questionable driving technique

dhjjessel

dhjjessel

dhjjessel

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Joined
18 Oct 2002
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675
Location
England's Green and Pleasant Land
Because i do a lot of urban driving, i find that i am braking about as much as i am accelerating. I have picked up the habit of accalerating up to a certain speed, then putting my gearstick in neutral and gliding along behind other traffic, not using the engine...
i know that you lose a certain amount of control by not being in gear, but i tend to be going between 20 and 30 mph when i am doing it. Is this a bad method for another reason?
 
True you lose your engine breaking ability.

Instead of accelerating and then braking, howabout chugging along in say 2nd/3rd at idle revs. Leave plenty of gap between you and the car infront and you will have to do much less braking.
 
When in neutral you have no control over the cars speed, it also uses more petrol than if you were in gear with no throttle applied.
Try looking further ahead so you can match speed and not having to slow down all the time.
 
Perhaps surprisingly, it's also less fuel efficient to leave a car in neutral.
When a car is coasting in gear, momentum from the car is able to keep the engine running. I'm told that most new engines now deliberately underfuel to take advantage of this, thus using less fuel that even at tickover.
 
Acolyte said:
The injectors are shut off all togother on modern injection systems
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Whilst slowing down in gear yes, some fuel will be used when moving along on idle revs, whether this is equal to the same fuel consumption as in neutral I am not sure. You get motion out of it instead of nothing so it cant be a bad thing
 
so when i go along with my car in neutral, even though its going at about 800rpm, its using more fuel than if i was going at the same speed in 2nd gear at 2000 rpm?
 
dhjjessel said:
so when i go along with my car in neutral, even though its going at about 800rpm, its using more fuel than if i was going at the same speed in 2nd gear at 2000 rpm?
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If your throttle is closed, yes, as your using momentum to move you, not the engine. When the revs are idle, the engine needs to use petrol, as otherwise the engine will stall.
 
dhjjessel said:
so when i go along with my car in neutral, even though its going at about 800rpm, its using more fuel than if i was going at the same speed in 2nd gear at 2000 rpm?
Click to expand...

It depend on how much throttle you need to keep it at 2000 rpm.
What you could do is stick it in 3rd and see how fast that moves you at idle.
In neutral at 800 rpm you are definitely *wasting* fuel as you are burning it just for power steering/electics etc. In gear you at least get some motion out of it.

If you want to improve fuel efficiency then see how fast you will go at idle revs in 1st/2nd/3rd/4th and and use those gears to creep along in traffic at the appropriate speed. However if you are at ~20 mph in 4th at idle then I wouldnt acclerate in that gear, change down.
 
chrislusty said:
If your throttle is closed, yes, as your using momentum to move you, not the engine. When the revs are idle, the engine needs to use petrol, as otherwise the engine will stall.
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Erm, no :confused: You don't use momentum, the engine is working and driving the car forward, which is why it stalls if you break without dipping the clutch. The engine always generates a torque resulting in forward motion when in gear, which is only stopped through clutch dipping/going into neutral.
 
Ex-RoNiN said:
Erm, no :confused: You don't use momentum, the engine is working and driving the car forward, which is why it stalls if you break without dipping the clutch. The engine always generates a torque resulting in forward motion when in gear, which is only stopped through clutch dipping/going into neutral.
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Release the throttle in 2nd at 2000 rpm and you should use next to no fuel while you slow down to idle revs.

The forward momentum of the car is sufficient to turn the engine over. Once the rev drop to near idle I suspect the ECU starts fueling again to keep you running and stop you stalling.

The situation you describe will of course be fueling as you are below idle revs.

I suspect people are saying the same things in different ways and not interpretings others correctly
 
Ex-RoNiN said:
Erm, no :confused: You don't use momentum, the engine is working and driving the car forward, which is why it stalls if you break without dipping the clutch. The engine always generates a torque resulting in forward motion when in gear, which is only stopped through clutch dipping/going into neutral.
Click to expand...

That was true with carb fed engines, but doesn't apply to modern ECU controlled engines which can shut fuel off entirely if it's unnecessary.

As for abusing the clutch and gearbox less, I have to say 'huh'? gearboxes and clutches are affected by moving gears in and out of mesh, and that's what you do every time you put it into neutral then back into gear later... It's better for both to leave it in gear.
 
It really depends if you're using the engine to move you along, or deceleration / a downward gradient.

If you're in 2nd on level ground and you're maintaining speed, the engine is using fuel to propel you forward regardless of if the throttle is pressed or not as the idle control valve will keep the engine running.

Its only when you're using engine braking that the injectors shut off.
 
What a stupid thread :p

In a fuel injected car if you're not accelerating then the ECU will only be putting in enough fuel to maintain your speed.

If you're coasting chances are you're decelerating so you'll have to give it some gas to bring your speed up again. Technically this requires the charge to be enriched slightly so you'll use more petrol, plus the matching of the revs, plus the extra clutch action.

Come to think of it same goes for a carbed car.
 
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