Stop/start? What we need is drive/neutral....for massive MPG savings

MarkDavis

MarkDavis

MarkDavis

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The fuel saving is massive - typically 30-40% - when covering a route and coasting where feasible, compared to the same route when the engine is in gear and providing engine braking. When you're in a gear, the ludicrous the number of times during a journey you for example, see traffic lights 800 yards ahead, accelerate up to them, the brake to slow down.

Yes, its potentially an offence to be coasting but these days with DSG and gears engaging in a few milliseconds, I cannot see why there should be any safety disadvantage. As soon as you touch the throttle for example, the car snaps into gear with a DSG type box.

Government needs to add a 'carve out' in the legislation of the wording to allow for coasting if its built into the car through the gearbox and manufacturers should think about implementing it.
 
MarkDavis said:
The fuel saving is massive - typically 30-40% - when covering a route and coasting where feasible, compared to the same route when the engine is in gear and providing engine braking.
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Cite your source. Everything I've read says to leave the car in gear with anything halfway modern.
 
I suppose one could get used to it, but ISTR that one of the unexpected (But actually quite serious) problems with the Rover Gas Turbine prototypes was that there was no engine braking.

Drivers are used to cars slowing down when you take your foot off the gas and the test drivers on the rover found that the absence of it was most disconcerting.

(It also meant that the car ate brake pads! Though I imagine that a system using electric braking for light braking could overcome this)

As an aside I also STR that some of the early Saabs had a centrifugal clutch which would disengage on overrun. How the legislation (Or indeed the drivers!) of the day dealt with that, I do not know.
 
I'm guessing you're determing the fuel savings by looking at the trip computer as mine used to show 999mpg while coasting. As far as I know the injectors are still active while coasting so fuel is still being used.

When you're in-gear with feet off all pedals and above certain rpm's the injectors will switch off and you'll be using no fuel. Of course you'll also slow down quicker than coasting due to engine braking.

I got to say, I don't agree with the whole coasting is dangerous thing. It's not that hard to keep an eye on your speed and braking/steering seems unaffected.
 
Hmm, I thought the exact opposite of OP. I thought that in gear coasting (overrun) the fuel injectors are shut off, and it's using no fuel... whereas in neutral it's running at idle speed so the injectors are still squirting.
 
Westyfield2 said:
Hmm, I thought the exact opposite of OP. I thought that in gear coasting (overrun) the fuel injectors are shut off, and it's using no fuel... whereas in neutral it's running at idle speed so the injectors are still squirting.
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Yes you are correct. It's just another bizarre MarkDavis thread
 
JRS said:
Cite your source.
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Me. Obviously, I've road tested this with a route that I regularly drive. The fuel savings are massive, particularly on sections of clear, straight roads punctuated by traffic lights where you're constantly having to accelerate and them stop.

Zbornak said:
I thought any vehicle with fuel injection is more economical in-gear, rather than neutral?
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In neutral (ie the engine idling), the fuel economy is 100mpg+. In gear with drive train losses and having to pull a 1.5 ton vehicle and it drops to your typical 20-30mpg when you're accelerating.

Howard said:
Yes you are correct. It's just another bizarre MarkDavis thread
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You don't half embarrass yourself with your ignorance every time you post...
 
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MarkDavis said:
In neutral (ie the engine idling), the fuel economy is 100mpg+. In gear with drive train losses and having to pull a 1.5 ton vehicle and it drops to your typical 20-30mpg when you're accelerating.
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Yes but when you let off the accelerator to slow down, you're using less fuel than if you drop it into neutral and coast to a stop. Which will take ages on its own, so you'd have to use the brakes more, which would wear the brake pads out faster, and the cost of more frequent replacement brake parts would negate these fictitious fuel savings.
 
Lol MarkDavis.

MarkDavis said:
Me. Obviously, I've road tested this with a route that I regularly drive. The fuel savings are massive, particularly on sections of clear, straight roads punctuated by traffic lights where you're constantly having to accelerate and them stop.



In neutral (ie the engine idling), the fuel economy is 100mpg+. In gear with drive train losses and having to pull a 1.5 ton vehicle and it drops to your typical 20-30mpg when you're accelerating.
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Shock as accelerating uses more fuel than not accelerating.

Sounds more like you're failing to read the road ahead and so forcing yourself to drive more appropriately by taking it out of gear so your usual accelerate-brake routine is pointless, is improving your economy.

In gear when you're decelerating, your mpg will be infinite. Out of gear, you will be using 10-20ml/minute depending on car etc. Normally when you coast you will be going sufficiently fast (generally more than 15-20mph) that this will be displayed on the trip computer as e.g. 100+ and thus it fails to differentiate between infinite and high, the car slows down quicker on infinite, and the assumption is that coasting is therefore more efficient.
It isn't, drive in gear and to the road without pointless acceleration/braking and not only will you save fuel but you'll also save on tyres, brakes and stress levels.
 
MarkDavis said:
In neutral (ie the engine idling), the fuel economy is 100mpg+
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But in-gear with zero throttle input (ie, in 5th) the economy is infinitempg because modern fuel injection engines cut the fuel supply.

Obviously coasting will be more efficient than lifting off in 2nd as the engine braking in 2nd will slow you quite quickly, but if you leave it in 5th instead of neutral you'll benefit from more roll before you need throttle *and* nil fuel usage.
 
Neutral will cause the engine to rev slightly higher than idle to prevent stalling.

Coasting in gear in modern fuel injection cars will cut off the supply thus using zero fuel.
 
[TW]Fox;25828864 said:
But in-gear with zero throttle input (ie, in 5th) the economy is infinitempg because modern fuel injection engines cut the fuel supply.

Obviously coasting will be more efficient than lifting off in 2nd as the engine braking in 2nd will slow you quite quickly, but if you leave it in 5th instead of neutral you'll benefit from more roll before you need throttle *and* nil fuel usage.
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No idea what you said there, but no, you do not have 'nil' fuel usage. You also seemed to have overlooked the fact that being in 5th significantly slows the car more than being in neutral.
 
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Modern makes me chuckle a little. Modern and 20 years ago. Anything with a cat will have overrun fuel cut otherwise the kitty dies, it is nothing new.
 
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