OT: Saving gas...

[Kevan]

So the debate in the car (automatic transmission) ride home last night was: Does placing a car in neutral, while coasting downhill, use less gas than leaving it in gear. Does the noticeably lower RPM mean less gas consumption? Dad says, "No, the savings are in our behavior during starts and stops." The others in the car recognize his point but think coasting in neutral too increases tank life.

What's your opinion?

[Gothard]

most cars cut the fuel supply when coasting above idle. My 1988 MB does that. So leaving it in gear and not touching the gas pedal allows for zero fuel consumption downhill

[johnnymossville]

So the debate in the car (automatic transmission) ride home last night was: Does placing a car in neutral, while coasting downhill, use less gas than leaving it in gear. Does the noticeably lower RPM mean less gas consumption? Dad says, "No, the savings are in our behavior during starts and stops." The others in the car recognize his point but think coasting in neutral too increases tank life.

What's you opinion?

I believe most fuel savings are in controlling your starting and stopping, but,... coasting definitely saves gas, especially on a manual transmission. I used to do a lot of long distance commuting by car, over 100 miles each way, and coasted down every hill on the interstate. I have no doubt it saved a lot of gas. I'd get over 50mpg regularly using that method.

It's just like riding a bicycle, maintaining speed is key. violent accelerations and stops are wasting energy.

[Lincoln]

...is that cars with fuel injection will actually stop sending any gas to the engine if the downhill is steep enough. The engine is still turning over but no gas is being used so this would yield even better mileage than neutral (where the engine would be using a small amount to idle).

[Lifelover]

It's completely analogize to what wears me out on a bike.

Quick acceleration are the most draining.

A increase in speed has a exponential impact.

Smooth out your accelerations and use Cruise control at the speed limit.


I'm not sure how stopping quickly or slowly would have much impact.

[Kevan]

I see in both our cars, a manual Jetta and an Automatic Hyundai, the tac settle down after shifting to neutral.

I also appreciate that it can be dangerous to shift a car out of drive, traffic-wise, but that's for another discussion.

[johnnymossville]

I'm not sure how stopping quickly or slowly would have much impact.

I'll give you a good example. Say there's a red light up ahead, slowing by coasting up to the light improves your chances of rolling through the light rather than being under power up to the light, stopping, and having to accelerate out of the light, therefore wasting gas. There are other examples too, like when following another car, etc,...

It all adds up to ALOT of mpg's over time. At least for me it does.

[false_Aest]

I seem to remember reading something about this on the hypermiling page.

http://www.hypermiling.com

i think its there somewhere

[RPS]

What's you opinion?Incomplete question.

[RPS]

most cars cut the fuel supply when coasting above idle. My 1988 MB does that. So leaving it in gear and not touching the gas pedal allows for zero fuel consumption downhillBut zero fuel consumption during downhill "may" not always be the most economical, right?

[Fixed]

I am saving for a bunch of cats that drive suv so I am riding through knee deep water today ..when I ride through that stuff i always think it is sewwer backup
cheers

[thejen12]

So the debate in the car (automatic transmission) ride home last night was: Does placing a car in neutral, while coasting downhill, use less gas than leaving it in gear.
I know a guy who did this in a new Saturn, and after some time (2 years, I believe), his transmission went out. The mechanic said it was because he put it in neutral when coasting downhill.

Jenn

[false_Aest]

speaking of gas....

Oil just hit $140 barrel.

[Kevan]

But zero fuel consumption during downhill "may" not always be the most economical, right?

if there's an uphill following the coasting, the driver probably would be better off increasing his speed, and momentum, so the motor is less taxed getting over the next rise. Terrain dynamics count.

I agree too that performing this action using an automatic is likely more taxing on the transmission, but a standard and a good clutch...I can only see some benefit if the driver knows what to expect with the road and traffic ahead.

My typing and brain engagement is much like a worn transmission.

[Crazy Chris]

I second the recommendation not to put an AT in neutral downhill. My Subaru Owner's Manual says putting it in neutral may harm the transmission. I also second using cruise control when surrounding traffic is no problem. When all else is at a loss, bicycle everywhere.

[RPS]

if there's an uphill following the coasting, the driver probably would be better off increasing his speed, and momentum, so the motor is less taxed getting over the next rise. Terrain dynamics count.Exactly, that's one example. If the engine is gasoline (spark ignition), it will have a significant amount of braking even when the fuel is off, so the car will slow down more than necessary if left in gear.

In some cases it may be more effective to convert the car's potential energy to kinetic energy as a form of crude storage. Just like we do on bikes. Even if not followed by a hill, the added speed will help to keep the car moving forward when on flats too.

You'd have to estimate the amount of energy that can be stored in the form of kinetic energy and determine how much of that you can recover versus how much extra energy the engine would use while idling.

It's too complex for me to know the answer. If it were a stick shift and didn't have power steering or power brakes, I'd say place the car in neutral and turn the engine off. That's the best of both worlds (provided the hill wasn't so short that the engine would require more gas to restart).

Or you could spend the 2 cents worth of gas and enjoy the drive. ;)

[Lincoln]

i just like the "feel" of coasting. but i have serious gravitational issues.

[torquer]

Smooth out your accelerations and use Cruise control at the speed limit.
I've shared that cruise control advice myself, but, maybe depending on transmission type or the sophistication of the CC electronics, its value in hilly terrain may be limited.

I got to thinking about this during a recent interstate trip in the wife's automatic-equiped car. (My car is a manual.) Using the CC, the transmission would occassionally kick down on hills to maintain the set speed; driving without the CC engaged would have allowed us to slow down ever so slightly on the hills (and accellerate on the downhills) and, I suspect, use less gas.

Obviously, traffic needs to be light enough so you don't annoy following drivers, and the net mileage increase may not be worth the bother in any case, but its worth thinking about when significant grades are on your route.

[Tobias]

I've shared that cruise control advice myself, but, maybe depending on transmission type or the sophistication of the CC electronics, its value in hilly terrain may be limited.I agree 100 percent. On hills I rarely use my cruise control on cars with smaller engine.

It's normally more fuel efficient to allow the engine to remain in a slower RPM range by having the transmission in a higher gear even if it requires the vehicle to slow on the uphill. You can make it up on the downhill and the extra time is minimal. Provided traffic allows it of course.

[RPS]

Just heard Americans are driving across to Mexico at border towns to fill up.

That’s creative, and a little funny -- or sad. Can’t decide.

[WadePatton]

Since my runs involve very little stopping/starting, I have realized a 20% fuel economy increase by simply driving slower--slower than the speed limit in many places. 50-55 is my top speed now unless I get on 70mph highways with traffic and then I'll do 65.

Cruising along at a given speed is what I do the most of, hence reducing the power requirements in that frame have produced really cool results.

I never use cruise, too many hills.

Coasting time is tiny relative to cruising time in my travels. The benefits are minimal.

Now in the good old days, I'd shut my truck off and coast--to sneak in at night.

[Kevan]

Now in the good old days, I'd shut my truck off and coast--to sneak in at night.

just be careful of what's going on in the driveway.

[Steelhead]

I just came from the drive thru teller at the bank. Whats the best to do there....cut the motor or let it idle?? I have always been told that restarting an engine sprays more fuel than a short idle and therefore uses more gas. :confused:

[RPS]

I just came from the drive thru teller at the bank. Whats the best to do there....cut the motor or let it idle?? I have always been told that restarting an engine sprays more fuel than a short idle and therefore uses more gas. :confused:IMHO if your ultimate goal is to save money I’d let it idle if not for too long a period.

Once the engine is up to temperature it won’t require that much more gas to restart, but there are other practical limits. Much of normal engine wear comes during starting and stopping, so what you may save in gas you may spend on repairs if the number of start-stop cycles are excessive for the amount of idling fuel saved.

From fuel consumption standpoint only, it makes sense to shut off sooner than what I describe above. Hybrids do it to save fuel, so I’m sure auto engineers have confirmed it makes sense.

[Lincoln]

just be careful of what's going on in the driveway.

"at least i had mine surgically removed"

[Lincoln]

I just came from the drive thru teller at the bank. Whats the best to do there....cut the motor or let it idle?? I have always been told that restarting an engine sprays more fuel than a short idle and therefore uses more gas. :confused:

according to these guys, shut it off:
http://www.consumerenergycenter.org/myths/idling.html
http://www.dailyfueleconomytip.com/driving-habits/follow-up-to-turning-your-car-off/

[ergott]

Maintain your momentum through turns. It's more economical and a blast to do.

:beer:

[Oirad]

I am saving for a bunch of cats that drive suv so I am riding through knee deep water today ..when I ride through that stuff i always think it is sewwer backup
cheers

Yeah, but Fixed, you can't coast so you won't save gas ...

Oirad