samjcg

iTrader: (17)

believe it or not... I made a thread saying "Down side of my ZZZZZZ" I started saying about my bad mpg but somehow the conversation zoned out and went to Coasting in Nuetral waste Gas or NOT!!!
I guess we can debate about this on this NEW TREAD!!!! so please reply with YES/NO Answer... thanks

sam

Anomaly

iTrader: (7)

ok...


Coasting in neutral *should* conserve fuel but since there's relatively few times where one will coast for miles (in SoCal: coming down the El Cajon Pass on the I15 is a prime example), the result will proabably not appear significantly as compared to the length of time spent on the gas.

Phenom

iTrader: (4)

I heard it uses less gas than downshifting because you aren't blipping the throttle. I mean you could just downshift with no blip, but then your shifting causes your passenger to go "OMFGWTF teh n00b shift." Also there's no engine braking while in neutral.

I really have no clue though, maybe neutral does use more for some reason? Anyone wanna chime in?

stylett9

iTrader: (9)

It is better to leave in gear.

It could be more beneficial then you think.

I often find myself shifting into neutral early when coming up to stops, lights, or going down hills...anything of the such.

You don't necessarily have to downshift, but lets say your coasting in 3rd or
4th and you see a light turn red or you see a stop sign coming up. Just leave it in gear until your almost at a stop, then shift to neutral. You dont necessarily have to keep the RPM range in 3-4 or anything of the such. If you are in 3rd gear and your are 4k RPM, just ride it all the way down to 1200-1500 before going to neutral. Being done constantly through the life of your gas tank, it could add up to help save quite a bit?

In the other thread i was taking the opposite stance and am pretty convinced i'm wrong now. lol

Azrael Z06

Ahh... No it will waste fuel compared to coasting in gear, but conserve fuel compared to driving WOT in a lower gear.

While coasting in gear, say down a grade, engine braking will save fuel because the PCM cuts fuel to the fuel injectors to slow the engine down. The engine is kept running by drivetrain inertia, making it a de facto air pump. As soon as the clutch goes in to coast the PCM will then feed fuel to the engine to keep it at idle speed relative to the idle air supplied (throttle).

Coasting in nuetral will save gas only compared to acceleration, and not coasting in gear (engine compression braking).

Key Of Z

As long as you're not pressing on the accelerator, you're not using any more gas than you would use to coast. Never a good idea, btw.

Azrael Z06

Actually if you are coasting (no throttle) while in gear, you are using no gas at all. Like slowing down for a stop or using the engine to slow (or keep a steady speed) in gear down a hill or long grade.

infiniteracing

iTrader: (2)

If your coasting at 3000 rpms you are using more gas than if you put it in neutral and it sits at 1200 rpms

If you're using no gas at all, then how does your engine maintain rpms? Actually any time your engine is on, it's using gas.

All electronically controlled fuel injected engines work like this. pressing down on the gas does not directly reflect how much gas goes in the cylinders. It's mandated by the computer and how many rpms your at. Fuel hasn't been directly linked to the "gas pedal" since carburetors, which is why old muscle cars have a tendency to cut out if you go wide open throttle and then lift all the way off the gas.

Key Of Z

That is correct, sir.

UMW350Z

iTrader: (18)

if you cost in nuetral and need the power right away for someone pulling out right in front of you or avoiding someone/something/an animal...you won't have it of course. I always leave it in until I am ready to blow my.....oops! stop the car...yea yea...stop the car.

Spike100

Easy... When the car is in motion, it should be in gear. When the car is sitting still, it should be in neutral.

--Spike

SniperHunter

iTrader: (9)

I've always thought it wasn't so great for the transmission to coast in neutral. Am I wrong?

redlude97

iTrader: (11)

Incorrect, almost all new EFI systems cut all fuel when coasting in gear, coasting in gear at 3k is due to engine speed driven by the gear ratios that mandate that rpm. The inertia of the car spinning the wheels transfers through the drivetrain back to the engine to spin it without the need for any combustion to occur. Putting it in neutral negates this effect, so the EFI has to inject fuel to keep the car at idle rpms,

PM-Performance

iTrader: (2)

One question. . . . WHO CARES? Are people going to roll down hills in nuetral all the time to save gas if this is the case?

I1DER

I look at it as any time I'm moving and in neutral, I have less control over the car. It may save gas, but so will wind slipping behind a Greyhound bus. If the bus brakes you're screwed. If you need engine braking or power when in neutral you're screwed.

The Brickyard Rat

iTrader: (1)

To save a dimes worth of gas here & there? I don't think so.

tienlo

Dont be soft. Stay in gear.

Matt8200

Im moving this post to here. Ed was trying to find proof than fuel is cut-off while you are coasting in gear.

Here are a couple of Nissan's patents:

http://www.freepatentsonline.com/4221191.html



http://www.freepatentsonline.com/4371050.html

roast

iTrader: (2)

Since my comments started this debate, let my comments end it as well.

Coasting in neutral wastes gas. This is assuming you have fuel injection, which if you're driving a 350z, I sure hope you do.

"Oh, you're wrong! Stop creating myths! We all know there is more noise coming from the engine. The engine must be using more gas than at an idle!"

Fiction. How many of you know what engine braking is? How many of you know that engine braking is also known as compression braking, and that the two terms can be used interchangeably? How many of you know what a jake brake is, and that it operates on the same exact principle of compression braking? Anyone who has heard a jake brake, will know they are loud as hell. They use no gas. The noise created is a byproduct of COMPRESSION, not combustion. The same thing applies to our cars. Need a demonstration? Find a straight road. Accelerate to about 40mph in second gear and then let off the gas. Listen to the engine. Now turn the key off. Yes that's right. Turn the ignition off. What do you notice? Absolutely NO change in sound. Step on the throttle. Nothing happens. Now you can turn the ignition back on, and consider it a lesson learned.

"What about the higher RPM? Since the engine is turning faster, it must be using more gas!"

Nonsense. An engine that is using the vehicles kinetic energy to keep it turning does not also require fuel to keep it turning. This is one of the several advantages to fuel injection(it is more efficient, it is electronically controlled rather than controlled by a "dumb" mechanical device (carb)). An engine that is idling in neutral requires gasoline to keep the engine turning. When idling, there are no external forces keeping the engine turning, therefore the ECU must supply fuel. Here is a simple way to demonstrate. Get on level surface in first gear, accelerate to 4k RPM and let off the throttle. You will slow down thanks to compression braking. Once your RPM drop to idle, you will literally feel the engine kick in. That "kick" is due to the ECU saying...hey... the engine is about to die, I better supply fuel now, because the idiot behind the wheel doesn't know how to drive. BTW don't make a habit of lugging the engine.

Hell, if you want to get cute, you can even use the MPG gauge, if I haven't supplied enough proof. Find a long gradual hill with no traffic (as to not **** people off). Start coasting down in neutral and reset the gauge. Do not touch the throttle until it registers. Take note of the MPG. Now go back and do it again. This time engine brake and reset the gauge. Don't touch the throttle until you get a reading (don't let the RPM reach idle or you will have to find a steeper/longer hill to test). Take note of the MPG. Compare the two. Consider it another lesson learned.

Have I made my case? If you need to prove it to yourself, be my guest.

Thank you, and come again.

Matt8200

If fuel is cut-off while coasting in gear, we next need to determine how much fuel can be saved by coasting in gear. This will be the fuel consumption used while idling. It should also be noted that this technique only works when you have to slow down (you would be using your brake if you were not engine breaking).

I searched for how much fuel is used while a car is idling and found this page measuring .55 liters/hour for a 1600 cc 4-valve 4-cylinder engine. Since a 3.5L engine is 2.2 times larger, I will increase our estimate by a factor of 2.2. Converting to gallons/hour we get .32 gallons/hour.

So there you have it folks, theoretically you can save .32 gallons of gas for every hour you engine break instead of coasting in neutral and breaking.