# For better MPG, shift to neutral or leave in gear? **URL:** \ **Category:** Factual Questions\ **Created:** [April 10, 2013, 1:06pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320 "2013-04-10T13:06:42Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [April 10, 2013, 3:22pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/21 "2013-04-10T15:22:19Z")
> [@Colophon](#): > > Anecdotally, my car disagrees with you. There’s a roughly half-mile hill down towards my house, and I have experimented with taking my foot off the gas, and also putting the clutch to the floor (which is functionally the same as shifting to neutral). > > The instant MPG readout, which on my car will only display up to a max of 199mpg before showing “----”, typically shows around 150mpg with the clutch to the floor and/or the gear lever in neutral, but “----” (i.e. over 200mpg) if I leave it in gear and just coast down the hill with no gas. > > Edit: Here’s a post I made on this very issue 18 months ago: [Why does my car use more fuel coasting in neutral than when in gear? - Factual Questions - Straight Dope Message Board](http://boards.straightdope.com/sdmb/showthread.php?t=626533) > > Explained by **Ludovic** thus: > > which makes sense to me. My 2006 Jetta is the same – it’s difficult to get to “—” in neutral (impossible, if the AC is on), but if you take your foot off the gas on a hill, it goes to “—” immediately, indicating that the gas has been shut off. This is also true when just coming to a stop – I see a lot of manual drivers putting their foot on the brake and the clutch at the same time, but if you just assist the engine braking with your actual brakes, you should get better mileage (I’m not starting an argument over downshifting!). It’s all going to depend on the hill, what speed you want to be at at the bottom, AC on or off, etc. But, when you’re actually on the hill itself, my car will use less (that is, no) gas when you leave it in gear than if you put it in neutral. ---
**Author:** ![Lukeinva](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lukeinva/32/17872_2.png) [@Lukeinva](https://boards.straightdope.com/u/Lukeinva)\ **Post date:** [April 10, 2013, 4:17pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/22 "2013-04-10T16:17:39Z")
My German driving teacher would never allow coasting in neutral, for safety reasons. You have much less control of your vehicle in neutral. ---
**Author:** ![chargerrich](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chargerrich/32/5399_2.png) [@chargerrich](https://boards.straightdope.com/u/chargerrich)\ **Post date:** [April 10, 2013, 4:26pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/23 "2013-04-10T16:26:04Z")
> [@Xema](#): > > I have an aftermarket device (the [ScanGauge](http://www.scangauge.com/)) on my 1999 Ford E-150 van that displays fuel flow and confirms that when descending a sufficiently steep hill, fuel consumption goes to zero. > > So I think it’s reasonable to assume that this is normal even in older vehicles. > Right. And the energy used by the engine can come from the gravitational potential energy of a vehicle on a hill - it need not necessarily come from burning fuel. Really not trying to be combative here, but I do not see how it would be possible to have any car that runs on fuel only (hybrids and electric excluded) and has an INTERNAL COMBUSTION engine that is RUNNING to not be burning some amount of fuel. A combustion engine requires fuel to be delivered into the cylinder for ignition and compression to move the pistons. If the ECU cuts off fuel, then the engine is not active. While I am aware that some newer cars do this at every stop - and that is great - lets clarify that this is the not the norm for most cars. If we are talking about the motor being off then sure no fuel is being used, but I feel that is not the point of question from the OP. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [April 10, 2013, 4:28pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/24 "2013-04-10T16:28:05Z")
> [@JerrySTL](#): > > Many new cars will cut off the gas when coasting in gear once the engine is fully warmed up. If you put it in neutral, then the engine requires fuel to maintain idle or it would stall out. Agreed, except for the “many” and “new” parts. Except for a few of the very earliest systems, virtually every car with electronic fuel injection shuts off fuel supply when coasting in gear. That means pretty much any car sold since the late 80’s or so. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [April 10, 2013, 4:33pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/25 "2013-04-10T16:33:47Z")
> [@chargerrich](#): > > Really not trying to be combative here, but I do not see how it would be possible to have any car that runs on fuel only (hybrids and electric excluded) and has an INTERNAL COMBUSTION engine that is RUNNING to not be burning some amount of fuel. > > A combustion engine requires fuel to be delivered into the cylinder for ignition and compression to move the pistons. > > If the ECU cuts off fuel, then the engine is not active. While I am aware that some newer cars do this at every stop - and that is great - lets clarify that this is the not the norm for most cars. If we are talking about the motor being off then sure no fuel is being used, but I feel that is not the point of question from the OP. I suppose you can make some academic point about whether the engine is really “running” if it’s just being turned by the car’s inertia, but you’re completely wrong about this not being the norm for most cars. It has been for at least two decades. The driver doesn’t really notice since all the belt driven accessories are still turning and the engine can start producing power again instantly. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [April 10, 2013, 4:33pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/26 "2013-04-10T16:33:48Z")
> [@chargerrich](#): > > A combustion engine requires fuel to be delivered into the cylinder for ignition and compression to move the pistons. It’s a two-way mechanical thing. Engine burns fuel and turns a crank that sends power to the wheels (transmission omitted); and when gravity is pulling the car down the hill the rolling wheels turn the crank in the engine. Imagine being on a bicycle that doesn’t let you coast. Normally, yeah–you gotta expend some energy to work the pedals. But riding such a contraption down hill, well, the pedals work you–your legs will keep moving but you’re expending no energy in the process. But does this work even with an automatic transmission? ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [April 10, 2013, 4:34pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/27 "2013-04-10T16:34:19Z")
> [@chargerrich](#): > > Really not trying to be combative here, but I do not see how it would be possible to have any car that runs on fuel only (hybrids and electric excluded) and has an INTERNAL COMBUSTION engine that is RUNNING to not be burning some amount of fuel. > > A combustion engine requires fuel to be delivered into the cylinder for ignition and compression to move the pistons. > > If the ECU cuts off fuel, then the engine is not active. While I am aware that some newer cars do this at every stop - and that is great - lets clarify that this is the not the norm for most cars. If we are talking about the motor being off then sure no fuel is being used, but I feel that is not the point of question from the OP. It’s called deceleration fuel cutoff. You can search for DFCO to see it discussed elsewhere. If that’s not what’s happening, then explain this: Going downhill in my car, AC is on, put car in neutral – MPG gauge reads, say 130 MPG. Going downhill in my car, AC is on, leave car in gear and take foot off gas – MPG gauge immediately goes to “—”, basically, off the charts. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [April 10, 2013, 4:35pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/28 "2013-04-10T16:35:51Z")
Does this all apply to automatics as well? Better mileage-wise to take my foot off the gas than to shift it into neutral? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 10, 2013, 4:35pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/29 "2013-04-10T16:35:20Z")
> [@Xema](#): > > The trick is to shift into neutral as you approach the bottom of the hill, such that you reach the maximum safe speed at the bottom and thus climb the next hill with the least expenditure of fuel. Unless we’re talking about enormous long hills, or very steep ones, or low speed limits, that shift point is often nowhere near the bottom of the hill (and may in fact be right at the top). Because if you have engine-braked all the way down, your car isn’t suddenly going to make up speed on the last little bit of downhill slope. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [April 10, 2013, 4:37pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/30 "2013-04-10T16:37:21Z")
Although it has nothing to do with the pros and cons of coasting in neutral as far as MPG goes, it is illegal to do so in several states. I just checked Oregon and California and it is illegal in both. Your locality may be different. > **[California Motor Vehicle Code](https://www.bestattorney.com/california-motor-vehicle-code/)** > > Learn about the California road laws and contact the expert auto accident attorneys if you have suffered an injury on the roads. Free consultation, 99% success. > **[ORS 811.495 - Unlawful coasting on downgrade](https://oregon.public.law/statutes/ors_811.495)** > > ORS Title 59, Oregon Vehicle Code; Chapter 811, Rules of the Road for Drivers; Section 811.495, Unlawful coasting on downgrade; exception; penalty. Refreshed: 2023-06-16 ---
**Author:** ![chargerrich](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chargerrich/32/5399_2.png) [@chargerrich](https://boards.straightdope.com/u/chargerrich)\ **Post date:** [April 10, 2013, 4:38pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/31 "2013-04-10T16:38:14Z")
> [@GreasyJack](#): > > I suppose you can make some academic point about whether the engine is really “running” if it’s just being turned by the car’s inertia, but you’re completely wrong about this not being the norm for most cars. It has been for at least two decades. The driver doesn’t really notice since all the belt driven accessories are still turning and the engine can start producing power again instantly. Did a little Google-Fu and read up on Direct Fuel Cut Off… I stand corrected and thank you for information. Very interesting technology for as old as it is! Now I need to figure out how I am getting 42MPG on my little daily driver! ---
**Author:** ![chargerrich](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chargerrich/32/5399_2.png) [@chargerrich](https://boards.straightdope.com/u/chargerrich)\ **Post date:** [April 10, 2013, 4:41pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/32 "2013-04-10T16:41:43Z")
> [@RitterSport](#): > > It’s called deceleration fuel cutoff. You can search for DFCO to see it discussed elsewhere. > > If that’s not what’s happening, then explain this: > > Going downhill in my car, AC is on, put car in neutral – MPG gauge reads, say 130 MPG. > > Going downhill in my car, AC is on, leave car in gear and take foot off gas – MPG gauge immediately goes to “—”, basically, off the charts. I wonder if perhaps my scangauge cannot read this properly but when I am going downhill in gear on one stretch of my commute the gauge reads 60 or so MPG, but the second I put it in neutral it jumps to 199 MPG. That said, I read about the DFCO and it clearly says the ECU cuts fuel using wheel momentum to turn the crank so I am both educated and dumbfounded on the subject 😃 ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [April 10, 2013, 4:42pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/33 "2013-04-10T16:42:19Z")
What are the economics of this behavior? That is, if I am spending $250 a month in gas, this is going to save me, what, a couple of dollars? I mean, I don’t spend _that_ much time descending hills. A long-haul trucker, I could understand. Also, in some states it is illegal to coast. Don’t ask me how they could possibly tell. And I won’t debate the morality or wisdom of it. It’s just a fact. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [April 10, 2013, 4:48pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/34 "2013-04-10T16:48:28Z")
> [@ZenBeam](#): > > Does this all apply to automatics as well? Better mileage-wise to take my foot off the gas than to shift it into neutral? Yep. Automatics transmit power both ways too, so long as the fluid pump is already running. ---
**Author:** ![SmellMyWort](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SmellMyWort](https://boards.straightdope.com/u/SmellMyWort)\ **Post date:** [April 10, 2013, 4:54pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/35 "2013-04-10T16:54:10Z")
> [@Mangetout](#): > > Unless we’re talking about enormous long hills, or very steep ones, or low speed limits, that shift point is often nowhere near the bottom of the hill (and may in fact be right at the top). > > Because if you have engine-braked all the way down, your car isn’t suddenly going to make up speed on the last little bit of downhill slope. In my experience I’m not going to get any significant engine braking on a hill unless I’m in a lower gear. ---
**Author:** ![AdamF](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/adamf/32/6246_2.png) [@AdamF](https://boards.straightdope.com/u/AdamF)\ **Post date:** [April 10, 2013, 4:58pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/36 "2013-04-10T16:58:07Z")
> [@ZenBeam](#): > > Does this all apply to automatics as well? Better mileage-wise to take my foot off the gas than to shift it into neutral? You should never force a modern car with automatic transmission into neutral. The transmission itself can decide when the neutral is more advantageous and will disconnect the clutch. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [April 10, 2013, 5:00pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/37 "2013-04-10T17:00:42Z")
It depends on the slope, and whether you’d need to use brakes. It’s clearly a tradeoff between two factors. 1. In neutral, you have to burn gas to keep the engine idling 2. In gear, some engine breaking occurs, but no gas is needed to keep it turning. Also, the purpose of the brake pedal is to turn kinetic energy into heat, so clearly, using brakes rarely increases fuel economy. Modern engines do indeed cut fuel delivery, as has been cited in other related threads here on SD. I worked on engine control software at Ford SciLab decades ago, and was interested to learn what happens today. I found the cites in the other threads convincing, though I don’t remember the sources. In any case, I was a pro on this long ago, enough to be able to understand the jargon. I can’t do the math to find the tipping points between the two factors I listed above, but I’d guess that if you use the highest gear where your speed doesn’t exceed the safe maximum, that would be the most efficient. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [April 10, 2013, 5:03pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/38 "2013-04-10T17:03:48Z")
> [@chargerrich](#): > > Really not trying to be combative here, but I do not see how it would be possible to have any car that runs on fuel only (hybrids and electric excluded) and has an INTERNAL COMBUSTION engine that is RUNNING to not be burning some amount of fuel.- If the drivetrain is turning the engine and there’s no demand for power, it need burn no fuel. As soon as there’s demand for power, fuel delivery returns. I don’t know whether they also cut off spark when fuel delivery is off. My wild guess is no, because the added complexity wouldn’t be justified by the slight increase in spark plug life, and I can’t think of any other significant benefit. The energy use for spark is probable negligible. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [April 10, 2013, 5:07pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/39 "2013-04-10T17:07:40Z")
> [@Xema](#): > > The trick is to shift into neutral as you approach the bottom of the hill, such that you reach the maximum safe speed at the bottom and thus climb the next hill with the least expenditure of fuel. I don’t buy this. I don’t see any benefit to running in neutral in this case. The question would be whether the fuel to idle the engine is more or less than the amount of fuel to replace the kinetic energy lost to the (minimal) engine breaking in the highest gear. While you’re climbing the next hill but before you’ve pressed the gas pedal, you would want to be in the highest gear if engine breaking – assuming you’re going fast. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 10, 2013, 5:15pm UTC](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320/40 "2013-04-10T17:15:02Z")
> [@AdamF](#): > > You should never force a modern car with automatic transmission into neutral. The transmission itself can decide when the neutral is more advantageous and will disconnect the clutch. Automatics (except for some BMW Electrohydraulic transmissions, and perhaps other performance cars) don’t _have_ a clutch… [Previous page](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320.md?page=1) [Next page](https://boards.straightdope.com/t/for-better-mpg-shift-to-neutral-or-leave-in-gear/655320.md?page=3)