You are approaching about 2 miles of downhill but not too steep or curvy going 60 mph, no lights or stop signs at the bottom, in fact the road starts to ascend again. In neutral, you would max out at about 70-75 mph. Do you keep the manual transmission in gear or coast in neutral?
Why? Whether in gear or in neutral, I have complete control of my steering and braking. On moderate hills, I can maintain the speed limit in neutral too. What's the danger?
The truth is, back in the day when cars were unreliable and ran like crap, the engine could stop running, and you might not realize you weren't getting power to the brakes and steering until it was too late. If this happened, you might not be able to react to unexpected events and maneuver the car. The other issue was that early manual transmissions didn't have synchronizers, and you might not have been able to get it back into gear.
In spite of the fact that improvements in automotive manufacturing have largely mitigated these issues, these old laws about coasting are still on the books, and while you are coasting, you don't have as much control of your car as you do when it is in gear. Yes, the danger may seem overstated, but when you drive at high speeds, you need to be ready to react to unexpected events, and you are more prepared if your car is in gear.
The point I want to make is there is no benefit to coasting in neutral. Not one. You don't save gas. You don't improve safety. You don't make your car last longer. There are, however, disadvantages. Even if those disadvantages seem insignificant, they still outweigh the nonexistent advantages.
One last thing. Each time you put the car back in gear, you are engaging the clutch. Even if you have perfect clutching technique, this will wear out your clutch sooner than necessary. You might be the kind of person who doesn't mind replacing a clutch every few years, but many of us are driving on our original clutches after decades and hundreds of thousands of miles. My original clutch is more than 11 years old and has about 187,000 miles on it. I have made it last this long by not shifting unnecessarily.
One of the major problems with coasting in N is that if you need to suddenly accelerate the car then you have to put it back in gear prior to pushing on the throttle which could be a huge risk. Also, your foot is completely off the throttle either way so why take the risk.
If you're going down a long hill, you're going to have to use the brakes to control your speed, where if you stayed in gear the engine would be doing a lot of that work. Besides wearing out the brakes faster (the wear and tear from engine braking is negligible), you risk overheating your brakes.
If your brakes overheat, they stop working, meaning you won't be able to stop if you need to.
That is why it is posted illegal to coast down hills in some places. (Between Bullhead and Kingman, AZ, for example.)
In gear,not for one second do I even consider neutral coasting (where do you think you are Talledaga?)
For good or bad at a light I will put it in neutral (with foot on brake) and I pay attention to when the light will change so I am ready to go when it turns green.
Keep in gear. When your foot is off the gas and the car is in gear and coasting no fuel is being introduced into the engine. When it's in neutral the engine is idling, and it has to use some fuel to keep the engine idling.
When slowing to s stop from typical highway/4-lane road speeds I usually keep it in 5th gear while braking and then depress the clutch when the engine drops below 1000 RPM in 5th gear which is about 25 MPH,at which point I'll be stopped in a second or two.
If you coast in neutral the motor is still on idling. To save any gas you'd have to shut down the motor which kills the power steering immediately and in one or two pushes on the brake petal the power brakes are out of order too.
Since is would be crazy to turn off the motor you don't save any gas coasting in neutral. As long as your foot is not on the gas petal the motor uses the same amount of fuel as when it idles. Therefore you have little to no gain in mpg, and are less safe doing so.
If the OP's car is ten years old or less, then the statement "As long as your foot is not on the gas petal the motor uses the same amount of fuel as when it idles." is not true. The engine will actually use less gas (as in none at all) if the car is in gear and coasting.
The engine is being turned by the transmission (which is being turned by the wheels). When the forward motion of the car is enough to keep the engine turning at or above idle speed and the driver is not pressing the gas pedal, the engine control electronics stop opening any of the fuel injectors. There are patents on the particulars of this if you care to search for them.
Deceleration Fuel Cut-Off (DCFO) -- only on "modern" cars, that is to say, engines with computer-controlled fuel injection (available industry-wide in the U.S. 1995 and after).
Some cars, like mine, will totally cut off the fuel when the engine is being turned over faster than idle. There is no way you can beat infinite mileage. It would consumer more fuel out of gear than in.
Frankly I would not consider the possible fuel savings to be worth the bother and possible safety issues worth it.
11/04/2009 10:16:27 AM
