How To Increase Your Gas Mileage

monthtrial

Are you suggesting that leaving the car in gear while coasting yields greater fuel savings than placing the car in neutral?

When in motion, If idle RPM is @ 750, that should reduce fuel consumption as when the engine speed is @ 1K + RPM.

ZzzZz

He is saying that when coasting (foot off accelerator), it is better to leave it in gear rather than idle.

The reason being at idle you're burning gas at 750rpm with cylinders firing.

Staying in gear, even though you're at say, 3000rpm, not one drop of fuel is used (or close to that). The ECU cuts the gas completely off.

ChrisSlicks

Yep, what he said.

frost

^ interesting you say that, because when I'm looking at my instant fuel gauge, and I drop it into neutral, I will go into the 40mpg+ area, but it stays in the 20s if I just let off.
Thoughts?

ChrisSlicks

It goes 40+ in neutral but should go off the chart (60+) when you lift off completely.

frost

I'll have to give this a better look tomorrow, sure would be handy to stay in gear.

dad

Coasting in neutral consumes more fuel. In neutral, the injectors fire to keep the engine at idle, so you are burning fuel. Coasting in gear, the ECU switches to deceleration ... which happens to have an injector pulse width of zero.

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monthtrial

FYI: I'm no mechanic nor an auto engineer... just a dude using common sense and the fuel gauge read-out on my car...


I still don't understand why coasting in neutral would burn more fuel?

Are you suggesting that simply lifting OFF the gas consumes less fuel than placing the car in neutral to idle @ 750 RPM? I think there's a direct correlation between fuel consumption and RPM range - unless you're bogging the engine or loading it.

If your theory is correct, I could be driving down hill in second gear @ 6,000 RPM with my foot off the gas pedal (yet maintaining speed due to gravity & slope/grade) and save more fuel than popping it in neutral.

Very, very arguable, irrespective of however technical you may wanna get w/ injectors or widths.

Sure, there may be a point at which the speed one drives w/ the foot off the fuel pedal conserves fuel, but gearing and velocity have to be factored in and there comes a point where idling and maintaining a certain momentum (vs. losing momentum due to engine speed slowing the car) is more efficient.


Can you refute my non-technical assessment? If so, please do so in plain english.

armensti

let me just clear one thing out. i didnt get the z to drive like a granny, thats before breaking it in. as soon as i do im going to be flying

k.alexander

I've read here a few times that coasting in gear, gets you better mpg than dropping to neutral. Although this was a rather weird idea at first, I actually believe it. I have paid attn to that constantly moving horizontal bar graph in the Z's computer readout. It is true, when lifting off the gas and coasting in a gear, at higher speeds, the bar graph reads completely full (i.e. 60mpg or however high it goes up to); this is not true for when you drop into neutral, it shows like 40s or something.

That alone convinces me that you're better off coasting in gear.

Finally, I drive highway a lot, long trips for work. I've done this a few times, setting the cruise to 75mph. On one 200 mile trip, I averaged 27.7 mpg; on a second, slightly shorter trip, I averaged 28.5 mpg.

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monthtrial

Someone should try this and report to us the finding:

1. Find a stretch of road (at least a mile) w/ a slight grade.
2. Warm-up car and go to the top of this "hill".
3. Reset fuel mileage gauge and immediately perform step 4.
4. Accelearte from first gear to 25 MPH at a steady rate.
5. Place car in 3rd gear and coast to bottom of "hill".
6. Record mileage info.
7. Perform steps 1 through 4.
8. Place car in 4th gear and coast to bottom of "hill".
9. Record mileage info.
10. Perform steps 1 through 4.
11. Place car in 5th gear and coast to bottom of "hill".
12. Record mileage info.
13. Perform steps 1 through 4.
14. Place car in 6th gear and coast to bottom of "hill".
15. Record mileage info.
16. Perform steps 1 through 4.
17. PLACE CAR IN NEUTRAL AND COAST TO BOTTOM OF HILL.
18. Record mileage info.


While this is not entirely scientific, it should produce consistent results. Ideally, we want to maintain consistent tire, engine oil and road temps. Same goes for the weight in the car (passengers, luggage, etc)... and if you test w/ the windows up or down, do so in every instance of this test.

If I were a betting man, I'd say Neutral will generally yield better mileage, especially as slope (and speed potential) increases!