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

[Barks]

This thread is just the ultimate face palm.

As discussed in gear as soon as you take your foot off the accelerator the fuel injection into the engine is cut off. In neutral there is always fuel being injected into the engine to keep it ticking over which is why you cannot stall a car in neutral or with your foot dipped on the clutch. Therefore on a downhill gradient you are using less fuel by sticking it in the highest possible gear as opposed to putting it in neutral.

 

[Pants]

There's ignorance getting in the way of the actual question.

1: Use engine breaking (no fuel, but speed loss) and have to accelerate sooner (more fuel)
2: Coast in neutral (a little fuel, less speed loss) and being able to accelerate later (small fuel saving)

Using the coasting method, does the MPG increase of getting to accelerate later mitigate the fuel used idling the engine?

 

[Pants]

This thread is just the ultimate face palm.

As discussed in gear as soon as you take your foot off the accelerator the fuel injection into the engine is cut off. In neutral there is always fuel being injected into the engine to keep it ticking over which is why you cannot stall a car in neutral or with your foot dipped on the clutch. Therefore on a downhill gradient you are using less fuel by sticking it in the highest possible gear as opposed to putting it in neutral.

That's assuming the gradient is steep enough to maintain speed in gear. What if it's not?

 

[Janesy B]

That's assuming the gradient is steep enough to maintain speed in gear. What if it's not?

Only needs to be a very slight gradient tbh.

 

[SDK^]

Drive in neutral for massive MPG savings - why didn't someone think of doing this sooner

Another classic OcUK motors thread.

 

[Clarkey]

Of course there's engine breaking in 5th. There are also drivetrain energy losseands.

And as for no fuel usage, what do you think is powering the engine when you have your foot off the accelerator? Ribena?

You really did fail your 11+ didn't you?

Lol too funny. Look up how a cars transmission engine and wheels are connected, then think about momentum and potential energy.
Preaching about this yet not understanding the basic physics behind it, priceless.

 

[Pants]

Only needs to be a very slight gradient tbh.

My engine braking is fairly severe. But if it is steep enough you can't argue against engine braking.

There's only really a valid debate if it's a more gradual slope.

edit: I'm off for now, look forward to my car stalling tomorrow when I lift off the throttle in 5th.

 

[Barks]

That's assuming the gradient is steep enough to maintain speed in gear. What if it's not?

Whether you're in gear (using no petrol) or coasting in neutral (using petrol to keep the engine ticking over) on a slope of level or increasing gradient the momentum will eventually run out and you will need to engage a gear and use the accelerator.

There's ignorance getting in the way of the actual question.

1: Use engine breaking (no fuel, but speed loss) and have to accelerate sooner (more fuel)
2: Coast in neutral (a little fuel, less speed loss) and being able to accelerate later (small fuel saving)

Using the coasting method, does the MPG increase of getting to accelerate later mitigate the fuel used idling the engine?

You do realise even on the slightest downhill gradient gravitational potential energy will keep the car accelerating regardless of the engine breaking effect of remaining in gear. Therefore your point is invalid.

 

[planty]

There's ignorance getting in the way of the actual question.

1: Use engine breaking (no fuel, but speed loss) and have to accelerate sooner (more fuel)
2: Coast in neutral (a little fuel, less speed loss) and being able to accelerate later (small fuel saving)

Using the coasting method, does the MPG increase of getting to accelerate later mitigate the fuel used idling the engine?

Agree with this. Regardless of the actual mpg difference between the 2 methods, I'm certain one isn't 30-40% better than the other in a fair test, as MarkDavis is suggesting.

 

[Fr0dders]

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.

entirely situational.

I drive down this 1.5 mile hill every day on the way to work. Its got a nice gentle incline and a 60 limit

https://maps.google.co.uk/maps?q=LS...id=FQLSQz7qyJCUEJvyDm1ARg&cbp=12,35.32,,0,6.7

assuming you don't get a 30mph moron you can usually coast down the thing with your foot off the gas in 5th and just let the wheels turn the engine. Infinity MPG all the way.

 

[Jonnycoupe]

Manufacturers don't do it as it doesn't fit NEDC anyway, stop start does and justifies the extra component costs.

 

[haaammit]

Why does my fuel injected engine's exhaust pop and flame on the over-run if there's no fuel going through the engine? Genuine question

 

[Mr_White]

... Why do some of you not understand cars in the slightest?

 

[Begbie]

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.

This is true, thread is bizzare.

 

[Conscript]

Isn't that unburnt fuel getting ejected from the cylinder and igniting in the exhaust?

Edit: aimed at Barry

 

[Scania]

Thread is IMO silly, wrong and potentially dangerous.

 

[Jonnycoupe]

Why does my fuel injected engine's exhaust pop and flame on the over-run if there's no fuel going through the engine? Genuine question

They inject the fuel to do that.

 

[Havana_UK]

I read the Terraclean thread and thought "hmm, maybe", since I've no knowledge or experience of my own to draw upon, then I read this...


...and laughed my arse off!

Mark, you are wrong I'm afraid (unless you're driving a car from 1980-something). Today's engines use NO FUEL AT ALL when coasting in gear, an idling engine uses fuel, ergo a car coasting in gear is more fuel efficient than a car coasting in neutral.

 

[shaank]

thread has caught my interest for some of the attempts at understanding engines and coasting

/awaits the first person to claim they now drive everywhere in neutral and use no fuel at all

 

[86JR]

Audi do this already

When the driver chooses the efficiency mode in the Audi drive select, the S tronic opens the clutch when the vehicle is in overrun – and the sporty SUV coasts along, reducing its fuel consumption even further.