Can I save gas coasting down hill in neutral (manual transmission) instead of just taking my foot off of the accelerator while in gear? (I appreciate the associated risks while coasting down hill out of gear>) Just wondering.
You can save even more gas by turning the engine off (which some hybrids do)…for the average car neither appears in the owner’s manual of any car I know of as a means to save gas.
True, but doesn’t that make steering and braking a lot harder?
Is the 28 cents you may save on a really big hill worth it. Excessive brake wear, missed shifts going back into gear, losing control after over heating the brakes. All the a fore mentioned can cost a lot of money to fix. Will you save enough on gas to even cover a simple brake job. I doubt it. But what the hell it’s your car, I just hope I am never ahead of you on the downhill side.
Good points. I normally pump my brakes with intervals between pump to keep the brakes cool. Does that really work?
This topic has been discussed in this forum more often than any other topic.
In fact, I would be tempted to say that the topic has pretty much been beaten to death.
At the top of the page, use the Search function to find the myriad threads that have dealt with this topic over the past few years. Or, if you want a summary of what you will find in all of those threads…on modern cars you will NOT save gas by coasting in neutral, and will only subject yourself to added risk by not being in gear (i.e.–less control), and you also subject your brakes to additional wear and tear by not utilizing engine braking on downgrades.
Thanks for your comments. I have searched the forums but did not find the answer to my specific question “Can I save gas …?” Your answer is specific. One question more – is a 1999 Honda Accord a “modern car?”
The truth is that it depends on how steep the grade is. If it’s so steep that you have to constantly ride the brakes to keep the speed in check, then just keep it in gear. Nearly all fuel injected cars completely shut off the fuel under these conditions.
Much more common is downgrades so mild that they just only maintain the speed you were going to drive anyway. Under these conditions, if you keep it in gear, you are forced to give the engine enough throttle to match the transmission input shaft’s speed without actually giving the transmission any power. Then the choice is between the engine’s 650 rpm idle fuel consumption and the fuel consumption of the same engine with the throttle open enough to make the engine rev about 2000 or so rpm in neutral. The difference is substantial.
Here’s a forum just about this subject. http://www.cleanmpg.com/forums/
It is 13 years old, so lots of improvements in newer cars aren’t incorporated in a '99 Accord. Safety features such as side impact airbags, low pressure airbags, traction control, stability control etc. In my opinion not a modern car by today’s standards.
If you mean fuel injection and ABS brakes make a car a modern car, then it would qualify. You give us your criteria for a modern car, and then you can get an answer. My opinion is no. A good car, but not a modern car.
Among the scores of threads on this exact topic, here are just 4 that have arisen in recent weeks/months:
http://community.cartalk.com/posts/list/2143456.page
http://community.cartalk.com/posts/list/2146651.page
It was an attempt at humor. No one (manual) suggests you turn your car off, no one (manual) suggests you shift into neutral.
Most modern cars turn all fuel to the engine off when the car is coasting faster than idle speed with the transmission in gear will totally shut off all fuel to the engine. This generally will save more fuel and not cause safety issues. Even for the older cars, it just is not worth the tiny mileage gain.
That would be true if they ever invent an engine that has zero engine braking when the throttle is closed. With the mild grades I was talking about, you have to give the engine a small amount of gas just so the engine will let the car coast. In that situation, it is not burning zero fuel.
This is especially true with manual transmissions which. unfortunately, often have a rather low fifth gear compared to the tall overdrives offered in today’s automatics. If you have an automatic that cruises around 1600 rpm at 60 mph in overdrive, there is little engine braking when you lift your foot off the throttle, you for all practical purposes are coasting in neutral. This is why I never bother to shift an automatic in neutral on a downgrade.
Let’s try this again…
Things you can do to save gas that aren’t recommended by ANY manufacturer that I know of for various reasons…
-turn the motor off while going down hill
-run on bald tires
-over inflate your tires
-shut your car off at every stop
-never drive with passengers
-remove all extra weight including spare tire and tools
-never stop at stop signs/lights to conserve momentum
-and perhaps coasting in neutral
Let’s try this again…
Things you can do to save gas that aren’t recommended by ANY manufacturer that I know of for various reasons…
-turn the motor off while going down hill
-run on bald tires
-over inflate your tires
-shut your car off at every stop
-never drive with passengers
-remove all extra weight including spare tire and tools
-never stop at stop signs/lights to conserve momentum
-and perhaps coasting in neutral
Yet, they contradict themselves by designing hybrids that have computers that detect when the car needs zero power to maintain speed and shuts off the engine and lets the car coast under those conditions.
Of course, no car manufacturer is going to recommend coasting in neutral or with the clutch disengaged, its a CYA thing in this lawsuit crazy country.
Most every gun maker also warns not to shoot reloaded ammo in their guns, yet they sell gunpowder and reloading components, only to be used in their competitors guns I guess. CYA!!
Nobody, not even me, has ever recommended freewheeling down from the top of Pike’s Peak. I simply disagree with the premise that coasting is always dangerous. I also disagree with the premise that coasting never saves fuel.
“That would be true if they ever invent an engine that has zero engine braking when the throttle is closed.”
Well if you don’t have a throttle … 
Drove my friend’s BMW 3 series once, which uses variable valve lift in lieu of a throttle. There was an unusually small amount of engine braking. My relatively archaic 4 banger had much more engine braking when shifted to a low gear. Both of our cars are manual so it wasn’t torque converter slip.
I simply disagree with the premise that coasting is always dangerous. I also disagree with the premise that coasting never saves fuel.
I fully agree with what you’re saying B.L.E.
Things I’ve considered saying before, but I lack the will to argue against the dogma on this forum.
I simply disagree with the premise that coasting is always dangerous. I also disagree with the premise that coasting never saves fuel.
Is anyone really saying that? Or rather, are they saying that coasting can expose dangerous situations which don’t warrant the small amount of fuel it saves?