Engine Braking & Neutral Coasting: Gas Mileage Tested

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blahblah99

Platinum Member
Oct 10, 2000
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Originally posted by: VIAN
What I needed to answer was: Doesn't neutral coasting save gas? & Does engine breaking waste gas?
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No, neutral coasting requires the engine to idle at 800rpm or whatever it's normal idling speed because vehicle speed is irrelevant since the transmission is not in gear. So, coasting in neutral is essentially the same as idling in traffic as far as gas consumption is concerned.

Engine braking FORCES the engine to spin at a RPM determined by the speed of the vehicle and the gear that the transmission is in and hence, does not require FUEL AND IGNITION to keep the engine spinning. This is, of course, dependent on the design of the ECU of the vehicle.
 
dug777

dug777

Lifer
Oct 13, 2004
24,778
4
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Statement's like 'omg, use your brakes as brake pads are cheaper lol' miss the point. Driving shouldn't be 'omg i can save a few cents and get maybe a few more thousand ks out of my clutch', it should be using both your brakes and engine so ensure that you're in complete control of your car ;)

There's a very good reason coasting in neutral is a big no no, you've lost a lot of your ability to 'actively' avoid an accident until you've got the car back in gear. You should always be in a gear so that if you put your foot down, you can smoothly accelerate, or at least that's what i've always been taught...
 
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BD2003

Lifer
Oct 9, 1999
16,815
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Originally posted by: FrustratedUser
Originally posted by: ScottSwingleComputers
Originally posted by: FrustratedUser
Originally posted by: randay
Originally posted by: JulesMaximus
Jesus...haven't we discused this enough?
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As long as the engine is spinning it eats gasoline.
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*smacks forehead* No, no nooo.

*GROAN*
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Didn't we have 200 pages of this last week?
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At least 200....
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Baby jesus is crying.
 
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homestarmy

Diamond Member
Apr 16, 2004
3,528
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artwilbur.com
You have a good amount of data, too bad it is completely worthless.

Why did you bother if you couldn't accomplish AOTHC?

AOTHC - all other things held constant.
 
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homestarmy

Diamond Member
Apr 16, 2004
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artwilbur.com
Originally posted by: AgaBoogaBoo
I didn't read the whole thread, but in city driving just use the brake pedal to slow down, why put extra wear and tear on the clutch when it's not needed? Brake pads are cheaper and easier to replace than a clutch.
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If you are in gear, there is no wear on the clutch. Do you know how a car works? Coasting in neutral by disengaging the clutch, then engaging it again (this is where the wear occurs) will wear it down faster.

Engine braking saves wear on your brakes AND clutch in cases where you don't need to come to a complete stop or downshift.
 
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homestarmy

Diamond Member
Apr 16, 2004
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artwilbur.com
Originally posted by: snes tor
wouldn't the pistons stop moving then?
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No, the wheels are connected to the axles, which are connected to the transmission, which are connected to the clutch and flywheel, which are connected to the crank and rods, which are connected to the pistons.

At this point, they are compressing air, which is what causes the "drag" which slows you down in gear more vs coasting.
 
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homestarmy

Diamond Member
Apr 16, 2004
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artwilbur.com
Originally posted by: VIAN
I revised the OP, it may be easier to understand. Also the conclusion has changed. Previously, I was trying to see what saved more gas, normal driving, extreme engine breaking, or extreme neutral coasting + low rpm acceleration. But, then I realized that this wasn't what I was trying to answer.

What I needed to answer was: Doesn't neutral coasting save gas? & Does engine breaking waste gas?
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Which is why it was dumb that you were testing two variables at the same time: low accelleration vs high accelleration combined with engine braking vs not.

We already know high accelleration will change gas mileage, if this was a constant (though this would be an extremely dumb way to do it, only valid if this is the only possible way to test this data, which it is not) then you could monitor the difference in the expected value to find what change engine braking caused.

Plus, how did you measure MPG? With all of your other mistakes you MOST LIKELY have a flawed way of measuring that as well. Also, you would need to drive under the same conditions, who knows if you did?
 
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VIAN

Diamond Member
Aug 22, 2003
6,575
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Originally posted by: homestarmy
Plus, how did you measure MPG? With all of your other mistakes you MOST LIKELY have a flawed way of measuring that as well. Also, you would need to drive under the same conditions, who knows if you did?
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It can't be perfect. When the gas light comes on from my corolla, it means about 10 gallons are gone. Cause everytime I refuel when the gas light comes on, I get 10 gallons. Then I check the mileage. I've been driving through many different conditions every day before these test and I always used to get similar gas mileage. Like I said, it ain't pefect, but it's something.

 
R

randay

Lifer
May 30, 2006
11,018
216
106
Originally posted by: homestarmy
Originally posted by: snes tor
wouldn't the pistons stop moving then?
Click to expand...

No, the wheels are connected to the axles, which are connected to the transmission, which are connected to the clutch and flywheel, which are connected to the crank and rods, which are connected to the pistons.

At this point, they are compressing air, which is what causes the "drag" which slows you down in gear more vs coasting.
Click to expand...

the only way the pistons move is when the gas explodes and makes them move.
 
B

BD2003

Lifer
Oct 9, 1999
16,815
1
81
Originally posted by: randay
Originally posted by: homestarmy
Originally posted by: snes tor
wouldn't the pistons stop moving then?
Click to expand...

No, the wheels are connected to the axles, which are connected to the transmission, which are connected to the clutch and flywheel, which are connected to the crank and rods, which are connected to the pistons.

At this point, they are compressing air, which is what causes the "drag" which slows you down in gear more vs coasting.
Click to expand...

the only way the pistons move is when the gas explodes and makes them move.
Click to expand...

You're absolutely wrong. There is a physical connection between the pistons, through many different parts, to your wheels. Otherwise, your car wouldnt go anywhere when you stepped on the gas. As long as those wheels are spinning, and that system is fully connected through the transmission, the pistons MUST be moving as well.
 
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BD2003

Lifer
Oct 9, 1999
16,815
1
81
Originally posted by: supafly
Isn't it dangerous to coast in neutral?
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Theoretically yes, because you have to put it back in gear in case you have to accelerate out of the way of something.
 
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BD2003

Lifer
Oct 9, 1999
16,815
1
81
Originally posted by: randay
Ok this isn't even fun, people have such bad memory.
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But it isnt really funny to begin with. It was slightly funny 2 weeks ago. Now it's just old.
 
Vic

Vic

Elite Member
Jun 12, 2001
50,422
14,333
136
To the OP: the owners manual for your Toyota Corolla S specificially says not to operate the engine under load below 2000 rpm and that to do so can cause engine damage and shorten engine life.
Now how much money are you saving? ;)


And FYI to all: determining fuel mileage can be done through observing an intake manifold vacuum pressure gauge. The greater the vacuum, the less fuel is being consumed. This is exactly how "fuel computers" that are installed in certain car models work. They measure vacuum against vehicle speed. For those with turbocharged engines, a boost gauge can serve the same function (as it's just a vacuum gauge that can also measure positive pressure, aka "boost").
 
Vic

Vic

Elite Member
Jun 12, 2001
50,422
14,333
136
Originally posted by: BD2003
Originally posted by: supafly
Isn't it dangerous to coast in neutral?
Click to expand...

Theoretically yes, because you have to put it back in gear in case you have to accelerate out of the way of something.
Click to expand...

A car also handles worse in neutral than it does in gear. This is because steering inputs can be manipulated with the throttle as well as with the steering wheel. Skilled drivers know that you use the steering wheel to pick the line and then the throttle to make the fine tune adjustments to hold the line.
 
EarthwormJim

EarthwormJim

Diamond Member
Oct 15, 2003
3,239
0
76
Originally posted by: randay
Originally posted by: homestarmy
Originally posted by: snes tor
wouldn't the pistons stop moving then?
Click to expand...

No, the wheels are connected to the axles, which are connected to the transmission, which are connected to the clutch and flywheel, which are connected to the crank and rods, which are connected to the pistons.

At this point, they are compressing air, which is what causes the "drag" which slows you down in gear more vs coasting.
Click to expand...

the only way the pistons move is when the gas explodes and makes them move.
Click to expand...


Completely wrong, if that were so how do you explain people push starting their cars?

Or what about a starter? You think it doesn't move pistons?

In a fuel injected car i.e. basically any car that was made within the last 20 years, the fuel injectors DO shut off when coasting in gear.
 
N

natto fire

Diamond Member
Jan 4, 2000
7,117
10
76
It is ok to admit that you do not know how an engine works. I am not afraid to admit that I know diddly about PHP. However, on the same token, I don't chime in my opinion if there is a PHP thread knowing damn well I will be called out for trying to spread misinformation. Why is that so hard in this scenario?

For starters, the whole "anytime there is piston movement fuel is being consumed" is BS. An engine is basically an air pump, that especially as of late, can be controlled very precisely. Simple physhics would tell you that the kinetic energy developed from a reciprocating piston engine can come from a) chemical energy stored in gasoline b)inertia stored up from moving a 1-2 ton mass to a certain speed.

Yes, engines can absorb energy. Mad props to the people that are fighting this whole concept tooth and nail, but you are just wrong.
 
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