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Author Topic: Does coasting in neutral use more fuel?  (Read 38624 times)

Offline peppercorn

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Re: Does coasting in neutral use more fuel?
« Reply #25 on: 07/01/2012 15:16:45 »
Good point PC. So that would mean you might do slightly better if you do stay in gear. Mind you, if you are going to stay in gear, you have to keep changing down if you don't want to stall the engine.
Correct - it should be possible to return a very slight improvement in MPG if staying in gear, but as you infer there is a fairly limited rev range that this will mode support. The need to change gear at any point during deceleration would likely negate the gains anyway as the ECU would drop out of the 'fuel-off' mode in the change.  However a semi-auto gearbox might be able to handle the changes whilst staying in an efficient envelope.

I have a suspicion that most people, if they think are going to come to a complete stop, either disengage the clutch, or stick it in neutral (except during their driving test, of course.)
This is probably exactly the sort of behaviour the DVLA, in their rather clumsy way, are attempting to change through the pamphlet that Chris was sent :)


Clifford, I've always suspected that IC vehicles converted to battery-electric end up with somewhat more gears than are actually required, due to the wider torque range generally available from an EM.  Of course, since your truck falls into the good-for-towing category of vehicle that you Yanks are so keen on I guess the more gears the better :D
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #26 on: 07/01/2012 19:08:17 »

Of course, since your truck falls into the good-for-towing category of vehicle that you Yanks are so keen on I guess the more gears the better :D


It's Ford Ranger! (I think they have them in the UK too). I had a four-banger Ranger, and it couldn't pull the skin off a rice pudding. It could barely tow my little tin boat.
 

Offline CliffordK

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Re: Does coasting in neutral use more fuel?
« Reply #27 on: 07/01/2012 19:32:54 »
It's Ford Ranger! (I think they have them in the UK too). I had a four-banger Ranger, and it couldn't pull the skin off a rice pudding. It could barely tow my little tin boat.

Aw, Heck, my old 4-Banger Ford Ranger was a towing/hauling machine. [8D]
If it only had overload springs. :P

I could get one car loaded in the bed, and pulling another on a trailer   :D

The EV Ranger has a very nice tow hitch.  However, it is very very gutless  [xx(]
I'm also having range problems.  I was getting 35-40 miles this summer.  But, this winter, the range seems to be plummeting to under 20 miles  :(
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #28 on: 07/01/2012 20:54:48 »

I'm also having range problems.  I was getting 35-40 miles this summer.  But, this winter, the range seems to be plummeting to under 20 miles  :(


Are you running the heater, or do you think the battery capacity is reduced by the cold temps? Is it lead-acid?
 

Offline CliffordK

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Re: Does coasting in neutral use more fuel?
« Reply #29 on: 07/01/2012 21:08:10 »
Lead Acid...  or AGM.

It should have an option to heat off of the motor, but it doesn't. 
Sometimes I'll hit the electric heater for a few minutes to help defog the windows, but generally don't drive with it on.

I think it is reduced battery capacity from the cold weather.  We'll see what it is like next spring.  I do need to try to equalize the batteries sometime.
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #30 on: 08/01/2012 07:51:42 »
Can you monitor the voltage on each battery during charge and discharge?

I'm wondering if you might have a couple of dud cells, although, it that were the case, I would think you would see the charge current drop-off too quickly.
 

Offline neilep

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Re: Does coasting in neutral use more fuel?
« Reply #31 on: 08/01/2012 19:42:19 »
If ewe turn the engine off then this helps to save fuel too whilst coasting !..........which is nice !
 

Offline CliffordK

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Re: Does coasting in neutral use more fuel?
« Reply #32 on: 08/01/2012 20:03:32 »
If ewe turn the engine off then this helps to save fuel too whilst coasting !..........which is nice !
I've done it a few times.
Make sure you don't lock your steering, or are at least careful to unlock it.
Power steering will loose its assist, but may not be a problem at high speeds.
One gets one chance to pump the brakes before one also looses the power brake boost (but can still brake with more force).
If you have a manual transmission (with synchros), it s easy enough to pop the clutch to restart the engine. 
If, on the other hand, you have an Automatic Transmission in the USA, you may need to stop your vehicle and put it in park to restart, which is a big pain, and wouldn't be worth it, except for the biggest of hills.

A Hybrid does it all for you  ;)
 

Online chris

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Re: Does coasting in neutral use more fuel?
« Reply #33 on: 08/01/2012 22:12:48 »
200 amps; that's a serious current - surely that's not maintained during steady speed...?
 

Offline CliffordK

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Re: Does coasting in neutral use more fuel?
« Reply #34 on: 08/01/2012 22:37:21 »
200 amps; that's a serious current - surely that's not maintained during steady speed...?
It is serious current.

200A x 144V.

I generally pull just over 200A while going uphill, and on hard acceleration. 
I avoid the freeway whenever possible, but I've been on the freeway for short hops at times.  Fast driving, but high power consumption.
I prefer to cruise somewhere around 80A. 

In about an hour of driving, I can essentially go from full to empty on 24 batteries.

If you consider power this way.
for conversions, 1KW (VA) = 1.34 HP.

So..
200A x 144V = 28.8 KW.

So...  My Ranger has a max of about 40 HP.  That puts it about the same as the old VW Bugs.
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #35 on: 08/01/2012 23:57:09 »
200 amps; that's a serious current - surely that's not maintained during steady speed...?

It's relatively small compared to the energy consumed when you burn gasoline.

Clifford's electric Ranger is consuming around 6.5kW while cruising (80x144=6544) which sounds about right. If his Ranger was gasoline powered the engine would produce about 6.5kW under the same conditions.

However, as the engine would likely be around 25% efficient, it would be burning gasoline to produce 26kW.

The equivalent current for a voltage of 144V at that power level would be 181 amps, and if the engine was working hard, the equivalent current could easily be ten times greater.
 

Offline peppercorn

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Re: Does coasting in neutral use more fuel?
« Reply #36 on: 09/01/2012 14:25:33 »
I'm also having range problems.  I was getting 35-40 miles this summer.  But, this winter, the range seems to be plummeting to under 20 miles  :(

I think all battery techs. suffer from reduced efficiency in the cold (something to do with increased internal resistance perhaps?).
What you need is some nice low-value fuel (in terms of capacity to do useful work at cost) that is onboard simply to warm the batteries and the cabin.  The simplest vs cheapest heater would probably be Propane, but it's hardly in keeping with the electric 'values'.
I reckon Torrefied Wood (think efficiently produced charcoal) is a pretty interesting and underutilised source of cheap heat (and even mech work) especially if you want to move said source around (ie. vehicles).
 

Offline CliffordK

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Re: Does coasting in neutral use more fuel?
« Reply #37 on: 10/01/2012 06:01:12 »
What you need is some nice low-value fuel (in terms of capacity to do useful work at cost) that is onboard simply to warm the batteries and the cabin.
It turns out that I have one of these laying around the house.

I hate to think what the covering might be made of.
 

Offline peppercorn

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Re: Does coasting in neutral use more fuel?
« Reply #38 on: 10/01/2012 13:17:57 »
I hate to think what the covering might be made of.
Oooo! Dreaded asbestos!
 

Offline wolfekeeper

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Re: Does coasting in neutral use more fuel?
« Reply #39 on: 21/01/2012 06:17:38 »
Good point PC. So that would mean you might do slightly better if you do stay in gear. Mind you, if you are going to stay in gear, you have to keep changing down if you don't want to stall the engine.
Correct - it should be possible to return a very slight improvement in MPG if staying in gear, but as you infer there is a fairly limited rev range that this will mode support.
I'm possibly the only person in this thread that has actually done this with a real-time MPG meter.

On an old BMW I had the engine had this kind of fuel cut-off. The cut-off works over almost the whole rev range; the only conditions for activation was being above a thousand RPM or so and with your foot off the throttle; and I don't think it did it on a cold engine, because the automatic choke was trying to keep the engine running and warming up.

So all you do to activate it is change down and use engine braking. The fuel MPG just wacks off up to infinite when you do that, and you get better engine braking than you would if it hadn't... until you get low enough revs and then it feeds the fuel back in again to stop the engine stalling, and you get a slight lurch- it's not possible to stall it this way on an automatic.

I'm pretty much certain that the same system is present on very many manual gearbox cars, it's cheap to install for the manufacturer and it improves engine braking performance as well as mileage, you just have to change down and use engine braking to use it.

As others have noted you get slightly better mileage than if you just used the brakes to stop; if you did that, because it was an automatic gearbox, the engine would drop to idle and the fuel wouldn't get cut; you had to deliberately select low gear to pull the revs up to use it.
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #40 on: 21/01/2012 06:31:06 »

I'm possibly the only person in this thread that has actually done this with a real-time MPG meter.


Oh yeah? I made my own digital MPG meter and stuck it in my VW in 1974.
 

Offline wolfekeeper

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Re: Does coasting in neutral use more fuel?
« Reply #41 on: 21/01/2012 07:01:50 »
Sure, I'm not saying that, sounds fun, but a 1974 VW probably didn't have a fuel injection system, this cut-off trick is done by the fuel injection system.

I used to routinely do this trick on my beemer, I also did mild hypermiling techniques including this one with it during the tanker strike; a 2.7 liter automatic is not the best type for that though, but it did seem to work!
« Last Edit: 21/01/2012 07:04:05 by wolfekeeper »
 

Offline CliffordK

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Re: Does coasting in neutral use more fuel?
« Reply #42 on: 21/01/2012 08:59:41 »
I know that my old 84 Renault Encore had an electronic idle speed adjustment screw...
Until something fouled up with the system, and I replaced it with a bolt.

Anyway, I think the car had some kind of electronic in carburetor injection.
 

Offline peppercorn

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Re: Does coasting in neutral use more fuel?
« Reply #43 on: 21/01/2012 14:27:24 »
I'm possibly the only person in this thread that has actually done this with a real-time MPG meter.

Good to hear it! Shame ya beemer was an automatic though - at least in economy terms.  Some ecomodders go as far as fitting an injector kill-switch - so taking manual control of their fuel feed. It can apparently be of use if using the Pulse & Glide style of motorway driving (if you're courageous enough to do it!).
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #44 on: 21/01/2012 18:58:44 »
Sure, I'm not saying that, sounds fun, but a 1974 VW probably didn't have a fuel injection system, this cut-off trick is done by the fuel injection system.


Yes, it had a carb, but it actually did have a fuel shut-off solenoid (althought that was there to make sure the engine would stop when you turned off the ignition!)
 

Offline wolfekeeper

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Re: Does coasting in neutral use more fuel?
« Reply #45 on: 22/01/2012 06:23:38 »
I'm also having range problems.  I was getting 35-40 miles this summer.  But, this winter, the range seems to be plummeting to under 20 miles  :(
I think all battery techs. suffer from reduced efficiency in the cold (something to do with increased internal resistance perhaps?).
What you need is some nice low-value fuel (in terms of capacity to do useful work at cost) that is onboard simply to warm the batteries and the cabin.  The simplest vs cheapest heater would probably be Propane, but it's hardly in keeping with the electric 'values'.
I reckon Torrefied Wood (think efficiently produced charcoal) is a pretty interesting and underutilised source of cheap heat (and even mech work) especially if you want to move said source around (ie. vehicles).
You can also use electric heaters when plugged in, and the battery may be able to power the heater itself when it's not (with some reduction in range). That's how the Tesla works, it has the same potential problem.
 

Offline peppercorn

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Re: Does coasting in neutral use more fuel?
« Reply #46 on: 22/01/2012 15:01:49 »
You can also use electric heaters when plugged in, and the battery may be able to power the heater itself when it's not (with some reduction in range). That's how the Tesla works, it has the same potential problem.

Yes, Tesla have gone for the simplest solution to cabin heating; with the Tesla being marketed as a sports car (esp. as it's a two-seater, usually with a soft top) I doubt the average driver is necessarily too worried about a heater anyway!
The thing to remember is electricity is pretty much the highest value energy source there is - so wasting it on making low-value heat seems rather a crime really!
OTOH, I can see that a (mains) plug-in heater option both to pre-heat the battery-box (improving range) and cabin pre-heat (or even a small onboard P.C.M. module) could represent the best compromise between fuel value and simplicity.
Personally I'd still want a small butane heater or similar for those longer journeys though; at least for a car with a 'proper' tin roof ;D.
 

Offline Geezer

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Re: Does coasting in neutral use more fuel?
« Reply #47 on: 22/01/2012 18:34:28 »
Personally I'd still want a small butane heater or similar for those longer journeys though; at least for a car with a 'proper' tin roof ;D .

Ewe could always take a hot-water bottle with ewe.
 

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Re: Does coasting in neutral use more fuel?
« Reply #47 on: 22/01/2012 18:34:28 »

 

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