
Easy to say, but I seriously doubt she has any evidence to support this contention. While I wouldn’t choose the term “hard” on the starter, it’s simply not possible to use a starter, say, 16 times during a round-trip commute instead of 2 times and not cause more wear on it. Not that it’s necessarily 8 times more wear, but it’s more wear.
Well, I know little about cars, but BMW have had Donald Sutherland touting their wares on TV for a couple of weeks now, passionately thanking stop signs for letting Beemer drivers save a little money on petrol.