# Car Idling 'Factoids' - contradictory? **URL:** \ **Category:** Factual Questions\ **Created:** [March 19, 2010, 4:37pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029 "2010-03-19T16:37:28Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [March 19, 2010, 4:37pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/1 "2010-03-19T16:37:28Z")
Our company sent out a ‘green tip’ this morning all about car engines and idling. These two factoids were right together: One hour of idling burns up to a gallon of fuel. An idling vehicle emits 20x more pollution than one travelling 32 mph. I don’t see how both could be true (except in the case of a car that gets 640 mpg, so the car traveling 32 mph would use 1/20 gallon in an hour). Is this just idiocy? Or am I missing something? If we didn’t count carbon dioxide as ‘pollution’ would that make a difference (I’m assuming the water produced by burning gas is pretty constant no matter the efficiency of the engine, so it wouldn’t matter if you called water ‘pollution’ or not)? ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [March 19, 2010, 5:00pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/2 "2010-03-19T17:00:41Z")
My guess is it should have read ‘An idling vehicle emits 20x more pollution **per gallon of fuel** than one traveling 32 mph.’ ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [March 19, 2010, 5:01pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/3 "2010-03-19T17:01:07Z")
> [@bup](#): > > An idling vehicle emits 20x more pollution than one travelling 32 mph. I’m having trouble seeing how this could be true, or even close to it. A car going 32 mph (unless it’s coasting downhill) is running its engine at greater than idle speed and necessarily using more fuel per minute than one that is idling. With modern systems that are designed to maximize efficiency under all conditions, I don’t see how the idling engine is going to produce more pollution, much less twenty :eek: times more. Now, if they’re trying to talk about how much pollution per mile, the idling vehicle emits infinitely more than any moving vehicle, the point being long periods of idling are not eco-friendly. But still the “20x” figure is inane. Sure doesn’t make sense to me. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [March 19, 2010, 5:02pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/4 "2010-03-19T17:02:31Z")
> [@bup](#): > > One hour of idling burns up to a gallon of fuel. I can tell you that for most cars, certainly most cars sold in the last 25 years, this is a little high. A typical rate for a decent-sized engine is more like half a gallon or less per hour. But then, if this message is aimed at people driving delivery-type vehicles like big vans, maybe it’s close. > [@bup](#): > > An idling vehicle emits 20x more pollution than one travelling 32 mph. This is true in the sense of there’s a higher concentration of pollutants when your car is idling, but then it’s emitting far less exhaust. This is especially true for prolonged idling (like 5 minutes or more) in which case the catalytic converter can cool down and stop functioning efficiently. Another thing to keep in mind is that the engine on a modern car cruising at 32 mph is probably not turning much faster than idle, so that particular factoid should not be particularly shocking. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [March 19, 2010, 5:06pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/5 "2010-03-19T17:06:22Z")
> [@bup](#): > > One hour of idling burns up to a gallon of fuel. heh. I visited a friend last week. I did not intend to do more than return a book and then leave, so I left my car running. I accepted an offer of a beer, next thing I know 3 hours had gone by. I was shocked by how little gas had been used. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [March 19, 2010, 5:14pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/6 "2010-03-19T17:14:17Z")
> [@GreasyJack](#): > > there’s a higher concentration of pollutants when your car is idling What does that mean? Does it mean that burning the same amount of octane in an idling engine produces relatively more carbon-monoxide (or whatever other partially burned compounds burning gas can create), and relatively less pure carbon-dioxide? ---
**Author:** ![Gary\_Robson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gary_robson/32/3448_2.png) [@Gary\_Robson](https://boards.straightdope.com/u/Gary_Robson)\ **Post date:** [March 19, 2010, 6:14pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/7 "2010-03-19T18:14:29Z")
I think that’s the crux of the matter, **bup**. The definition of “pollutant.” Is CO a pollutant? How about CO[sub]2[/sub]? Or just particulate matter? You can always tweak definitions to make factoids sound worse (or better) than they really are. ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [March 19, 2010, 6:22pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/8 "2010-03-19T18:22:13Z")
> [@bup](#): > > Our company sent out a ‘green tip’ this morning all about car engines and idling. > > These two factoids were right together: > > One hour of idling burns up to a gallon of fuel. > SNIP I call bull on one gallon at idle on anything short of a locomotive. I’ve attached a Scangauge II OBD monitor to several vehicles. A 200 HP V6 I monitored only burned 0.4 with the AC on high and 0.3 without the AC. Double that engine size and you’re still under 1 gallon. The only way you’d get to 1 GPH burn rate is if you had a police car, fire truck or ambulance and activated the “high idle switch” to run high RPM in order to drive lights, ladders, pumps or medical equipment without draining the battery. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [March 19, 2010, 6:27pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/9 "2010-03-19T18:27:48Z")
Yeah, drive for an hour at 30 MPH in a car that gets 30 mpg and then you burn a gallon… DRIVING. The am’t of energy to drive at 30 MPH is enormous compared to an idling engine. At idle? Maybe a pint or two. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [March 19, 2010, 6:31pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/10 "2010-03-19T18:31:12Z")
> [@bup](#): > > Our company sent out a ‘green tip’ this morning all about car engines and idling. > > ? How did they send out that tip? ---
**Author:** ![Lanzy](https://avatars.discourse-cdn.com/v4/letter/l/74df32/32.png) [@Lanzy](https://boards.straightdope.com/u/Lanzy)\ **Post date:** [March 19, 2010, 6:37pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/11 "2010-03-19T18:37:02Z")
> [@Philster](#): > > How did they send out that tip? They went building to building handing out flers while leaving their car idleing outside.😃 ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [March 19, 2010, 6:41pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/12 "2010-03-19T18:41:20Z")
> [@Lanzy](#): > > They went building to building handing out flers while leaving their car idleing outside.😃 Perhaps a large truck with a billboard on it outlining these facts that repeatedly circled the building until the staff got the message? Seriously, I bitched at their stat, but if traffic is light I’ve been known to cut off my engine at stoplights. I like the general idea. ---
**Author:** ![EmAnJ](https://avatars.discourse-cdn.com/v4/letter/e/d2c977/32.png) [@EmAnJ](https://boards.straightdope.com/u/EmAnJ)\ **Post date:** [March 19, 2010, 7:53pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/13 "2010-03-19T19:53:17Z")
While I don’t think those facts are correct, I do think that idling if you don’t need to is a bad idea. It’s not just the emissions, it’s the cumulative effect of all those cars idling and using up our limited supply of fossil fuels. Yeah, yeah, we have a few billion barrels left, and I’m sure most people don’t really care about pollution in the first place, but it’s still billions of dollars of lost product. In addition to that, it’s about air quality too. Kids are especially susceptible to poor air quality. Think of the children! ---
**Author:** ![EmAnJ](https://avatars.discourse-cdn.com/v4/letter/e/d2c977/32.png) [@EmAnJ](https://boards.straightdope.com/u/EmAnJ)\ **Post date:** [March 19, 2010, 7:56pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/14 "2010-03-19T19:56:19Z")
Here is a link that says that idling 10 minutes a day consumes 100 L of gas a year: [Idling Factsheet - Ontario](http://air.greenventure.ca/webfm_send/16). I’m sure that doesn’t compare to the 1 gallon and hour at all. ---
**Author:** ![constanze](https://avatars.discourse-cdn.com/v4/letter/c/f9ae1b/32.png) [@constanze](https://boards.straightdope.com/u/constanze)\ **Post date:** [March 19, 2010, 8:26pm UTC](https://boards.straightdope.com/t/car-idling-factoids-contradictory/533029/15 "2010-03-19T20:26:03Z")
While I can’t find figures in a quick google-search, all - the ADAC (drivers association), the lawmakers, the auto experts and the nature groups - in Germany agree that letting your car idles is very harmful to the enviroment. The usual situations are: letting the car idle to “warm up the engine” in winter. This is unneccessary to harmful (the engine warms up through driving moderatly) and punished with a fine. Experts say (though the exact figures will vary from car type to type and with year of build) that when the engine is cold and idling that the combustion process is incomplete and ineffecient compared to normal driving speed, and that’s why the pollution is higher. Driving in traffic and stopping at a red light, train crossing or similar for longer than 1 minute. Again, recommendations across the board are to stop the engine to save on pollution. Some particularly long crossings have signs to turn the engine off. And some new cars have a start-stop automatic inbuilt that cuts the engine smoothly when the car is moving slow or standing.