--- MPG Gain With Engine off at Stoplights? ---
 

I Am not talking about EOC, since i have an automatic, just turning off the engine at stop lights instead of leaving it idling...

Anyone has any mpg gains by doing this? ...I am trying to see if it really is worth it; If i gain only 1mpg I wount go through the trouble but if its something like 3-4mpg then of course...

Driving patterns.
 

Depends a lot on your driving patterns and how much fuel you burn just sitting there at idle. The Blue BAT burns 0.6 gallons per hour stopped, idle, in gear. I can end up spending 15 minutes waiting at lights in a 20 mile urban drive. Let's say I get 20 mpg while in motion. I would burn 1.15 gallons with engine on at lights or 1 gallon with engine off. That is the difference between 20 mpg and 17.4 mpg.

Actually I just tested this. Idling at stops was %17 of my fuel in the test. Every car/driver/route will be different of course, so I added tracking of fuel spent at 0mph to the guino:
http://ecomodder.com/forum/showthrea...ting-5144.html

In typical city driving, you use at least 10%-15% of your fuel idling. I read a research paper that quoted a city EPA figure of 17%, though the exact driving cycle was not specified (see zero inertia powertrain)

Turning the engine off at lights, especially ones you know are long is certainly worth it if you tend to do a lot of urban/city driving. You can EonC in an automatic, I do it all the time with my Monte Carlo. It helps if the gear shift is on the floor, but you can still do it if it's on the steering column. Simply shift into neutral (if the gear shift is on the floor you can go between neutral and drive without pushing the button. Coast up to the stop and with the brake applied just shift back into drive. You can usually shift into drive without the brake, but this depends on each individual vehicle.

I don't know about gaining, but I watch my "current" MPG drop off while I am idling. I suppose that any time you are not moving and not using gas, that would be an MPG gain, vice idling and not moving.

The rest of your question - I lose about 1/2 mpg max idling over 30 seconds - depending on how far I have traveled on that trip. The less time it has been since I started the trip the more MPG loss.

On a typical drive in my town, I've measured about a 15% difference.

off on
 

July 1980 Popular Science,page 70:"Stop-go fuel saver",by Zemco Corp.,San Ramon,California.Tested on EPA Urban Cycle,the device(which does as you describe) improves mpg by 7.5%.

Once I get my MPGuino calibrated, I'll test how much fuel I use idling and try to remember to post back. :)

One thing I wonder about shutting the engine off is... does the computer go into open loop or does it run a little rich on startup? Or is that only on a cold start.

Hiya,

I have been doing this more often now, especially if I can see the lights in the other direction change to yellow (if I am at the head of the line); or I wait until the vehicle 2 or 3 ahead of me starts to move, and then I start it up again.

I look at it more from the stand point that it doesn't hurt my FE, that I have worked so hard to maintain.

Another thing I have started doing is pulsing at the top of a hill to start my glide at a higher speed. If you do this right, it gains more than it loses.

I could double check with the scangauge but I'm pretty sure if it is warm it would stay in closed loop.

To the original question, regardless of the savings, why wouldn't you shut the engine off when it is not needed? I always kill it at red lights, try to watch the opposite light to see when my green is coming, and on lights I hit all the time I even count off in my head how long they take to change so I can fire it up with just a second or two to spare. Hardly too much effort to make on behalf of the planet and my wallet.

Well all I wonder is starter wear... because on a typical city drive I could turn off my car probably 10 times instead of just once (when I first turn on the car)...

re: starter, I think DAOX responded to this question in another thread, but IIRC the most notorious hypermiler using an automatic got 80,000 out of his starter.

Folks are spending hundreds per year idling, that will likely go up.

A starter for your 07 car is less than $200 from autozone. A starter for my car is $75, without any shopping around. My annual fuel costs for idling are somewhere around $150.

So if in my scenario, I would have to replace starters twice a year to lose money on the deal. My starter should last 16 years, since I bump start half the time.

The break even point is somewhere around a year on average for parts if I had to guess. Labor costs is at your discretion, at it's essence it is removing two bolts and two terminals, though some starters ARE a pain to get to. I don't mean the "I don't feel like getting my hands dirty" pain, but like you have to take off the intake manifold pain. Ah well, just more bolts :)

I believe it was closer to 95,000 miles that Wayne got on his starter.

My civic goes to Closed Loop immediately, within one update cycle. That's with the scangauge set on Fast refresh, too.

Yea, I hear ya. I like being at least a few cars back from the light. Although I can't see the light going the other way, I have time to start and move before the traffic ahead of me moves.

Do you think that the additional alternator load on recharge of the battery after restart will negate the fuel saved while the engine is shut off?

No. I see a 20% or more gain by shutting it off at stops. The alternator load is minimal compared to fuel used for idling.

Just an update re: open/closed loop. I checked today and sure enough it stays in open loop for about 15-20 seconds after startup even when warm. I'm still inclined to think that the increased fuel burned in that period due to open loop is less then the fuel saved by not idling at the light. This would be very hard to quantify though.

But, if I understand your post correctly, that would depend on how long you would be idling...I think. I usually turn my motor off if I know I'm going to be sitting for longer than 30 seconds. Less than that, I just idle. Once I get the 'guino calibrated, I'll have to try and get some semi-exact numbers to back up the theory.

My starter has at least 150,000 miles on it, so I'm leaving the engine running (except waiting at the drive-thru, railroad crossings, etc.) When I next have to replace my starter, I'll start keying off then.

This afternoon, I had to wait for a long train to pass at a train crossing and I switched the car off until I saw the end of the train coming near. Don't know if I have saved anything.
I did worry that if someone failed to see the need to stop and come behind me too closely for comfort, I might not have instant power to move the car forward a few feet. Chances of this happening should be slim anyway.
I am also curious about the legality of doing this. My intuition says that it is OK. I think it is a good way to reduce emissions and hence should be made legal. However, as in many other circumstances, I think for safety, the driver should do this only when the relevant situation permits.

I can't imagine why it would be illegal. I actually did it in front of a cop once. Don't think he/she even noticed.

Thanks! I feel reassured. I will probably do it again when I meet another train at a train crossing.
To me, it stands to reason that this practice should save some fuel and reduce some emissions.