Shutting engine off at traffic lights with an automatic transmission
 

My apologies if this is in another thread, but I couldn't find a cut-and-dry answer after searching for a while... With an automatic transmission, is it beneficial to your FE to shut the car off at a red light and then restart it when the light turns green? I understand that there will be greatly increased starter wear, but remanufactured replacement starters only cost $110 for my car, so if the savings in gas over that time would be more than $110 (about 44 gallons of gas as of today's prices of ~$2.50/gal), then it would be worth it.

And if it is worth it, what is the correct procedure for doing this with an automatic? I heard you have to shift into neutral, stop, turn the car off, turn it back on, then shift to drive and wait for the transmission to re-engage before letting off the brake / stepping on the gas. Am I correct here? :confused:

You're basically correct.

I turn the engine off and engage neutral as soon as I suspect I'll have to stop. Coasting 500 feet won't damage your transmission, the warning is against extended coasting intervals w/ the engine off.

So basically, I hit the bottom of the shallow hill in town, and I can see the red light. It's about 300 feet further from where I can see it. I can tell based on where traffic is moving if I need to shut down or not. At 25MPH, I shut down the engine, coast up to the light, come to a stop. As the guy in front of me moves, I start 'er up and put 'er in gear. By the time the guy in front of me is a comfortable distance away, I can give Cara some pedal, and all's well on the home front.

Many of the townspeople think that my engine doesn't run right because it's always off at that light. They think that it stalls on it's own, because there is no indication that I've just shut it off while coasting.

I'm sure it would help my FE, but I'm not really comfortable EOCing in my car since it's an automatic. :( I was just wondering if shutting off and restarting once I'm already stopped would help at all.

If you have to shut off for only a few seconds, no.

Consider the small amount of fuel you use before the PCM enters closed loop mode again, before you get it back into gear, and while you're waiting for the transmission to be actively in gear. You have to defeat that much gas usage to make it worth while, versus the fuel used just idling for a few seconds. You're better off timing the lights, if you can, and preserving momentum as much as possible.

I read somewhere that the cutoff point for one person's car was something like 7.5 seconds of engine-off time to compensate for the fuel used in starting/taking off again. Anything more than 7.5 is black, anything less than 7.5 is red, for that person. I can't say for your car, and it does/will vary with your driving habits.

Sorry for being unclear... I meant shutting off the engine if there's like a minute-long or 30-second-long light or something. As far as my technique goes, whenever I see a red light, I take my foot off the gas and just coast up to it. I definitely need work on my red light anticipation, though.

If only most traffic lights had LED displays counting down seconds to change...
I've seen that in so different places in Europe, from Spain to Romania, and it is worth gold in my eyes. Unfortunately, Poland hasn't grown up to that yet :( But maybe lobbying the local officials will work?

That's a good start, though.

After awhile, you'll learn traffic patterns at each light, and be able to anticipate about how long it will be until the light changes. Sometimes, you'll find that it's actually better to use your brakes early on, slowing down enough to allow you to completely preserve the remaining momentum so that you're not starting off from a dead stop at the light.

The less speed you start from, the more energy you waste starting off, in a curved relationship.

IOW - The curve between starting at 0MPH and 10MPH is much steeper than the curve between 10MPH and 20MPH. More energy is wasted (especially in automatics) just getting the hulk of metal to move in the first place.

I am an unabashed automatic EOCer. I do just what Christ has suggested and it saves a bunch of fuel. More if you go alternatorless. Auto transmissions can be EOC'd safely for short distances. I have EOC'd for over 2KM every day for over a year with no problems (I have an extra vacuum canister for the brakes) It's impossible for the bearings to dry out over short distances with no load.

If you have to coast long distances get an electric pump installed for towing that turns on when you EOC.

I don't like to go further than a few hundred feet, but I have no evidence that supports damage for short distance coasting, either.

I've been looking into fish tank pumps for long distance EOC, but I don't think they'll flow enough volume to do anything really... I'm not going to invest too much time into it, either, because I don't plan on having an automagic for too much longer.

I don't even use a vacuum canister for my brakes, I just don't use the brakes if the engine is off, unless I absolutely have to. Often, I'm already going slow enough that I'm not going to run into anyone, but that's a function of learning your vehicle and local traffic patterns.

I do think that after my wife gets out of school, I'm literally going to start EOC the automatic as often as possible, just to see what it really takes to damage the transmission. Of course, that will be after I get something else ready to be put on the road, so that I won't have to go without a vehicle for more than a day or so.

I already coast up to red lights and stop signs at exit ramps. I love coasting off the highway.

My Yaris has DFCO, so I'm assuming that when I'm coasting up to stop lights, I'm not using any fuel until it gets down to a certain RPM, but I can't be certain. I guess I'll have to buy a ScanGauge and figure out how to use it.

I know much has been made on whether or not the car is 'flat-towable' or not. If it's flat-towable, supposedly you can EOC to your heart's content. If it's not flat-towable, that generally means that the transmissions parts don't get lubricated when the engine is off, and so there is usually some distance/speed limitation on coasting listed in the owner's manual. Even so, the occasional coast to a redlight is probably no big deal. After experimenting a little with it, I didn't see any significant fuel economy increase for my vehicles -- mostly, I think, because there were really only a couple of places in my usual commute where I felt comfortable doing it. (Besides, I like having power to the brakes and steering.)

Regarding the break-even point for fuel consumption, according to the BMW owner's manual, that point is reached after four seconds of idling. Now, that doesn't take into account additional wear and tear on the car for each additional startup, so take that with a grain of salt. My own rule of thumb is basically I'll let it idle for 20-30 seconds, but I will shut down if I know the wait will be longer AND if the engine is already at operating temperature AND if I haven't shut down within the last 5 minutes or so. (AND if Mrs. JKP1187 isn't in the car, too, because she'll no doubt want me to keep the HVAC running. :D)

I posted a thread a couple of months ago, Time Spent at traffic lights Engine off. I stop watched the amount of time that I had the engine off throughout the day. *Note - I drive an automatic, but do not EOC, I coast engine on, and I drive 150+ miles a day, different routes and roads. After 2 days of timekeeping and traffic light counting, with some math involved, I was engine off for about 20mins a day, about .25 of a Gal. 4 days = 1 Gal. of gas.

Try timing the amount your engine off drive is, and count the number of traffic lights you engined off for.

Oh hell, I can't do all that. I just turn the van off at random times when going down slight rolling hills and stuff, or when I can make a long coast to a stop sign...


(People hate me for the stop sign thing, by the way. Most everyone is used to slamming on the brakes as they approach the sign, I coast up to it gently, and I usually only have to brake from about 20 MPH by the time I get to the sign. I don't even re-start the van until I see a clear spot to pull out.)

Funny thing, too. I've had someone get mad enough at me to actually pull around in front of me while at a stop sign, shut their vehicle off, and come to me screaming their head off. This happened just a few weeks ago, actually.

So the guy comes up to Cara, and I always have a head-on attitude, so I unbuckle and get out before he gets there. I'm not an intimidating guy, so I rely on intelligence in most cases. This guy is yelling and screaming, and by the time I find a spot in his incessant rambling to actually say something, I calmly announce to him: "You're late."

"I'm late?! What the FSCK are you talking about?"

"I'm sure you were in a hurry to get somewhere, and my slow driving obviously upset you because you were in said hurry... and now, because you've stopped just to ramble on at me pointlessly, you're late."

All of a sudden, his face lightened up.. the scowl was gone, and he stopped yelling. He gave me a look of enlightenment, got back in his car, and left. I started Cara back up and drove up to the local Mickey Dick's to get some coffee.

Wow, calmness and intelligence FTW. :thumbup:

I would've just gone into reverse and gone around him. Lol.

I'm not that easy going. I've been known to scrap once and again.

That story is epic love it!

Well i guess i know what to say now if that ever happens to me =)

Christ, you are a god. That's hilarious and the perfect approach for the crazed lunatics who drive like there's fire in the back seat.

Lucky for me, people are so busy staring, pointing, taking pictures and laughing at my van, they don't even realize that I'm slowing them down.

Ever since I started driving with efficiency in mind, I am so much more relaxed behind the wheel. I love the silence of a still engine at a stop light.

Please, modesty... :P