Idling and fuel consumption

Joined
Jun 4, 2005
Messages
971
Location
Boston
Heavy truck diesels (800 cu. in. range} use .45 gals/hour idling, smaller pick-up sized diesele slightly less. Your average auto gas engine would consume about .5 gals/hour because it idles higher.
 
Joined
May 12, 2005
Messages
2,698
Location
Silicon Valley
A tiny mind (mine) experiment would suggest 1/2 gallon per hour at idle is way too high for a car. If my car gets 30 MPG at 60 MPH, thats 2 gallons per hour. I would estimate that just idling would consume a twentieth of that at most, so less than a tenth of a gallon per hour at most. YMMV.
 
Joined
May 7, 2004
Messages
10,910
Location
Nokesville, VA
The Scangauge says my 2.5L V6 1996 Ford Contour consumes .2 GPH at idle with the air conditioning off. It's EPA rated at 31MPG highway.
 
Joined
Mar 31, 2003
Messages
418
Location
OR
Interesting thread. Gas has never been higher yet I rarely see people, except myself, turning off the car at a railroad crossing waiting for the train or while stopped in a construction zone. People just idle away at 0 mpg. UPS must have the largest vehicle fleet in the world and they've learned that shutting off the truck even for a minute or two saves $'s. I also see diesel truck stops and they never shut those things off even for hours at a time. It doesn't make any sense.
 
Joined
May 7, 2004
Messages
10,910
Location
Nokesville, VA
quote:
Originally posted by davefr: Gas has never been higher yet I rarely see people, except myself, turning off the car at a railroad crossing waiting for the train or while stopped in a construction zone. People just idle away at 0 mpg.
My mom used to do that years ago (probably still does, though there's not many RR crossings where she lives now). I don't really see any good reason not to do it unless you're driving such a piece of junk that it might not restart.
 
Joined
May 12, 2005
Messages
2,698
Location
Silicon Valley
Not to open a can of worms, but I'd rather save my starter motor and battery than save drops of gas. One could also argue that re-starting a car releases more unburned fuel and pollutants than just leaving it running, but of course that depends on a lot of factors, especially the time spent idling. At $3 per gallon of fuel and 0.2 gph idling consumption, a 10 minute idle burns 10 cents of fuel. (Not that I would idle for 10 minutes, but I reckon I'd idle for 5 minutes, depending on the circumstances.) I'm disappointed that a car should consume 10% of its 60 MPH consumption just idling, which is what 0.2gph works out as. It's likely that UPS shuts off their trucks during deliveries more for insurance and legal reasons than actual gas and money saving reasons. [ August 30, 2005, 03:04 PM: Message edited by: Tosh ]
 
Joined
May 7, 2004
Messages
10,910
Location
Nokesville, VA
quote:
Originally posted by Tosh: One could also argue that re-starting a car releases more unburned fuel and pollutants than just leaving it running, but of course that depends on a lot of factors, especially the time spent idling.
One would have to take into account, of course, the fact that most pollution and unburned fuel gets released during a cold startup, which is not the case if the engine has only been shut off for a few minutes. As far as idling for 10 minutes, at the RR crossings we have in this town that's a very real possibility. More than once I've seen these stupid trains with the locomotive half-blocking a RR crossing, and to give you an idea Norfolk Southern operates, sometimes they just up-and-fail: gates down, lights flashing, no train coming. One can draw some conclusions about their attitude towards preventative maintenance from that. EDIT: A lot of the delay is due the a sharp curve in the tracks southwest of downtown Manassas, for which trains have to slow to 10MPH. [ August 30, 2005, 05:45 PM: Message edited by: brianl703 ]
 
Joined
May 7, 2004
Messages
10,910
Location
Nokesville, VA
By the way, I've done a Google search and the most commonly quoted figure for the amount of gas a car uses at idle is between 1/2 and 1 gallon per hour.
 
Joined
Sep 28, 2004
Messages
113
Location
Erie,PA
Mine shuts off at all stop lights and rr crossings all by itself! Even shuts off going down hill. Must be how it gets 50+ mpg. [Smile]
 
Joined
Jun 22, 2004
Messages
1,779
Location
Central Iowa
quote:
Originally posted by Tosh: Not to open a can of worms, but I'd rather save my starter motor and battery than save drops of gas. One could also argue that re-starting a car releases more unburned fuel and pollutants than just leaving it running, but of course that depends on a lot of factors, especially the time spent idling. At $3 per gallon of fuel and 0.2 gph idling consumption, a 10 minute idle burns 10 cents of fuel. (Not that I would idle for 10 minutes, but I reckon I'd idle for 5 minutes, depending on the circumstances.) I'm disappointed that a car should consume 10% of its 60 MPH consumption just idling, which is what 0.2gph works out as. It's likely that UPS shuts off their trucks during deliveries more for insurance and legal reasons than actual gas and money saving reasons.
UPS shuts their trucks off to save fuel. Back in the early 90's when I worked for an LTL carrier we did the same thing. Drivers were required to turn the trucks off anytime they were stopped. The starters are built heavy enough that replacing one was a rare event, and only happened in some of the older city units that were near the end of service anyway.
 
Joined
May 12, 2005
Messages
2,698
Location
Silicon Valley
I'm not saying they weren't also saving fuel by shutting the trucks off. I'm suggesting that it is likely illegal as well as a huge liability to leave a running vehicle unattended, and that this was their primary concern.
 
Joined
May 12, 2005
Messages
2,698
Location
Silicon Valley
quote:
Originally posted by brianl703: By the way, I've done a Google search and the most commonly quoted figure for the amount of gas a car uses at idle is between 1/2 and 1 gallon per hour.
'Commonly quoted' doesn't necessarily mean accurate. Are you backing out of the original 0.2 gph claim as seen on your Scanguage? The Google search I did turned up this page (from India): http://www.pcra.org/transport/CRRIstudy.htm The 'Ambassador' vehicle idles at 0.21 gph (in 1982). Presumably it had a V8. The Premier Padmini (a 50s Fiat-licensed 1100cc carburated engine) idles at 0.13 gph (1996). I would hope a modern fuel injected car could do better than either of those. Perhaps somewhere else there will be evidence of something more applicable.
 
Joined
May 7, 2004
Messages
10,910
Location
Nokesville, VA
quote:
Originally posted by Tosh: 'Commonly quoted' doesn't necessarily mean accurate. Are you backing out of the original 0.2 gph claim as seen on your Scanguage?
No. You are saying it should be lower...everything I've seen indicates that it should be higher. Perhaps the Scanguage is correct, and it really is .2gph. The people who make the Scanguage say that it's accuracy is plus/minus 5% to 10%, which vehicles having "calibrated sensors" being more accurate than those without out. They didn't specify what "calibrated sensors" are, but I suspect they mean vehicles that use a MAF instead of a MAP sensor to determine the amount of air entering the engine. My vehicle has a MAF sensor. When considering how much fuel a vehicle uses at idle, it might help to consider that gasoline engines are not very efficient at light loads. Idle is almost no load.
 
Top