Does idling waste fuel? - Engineering Explained
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My 3.5-litre six gets good to great fuel consumption on the highway. But in the city, especially during rush hour, it's abysmal compared to a Corolla I'm familiar with. (But that Corolla's consumption sucks big-time at highway speeds. It uses the same or more as my car at 100 to 110 kms per hour as it screams along. So I rationalize.)
With my car at ordinary red lights, the number to the right of the decimal point in the litres/100 kms average readout clicks up one to two decimal points. With longer red lights at more complicated intersections, it clicks up three times while just sitting.
This garden gnome (self-described) rants against stop-start, but Engineering Explained shoots him down with a couple of graduated cylinders and real data.
With my car at ordinary red lights, the number to the right of the decimal point in the litres/100 kms average readout clicks up one to two decimal points. With longer red lights at more complicated intersections, it clicks up three times while just sitting.
This garden gnome (self-described) rants against stop-start, but Engineering Explained shoots him down with a couple of graduated cylinders and real data.
Good video. Please make a point to turn off the engine after you pull into the bank's drive-through.
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
Originally Posted by irv
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
It happens here all the time. I think people if you calculate what you just waited idling you could have filled up down the street and not waited for the same cost.
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
It happens here all the time. I think people if you calculate what you just waited idling you could have filled up down the street and not waited for the same cost.
Originally Posted by irv
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
We can calculate how much gas they use (for a 1.5L engine):
10/60 x 0.63L/hour idling = 0.105 L x $1.3/L = $0.14
If you fill up 50 litres you save:
50 x $0.05 = $2.50
So you still save money idling for 10 minutes. If you use premium gas, which is 10 or 12 cents cheaper at Costco than other gas stations you save even more.
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
We can calculate how much gas they use (for a 1.5L engine):
10/60 x 0.63L/hour idling = 0.105 L x $1.3/L = $0.14
If you fill up 50 litres you save:
50 x $0.05 = $2.50
So you still save money idling for 10 minutes. If you use premium gas, which is 10 or 12 cents cheaper at Costco than other gas stations you save even more.
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Originally Posted by camrydriver111
Originally Posted by irv
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
We can calculate how much gas they use (for a 1.5L engine):
10/60 x 0.63L/hour idling = 0.105 L x $1.3/L = $0.14
If you fill up 50 litres you save:
50 x $0.05 = $2.50
So you still save money idling for 10 minutes. If you use premium gas, which is 10 or 12 cents cheaper at Costco than other gas stations you save even more.
Don't forget the yearly cash back as well.
Originally Posted by irv
I always get a kick out of those purchasing gas at Costco. Most go there because gas is usually 5 cents or more cheaper than most places but because of that, the line ups are usually huge so it can take 5-10 minutes sometime before one pulls up the pumps.
99% of the vehicles I see there are idling the whole time waiting to get filled up which is likely throwing any savings they are receiving buying this cheaper gas right out the window.
We can calculate how much gas they use (for a 1.5L engine):
10/60 x 0.63L/hour idling = 0.105 L x $1.3/L = $0.14
If you fill up 50 litres you save:
50 x $0.05 = $2.50
So you still save money idling for 10 minutes. If you use premium gas, which is 10 or 12 cents cheaper at Costco than other gas stations you save even more.
Don't forget the yearly cash back as well.
Interesting thread.
My Montero is hard on fuel while driving. Idling it barely uses any. It idles really low like 400 rpm and barely know it's running it's very smooth. I suppose if it sat all day not moving my mpg would go down but normal heavy bumper to bumper it excels at fuel mileage. No noticeable drop.
My other 2 cars use more fuel than the Montero at idle. In heavy city jams is when I really notice it. They can drop 20% or more in mpg.
Think there may be some generalizations for this but there are definitely exceptions as well.
My Montero is hard on fuel while driving. Idling it barely uses any. It idles really low like 400 rpm and barely know it's running it's very smooth. I suppose if it sat all day not moving my mpg would go down but normal heavy bumper to bumper it excels at fuel mileage. No noticeable drop.
My other 2 cars use more fuel than the Montero at idle. In heavy city jams is when I really notice it. They can drop 20% or more in mpg.
Think there may be some generalizations for this but there are definitely exceptions as well.
In the Chicago land area Costco prices for premium (which I use) is usually about 30-50 cents cheaper than normal gas stations. I have one that is about a mile from my house. It opens up at 6:30AM and I go there in the AM with no lines. I get 4% back from my Costco card too so it's not dumb to buy gas at Costco. Going on Saturday around noon is one way of guaranteeing yourself of having to wait.
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What I find strange is very few cars at idle consume such a small amount of fuel, my 3.8 Buick was about .44 gallons per hour the Dodge pickup is .8-1.2 gallons per hour at idle.
They should have picked a real world vehicle someone might actually own as opposed to an unpopular Toyota econobox sold outside the US
Originally Posted by PimTac
Originally Posted by camryrolla
Good video. Please make a point to turn off the engine after you pull into the bank's drive-through.
Good advice especially in Louisiana where air conditioning is not necessary.
[ sarcasm ]
My Insight would kill the engine coasting into the bank and believe it or not the fan blew cool air several minutes after the engine was dead.
They should have picked a real world vehicle someone might actually own as opposed to an unpopular Toyota econobox sold outside the US
Originally Posted by PimTac
Originally Posted by camryrolla
Good video. Please make a point to turn off the engine after you pull into the bank's drive-through.
Good advice especially in Louisiana where air conditioning is not necessary.
[ sarcasm ]
My Insight would kill the engine coasting into the bank and believe it or not the fan blew cool air several minutes after the engine was dead.
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My grandpa says that an idling engine should use about half the gas it would if cruising on the highway. Take it FWIW
I have a scan gauge so I have some data for different conditions with my car.
0.35 gph warm in neutral/park.
0.47 gph warm in gear.
0.65 gph warm in gear with aircon.
If I'm stopped at several lights on a trip, there's a significant fraction of a gallon burned just sitting. I don't turn off at normal red lights but at railroad crossings where I know I'll be there a while I'll shut down and save a bit. If brutally hot I'll put in neutral instead because every little bit helps.
0.35 gph warm in neutral/park.
0.47 gph warm in gear.
0.65 gph warm in gear with aircon.
If I'm stopped at several lights on a trip, there's a significant fraction of a gallon burned just sitting. I don't turn off at normal red lights but at railroad crossings where I know I'll be there a while I'll shut down and save a bit. If brutally hot I'll put in neutral instead because every little bit helps.
Originally Posted by Rmay635703
What I find strange is very few cars at idle consume such a small amount of fuel, my 3.8 Buick was about .44 gallons per hour the Dodge pickup is .8-1.2 gallons per hour at idle.
If you scale their number to your engine size it works out to about the same as your number.
3.8/1.5 x 0.63 L/h = 1.596 L/h / 3.785 = 0.42 gal/h
What I find strange is very few cars at idle consume such a small amount of fuel, my 3.8 Buick was about .44 gallons per hour the Dodge pickup is .8-1.2 gallons per hour at idle.
If you scale their number to your engine size it works out to about the same as your number.
3.8/1.5 x 0.63 L/h = 1.596 L/h / 3.785 = 0.42 gal/h
A couple of thoughts:
One is that I'd like to know how things scale in the real world according to displacement. Intuitively, it would make sense that it would scale linearly. With that said, a lot of small econobox engines idle at 800-1000 rpms while it's not uncommon for a big American V8 to idle at 600-650rpms or sometimes even slower.
With all of that said, I always think about my little MG with or really any carbureted car. The fuel "consumption" of a carburetor on a hot, stopped engine is not zero as some gasoline will always evaporate out of the float bowl. My MG(and most cars made up until the very early 1970s) is completely "open" and evaporated gas vents into the atmosphere. There are a lot of interesting things at play in this sort of situation, as in operation the constant atomization of gasoline in the carburetor throat keeps the temperature of the carbs relatively cool. In operation, a typical set of numbers might be 200ºF on the cylinder head, 150º at the intake manifold, 130º on the float bowl, and 120º in the throat. As soon as the engine is shut off, the intake and carburetors start to heat soak and in a minute or two will equilibrate out to probably 190º or better all over. If I shut the engine off in traffic, on restart(even after a minute or so) the fuel pump ticks a few times, signifying that the float bowls are probably down milliliter or two from full. Even more importantly, though, you end up with fuel in the throat of the carb(not sure if it's just simple fuel expansion or percolation, or a combination of both but whatever the case it happens) so the car runs EXTREMELY rich for several seconds on a hot restart and I suspect emissions(particularly CO and VOCs) are through the roof.
Carbureted vehicles don't really even enter into the big picture these days as there are not that many being driven these days and on the whole the ones that are driven tend to not rack up a lot of miles. I imagine that of the ones still racking up significant miles, vehicles without evaporative loss control systems are an even smaller portion(although that system doesn't fix fuel percolation and rich starts). Still, I'd like to know a "break even" point for a typical carbureted vehicle. I suspect it's a fair bit longer than the ~7s cited in this video, and maybe more like a minute or two. I doubt anyone will do the research, though.
One last thing-a few years back in my city there was a big campaign about being "idle free." The time used in all the advertisements was 10 seconds. It certainly made me conscious of shutting my engine off in drive throughs and places like that. I even do it in traffic(on surface streets, not interstates) provided it's not too obnoxiously hot or cold. I don't personally own/regularly drive a vehicle with start/stop(although my parents' current vehicles have them) so any start/stop is manual. The MG only gets turned off if I think it's going to be a couple of minutes. Funny enough, though, drivers of city-owned vehicles seem don't seem to follow the "ten second rule."
One is that I'd like to know how things scale in the real world according to displacement. Intuitively, it would make sense that it would scale linearly. With that said, a lot of small econobox engines idle at 800-1000 rpms while it's not uncommon for a big American V8 to idle at 600-650rpms or sometimes even slower.
With all of that said, I always think about my little MG with or really any carbureted car. The fuel "consumption" of a carburetor on a hot, stopped engine is not zero as some gasoline will always evaporate out of the float bowl. My MG(and most cars made up until the very early 1970s) is completely "open" and evaporated gas vents into the atmosphere. There are a lot of interesting things at play in this sort of situation, as in operation the constant atomization of gasoline in the carburetor throat keeps the temperature of the carbs relatively cool. In operation, a typical set of numbers might be 200ºF on the cylinder head, 150º at the intake manifold, 130º on the float bowl, and 120º in the throat. As soon as the engine is shut off, the intake and carburetors start to heat soak and in a minute or two will equilibrate out to probably 190º or better all over. If I shut the engine off in traffic, on restart(even after a minute or so) the fuel pump ticks a few times, signifying that the float bowls are probably down milliliter or two from full. Even more importantly, though, you end up with fuel in the throat of the carb(not sure if it's just simple fuel expansion or percolation, or a combination of both but whatever the case it happens) so the car runs EXTREMELY rich for several seconds on a hot restart and I suspect emissions(particularly CO and VOCs) are through the roof.
Carbureted vehicles don't really even enter into the big picture these days as there are not that many being driven these days and on the whole the ones that are driven tend to not rack up a lot of miles. I imagine that of the ones still racking up significant miles, vehicles without evaporative loss control systems are an even smaller portion(although that system doesn't fix fuel percolation and rich starts). Still, I'd like to know a "break even" point for a typical carbureted vehicle. I suspect it's a fair bit longer than the ~7s cited in this video, and maybe more like a minute or two. I doubt anyone will do the research, though.
One last thing-a few years back in my city there was a big campaign about being "idle free." The time used in all the advertisements was 10 seconds. It certainly made me conscious of shutting my engine off in drive throughs and places like that. I even do it in traffic(on surface streets, not interstates) provided it's not too obnoxiously hot or cold. I don't personally own/regularly drive a vehicle with start/stop(although my parents' current vehicles have them) so any start/stop is manual. The MG only gets turned off if I think it's going to be a couple of minutes. Funny enough, though, drivers of city-owned vehicles seem don't seem to follow the "ten second rule."
My TDI seemed to burn nothing at idle. Major pain in winter if it was iced over. I'd scrape what I could but it sure would have been nice to have heat on some occasions, like after ice storms.
Just read that the starter on my truck is a pain to replace (major job) so I'm starting to let that idle more when I go places, if it's just a few minutes then it'll idle.
I rarely use drive through though. It's strange, I don't mind sitting around as long as I'm moving... but sitting in traffic (or a drive-thro) drives me nuts. I'd rather go inside and stand in line. I guess I could always pull out my smartphone and surf the web.
Most places I go don't have drive thro anyhow.
Just read that the starter on my truck is a pain to replace (major job) so I'm starting to let that idle more when I go places, if it's just a few minutes then it'll idle.
I rarely use drive through though. It's strange, I don't mind sitting around as long as I'm moving... but sitting in traffic (or a drive-thro) drives me nuts. I'd rather go inside and stand in line. I guess I could always pull out my smartphone and surf the web.
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