Have a 2.4L auto. When on a long hill and not using the accelerator the revs are much higher than if in neutral. Does putting it into neutral: save/use more gas? cause harm to anything (like if moving at speeds >60km/h)? Also do the answers differ if on flat vs downhill?

 

in neutral it has to idle. on a down hill and not pushing on the accelerator it isent useing any gas

 

wont harm anything but i doubt ur saving any gas our comps automatically compensates for the best possible fuel economy

 

how high the rpms are is not the only deciding factor. especially when you're letting off the gas. with an auto, there's not too many things to consider, but just leave it in gear and let off the gas pedal.

 

Are you trying to hypermile or something?

 

I know in NY it is illegal to coast in neutral because you wouldnt be able to power out of an accident if you saw one coming.

 

well, this is the hypermiling forum

 

ic, thx all

 

Today's cars have a "fuel cut-off". If, for example, you're driving 50mph, and you see a streetlight in the distance turn yellow, from the point you lift off of the throttle, regardless of RPM, the fuel injectors will turn off. Placing the car in neutral requires the car use fuel to keep the engine speed at idle, is potentially dangerous, and in most states illegal.

 

I have been driving in neutral a lot and when I do my MPG reading goes up a pretty good amount. Is the meter not very accurate or what? Should I stop doing this completely?

I have an automatic 08' Sport btw.

 

I've noticed my DIC on AVG. is off my 1 MPG or so. My actual is usually a little worse. Ive just filled up with Shell 98 octane and seem to be getting better milage. I'll have to see if its actually getting better by actually calulating my milage. I have a '08 2.2L

 

i'm assuming you meant 93 octane? if so, don't waste your money. you will not get any better mileage. may even be worse. it's all ricer myths that higher octane improves mileage. just use regular 87.

 

qft.

 

The higher octane just tells you that the gas is more resistive to detonation (aka, knock retard) If you're not boosted or have smaller pulleys stick to the 87 or 89.

"The octane rating is a measure of the resistance of gasoline and other fuels to detonation (engine knocking) in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design."

Thanks Wikipedia: http://en.wikipedia.org/wiki/Octane_rating

 

When coasting in neutral, the engine will require fuel to keep it running. Leave it in gear and let off the gas, the engine uses ZERO fuel, the momentum of the car keeps the engine turning.

Not to mention that once you have "coasted" down you need to get back up to speed....put the dic on instantaneous mpg and watch what happens to your mileage then . Much better to maintain a steady speed than coast, gas, coast, gas....

Big secret.....brakes use gas! Every time you step on the brake, the fuel you burned getting up to speed is turned directly into heat by the pads / rotors. If you can train yourself to be aware of not only what is right in front of you but what is farther down the road, you can let off the gas and come to a stop with almost no brake at all. Saves (a little) gas, saves brakes....of course, you want to be doing this where traffic allows, don't be an ass just for the sake of 0.05 mpg

Bottom line, drive like there are raw eggs taped to the pedals and you don't want to break them. Not really exciting (ok, not at all exciting) but if you are looking to squeeze every inch out of every gallon.......

 

Could you explain why the DIC reads a much higher mpg when u suddenly go to neutral if uses more fuel as you say? I am not doubting what you said but im just not clear about it. Ive found different results in different scenarios

1) If I am going down a steep hill, I get better mileage (based on DIC readout) by leaving it in 5th gear

2) but if i am just rolling up to a stop light in 3rd gear, the DIC says I get better mileage if I shift to neutral and coast up to the light as opposed to leaving it in gear until I stop.

 

the fuel cutoff is simple, and is explaines a bajillion times. basically if you're over like 18mph and 1500 rpms or something like that (rpms may be a little higher) and leave the car in gear, and let off the gas pedal, you are using ZERO gas. ZERO. if you throw it into gear, you are using gas to keep the engine idling.

you should never be in neutral while you're moving though. it's a bad habit that manual drivers pick up for some reason.

 

I assume u meant to say if I throw it into neutral, it uses gas to keep idling. Yeah I understand what you are saying and Ive read lots about the fuel cutoff before.

But does this just mean that the DIC fails to account for this, since If i'm rolling in gear and off the gas pedal, I should be getting some ridiculously high MPG (higher than neutral at least)?

 

if you're rolling in gear and meet the needs for dfco you will see 99 on the dic, which is as high as the dic displays. i've tried it in neutral, and get about 40 something usually

 

I hear what you are saying and I haven't rode in neutral since... But, when I was riding in neutral at any speed over 30mph and reset my MPG meter, it said 99.9 until i either put it into drive or slowed down to a stop.

Nonetheless, I am going to continue riding in Drive and never switching it into neutral.

 

You are looking at the average mpg, kinda pointless for this discussion. Put it on inst mpg and you will see what we are talking about.

 

opps! kk i will do... waht does inst mean btw?

 

Not necessarily true, if an engine is designed to function at it's best with 93, it will not get as good of gas mileage on a lower octane.

But putting 93 in a 91 crx won't do ****...haha

 

we were talking about a base model cobalt though. i should have been more specific i guess and said higher than tuned for.

 

Instantaneous (sp?), tells you what kind of mileage you are getting right at that moment. Average mpg just shows the average since the last time you reset it.

Walk on it in 1st or 2nd and you can get into single digits on the instantaneous mpg, rolling down a hill (in gear) with no throttle applied, it will go to 99mpg....only because it can't display infinity

For what it's worth, cruising at 160 kph (100 mph) gets me about 16 mpg out of my 2.4 manual, about the same as my boss gets in his F250 at 100 kph (60 mph)