fuel used idling vs restarting

[dcb]

I did a little experiment today with the mpguino.

I drove to work, but anytime I was stopped I left the engine running. I did my usual EOC, but would bump start it at the last second so I would never have to hit the starter.

I noted my idle gallons, it was 0.07 gallons, out of a total of 0.41 gallons.

The ride home I eoc'd and did not idle at all. idle gallons was 0.00 (out of 0.33 gallons), even though I used the starter several times while sitting perfectly still.

I usually get about the same mileage to and from work so no huge variance there. but I used significantly more fuel when leaving the motor running than just using the starter when necessary. Using the starter didn't even register whereas idling took %17 more fuel on my particular car/route/driving style.

For my car/commute that would mean (@4$/gallon) I would be spending roughly $140 per year on idling if I chose to. That is like 1/10 of what I paid for the car

[modmonster]

wow that awsome! i was wondering about how much ideling was costing me. did you have lots of stationary traffic? i think i saw a calculation for idle gallons per hour on this site that was more conservative than your data suggests. what vehicle were you driving?

[dcb]

It was a 3cyl metro. Working backwards, I must have spent about 12 minutes sitting still, which is a lot more time than I would have guessed. I Guess it adds up.

[Daox]

Thanks for the info dcb! Wow, that does seem like a long time to site idling. It just proves the point furthere that shutting the engine down at lights is an easy way to make good gains if your doing a lot of city driving.

[ptsmith24]

Thanks for posting those results. I drive an automatic, so I'm still not sold on the idea of EOC in it. However, I know how many of the lights are timed around my town, so I kill the motor once I come to a stop. I do more driving at 55mph than I do at city speeds in terms of miles driven, though. But, any gain is any gain in my book.

[Doofus McFancypants]

i pondered driving with a stop watch to time the ammount of Idle time there is on an average commute. Just never remember to grab the watch before i walk out the door.

my 2.5l 4-cyc idles at about 0.25 gal / hr. and a typical commute in uses about 0.4 total gallons. 10 minutes of idle would be an additional .04 gallons.

that is 10% of my fuel going to making heat!!

i had not figured how to calc the Key start fuel - but as soon as the car is on i am moving so i considered it pretty small.

Steve

[SVOboy]

Sweet! I've been wanting to do a test like this for ages, but I've always been an idler, though recently (mpguino encouraged), I've been keying off more when sitting at lights and such.

[saunders1313]

Originally Posted by ptsmith24

Thanks for posting those results. I drive an automatic, so I'm still not sold on the idea of EOC in it.

Don't be afraid to EOC, depending on what EOC you're talking about, engine on coasting or engine off coasting. I engine on coast all the time in my automatic. Just shift it into neutral and when you want to get back into gear either rev the engine up to the rpms it should be or hit the brake (lightly) and shift into gear then let go of the brake. Even if you just coast with the engine on instead of off you'll save fuel instead of using the brakes a lot.

[MetroMPG]

Originally Posted by modmonster

i think i saw a calculation for idle gallons per hour on this site that was more conservative than your data suggests.

You probably saw this: How much fuel does it take to re-start a warm engine?

Nice work, dcb.

[ptsmith24]

Originally Posted by saunders1313

Don't be afraid to EOC, depending on what EOC you're talking about, engine on coasting or engine off coasting. I engine on coast all the time in my automatic. Just shift it into neutral and when you want to get back into gear either rev the engine up to the rpms it should be or hit the brake (lightly) and shift into gear then let go of the brake. Even if you just coast with the engine on instead of off you'll save fuel instead of using the brakes a lot.

Engine Off Coasting. I already cost in N with the engine on and then turn the engine off at longer lights. Even when I'm coasting in neutral to, say, a 45 mph zone from a 55 mph zone, I don't have to do anything but 55 > N > 45 > D, no gas/brake deal you're talking about. No adverse affects thus far and no symptoms of anything bad. I don't do that much, but I definitely try to time out lights by N-coasting towards them. Right now, I have a little over half a tank left and I've been about 230-240 miles. I'm staying under 60MPH (mostly close to 55MPH) for this tank to see how much more that helps my mileage over the last tank on which I did 45 miles or so at 65-70MPH. Once my mileage levels off at 55MPH driving, I'll look into doing a little more each tank. I don't want to change too many things each tank because if FE gets worse, it would be more difficult to determine the exact cause. I know that isn't likely with the tips on this site, but that's the way I want to do it.