Shifting Into Neutral To Save Gas

[DaSwede_420]

I was just wondering if it is harmful for the transmission to shift into neutral

(on an automatic) for coasting down large hills. I dont think it's harmful at all, but my mom argues that it wrecks the tranny.

thanks!

[GuyTelefunken]

Not particularly harmful but not recommended either. It's pointless I.M.H.O. It is more appropriate to shift into 4th. or 3rd. while going down a hill. The engine uses approximately the same amount of gas when running down a hill in a lower gear as it does while idling in neutral. As well, the extra wear and tear on the brakes and rotors by using them to slow the car while going downhill is unnecessary.

[SW03ES]

Its also illegal in many states.

[SRK]

A few things come to mind.

The PCM probably switches off the fuel on decel above a set RPM, and this would occur when the trans remains in TC lock-up. When you press the brakes, you may feel a slight bump in the drivetrain, which is the TC coming out of lock up. As the engine RPM slows the PCM begins to add fuel, and the overrunning clutch in the trans allows a lower RPM for the road speed. All this is very subtle in these cars.

Coasting in neutral is illegal for sure still, although the reasons make no sense in today's automotive world. It is from the days when cars had non synchronized manual transmissions, and like many other laws a hold-over from old times. Can't really apply to most automatic trans anyways.

Leave the trans in drive and be done with it. There are far better ways to save fuel.

[bartkat]

Coasting in neutral, you don't have total control of the car. Even with automatics, in a panic situation, a person might be unable to put it in gear, or a least not quickly enough for an evasive move. As I understand it, in overdrive, a car is freewheeling when coasting anyway if it's not on cruise control. And there lies another problem. If you're in neutral, what's gonna happen to the cruise?

[Wicked_Lex]

I agree with the others. If the tranny is in 'D' and you’re going down hill with your foot off the gas you aren't going to use much more fuel than idling. And, as others have said, coasting in neutral is illegal as well as dangerous. The best way to save fuel by coasting is to take your foot off the gas when you are a block or two from a stop light/sign in the city and a ¼ mile on the highway instead of gassing it and braking hard when you get there.