Hi, everyone. I have a question about driving technique. I drive an automatic sedan and have about a half-hour commute to work. I’ve been thinking about how to maximize my gas mileage and suddenly had a brainwave: about four or five miles of my ride each way are downhill. I can simply shift out of drive into neutral and coast for up to a mile at a time without going faster than I normally would and also without needing to use the brakes to slow down. At the bottom of the hill, I simply shift back into drive and the engine seems to pick up without any problem. I have heard that this is illegal (but don’t know why it should be) and also that it is bad for the car (but have not been given any good explanation as to how or why it would be). Is there a particular reason or set of reasons why it might be bad for the car and, if it is illegal, why? Thanks!!
In Georgia, where I live, coasting IS illegal. Basicly the reason why is without the transmission engaged to control the vehicle speed and all the wheels freewheeling, it is very easy to lose control over the speed of the vehicle. Before you know it, you are at a significant speed and the transmission is not there to provide resistance to help slow the vehicle. You are basicly putting all the weight and momentum of the vehicle on just your brakes. Coasting is not going to save you any significant amount of fuel but it can and will put undue stress on your brakes which is a safety issue.
Freewheeling, or coasting in neutral is against the law in most states. Modern-day computerized fuel injected vehicles automatically adjust for efficiency, so you won’t notice any appreciable savings in fuel by driving like this. All it does is heat up your brakes. Also consider the fact that by doing this you’re going from at least 2WD to 0WD. You never know when you’ll need the engine’s power, which you won’t have by being in neutral needless to say. So don’t do it. This is also what they teach you when driving standard transmission, using lower gears on hills keeps speed under control without causing brake fade. Good luck.
With an automatic transmission, there is little drag when your foot is off the accelerator pedal. Therefore, there is no advantage to shifting into neutral.
With a manual transmission, there is significant drag even in the highest gear. Therefore, you can save some fuel by shifting into neutral.
I assume that you don’t need the brakes to keep down to a reasonable speed. If you do need them, it is better to take advantage of engine drag. With either an automatic or a manual transmission, shift down low enough to maintain a reasonable speed without using either brakes or accelerator.
Coasting is usally illegal. One reason, which predates automatic transmissions and disc brakes, is that the car is more likely to run away with just the brakes to hold it back. The other is that, if you suddenly need power, there is a delay while you shift into gear. Coasting, by itself, will not hurt the car.
Not only is it unsafe, but shifting in and out of drive will add more stress to your drivetrain. It won’t be noticeable, but over the life of the car it will shorten the life of your transmission.
Also, it won’t save you any gas on a modern car. The fuel injection systems that have come on practically every car since the mid-80’s will completely shut down the fuel injectors when you’re riding down a hill in gear-- the momentum of the car keeps the motor turning. If you put it into neutral, the engine has to use fuel to keep the engine idling. It’s a very small amount of fuel, but it’s probably more than you’d save coasting in neutral.
i think this is both illegal and dangerous and the savings are questionable. in neutral you have the maneuverability of a rolling ball so your ability to respond to the unforeseen is zip. you also have to figure in the added wear of brakes.
i had a car, a 90’s era SAAB, that was built to do this with a freewheel that would disengage with pressure on the throttle. nice feature but it was a weak point in the transmission.