[Auto Talk] Can regularly shifting to Neutral on an automatic gear damage it?

Discussion in 'Lounge' started by Adrian Wong, May 14, 2008.

  1. Adrian Wong

    Adrian Wong Da Boss Staff Member

    Hi guys!

    I have an automotive-related question for the gearheads in this forum. :beer:

    My car has a 4-speed automatic transmission and I regularly shift to Neutral whenever I go downhill to let the car coast and save a little petrol.

    Of course, engaging the auto transmission after that can sometimes cause the engine to rev up suddenly. So I normally tap the pedal a little to rev the engine before engaging the auto gear.

    Someone recently told me that doing so will damage the automatic transmission. Is that true? Thanks! :beer:
  2. wiiz

    wiiz Just Started

  3. zy

    zy zynine.com Staff Member

    i think this doesnt really apply to modern cars.
    modern cars have advanced ECU, they should minimalize fuel compsumtion while you are coasting downhill. besides, while coasting downhill in neutral, your car engine still uses fuel to maintain the rpm even if you are in neutral.
  4. Chai

    Chai Administrator Staff Member

    I think it's better to leave the gear in D while the car is moving, because you are not using more or less fuel as long as you are not on the pedal.

    Unlike manual cars, when your car is engaged to a gear, especially at high engine speed, your car will slow down even on a down hill slope. That's the reason why some like to shift to neutral, but it's dangerous.
  5. PsYkHoTiK

    PsYkHoTiK Admin nerd

    I wonder how much the torque convertor would like that.

    Coasting is bad practice IMO.

    Just how much can you save anyways?

    Plus coasting in gear may actually save you more gas (foot off throttle, the gas mixture usually cuts back as opposed to idling its still on).

    Plus engine braking wont wear out your brakes as much (aka coast in gear).

    Coasting in neutral is dangerous... :hand:
  6. Adrian Wong

    Adrian Wong Da Boss Staff Member

    Actually, coasting in neutral can save a LOT. In city driving, I went from 8.5 km/l to about 10.5 km/l. On the highway, I went from 10 km/l to about 13 km/l.

    The thing is I have no idea if it's bad on the transmission.

    As for safety, I don't see how it can be a problem because I treat it like a manual shift. In the sense, I can shift out of neutral pretty quick (my hand is always on the shift stick).
  7. PsYkHoTiK

    PsYkHoTiK Admin nerd

    Coasting in gear with the throttle closed (aka foot off the pedal) closes your fuel injectors (aka not using fuel at all). Most of not all modern fuel injection systems cut off the fuel if not most of it while coasting in gear. However, it is not so when you are in neutral.

    Coasting is dangerous as the balance of your car is affected (try cornering with your car in neutral). It is a good reason why they made it illegal in some places. Not to mention in an emergency, you have much less reaction time (now that you have to get back in gear).

    As for your tranny, your torque converter will not like you.

    Plus with coasting you use up more of your brakes (tranny is a low wear component). I always engine brake when possible (and coast in gear).
  8. Chai

    Chai Administrator Staff Member

    Very bad for torque converter. :D Coasting in free gear is dangerous like I said earlier, and you shouldn't save fuel by going into neutral unless your foot is on the throttle.
  9. Adrian Wong

    Adrian Wong Da Boss Staff Member

    I just tried going downhill without coasting. The engine revs at about 1600 RPM (instead of 800-900 RPM at neutral) and I actually have to press the pedal to keep the speed up. In neutral, I actually pick up speed and the engine revs at a much lower speed.
  10. Mac Daddy

    Mac Daddy Pickin' Da Gitfiddle

    You will save some petrol doing that Adrian but as mentioned your transmission and torque converter aren't designed for it. So over time you will shorten the life of your transmission. I coast in neutral quite a bit but I drive a 5 speed standard so its a bit different.

    Same goes for people racing around using L1, L2 and Drive without a proper shift kit. Its not designed for it.
  11. Adrian Wong

    Adrian Wong Da Boss Staff Member

    Hmm.. In that case, I better lay off the transmission!! :haha:
  12. Chai

    Chai Administrator Staff Member

    When the engine speed is at 1600rpm, that's because the gear is engaged, it doesn't mean you are consuming more fuel than neutral. You can only really save fuel if it's a very long slope, or the slope is not really steep enough for the car to coast in gear, like what you have just said, needed to accelerate to keep the speed.

    Last edited: May 14, 2008
  13. Adrian Wong

    Adrian Wong Da Boss Staff Member

    Yup, I know that... but you can really feel the engine drag. Instead of accelerating downhill (when in neutral), I actually have to pump gas to maintain the speed.

    But if switching back and forth from neutral is bad, I guess I will restrict it to only times when I'm sure I'm coasting to a stop.

    I actually thought it would be okay as the transmission automatically selects the appropriate gear (3rd or 4th) according to the speed when I shift the transmission back on.
  14. generalRage1982hrv

    generalRage1982hrv ARP Reviewer

    hmmm nice shifting hahhahaha
    anyway you can damage your gear box but you will not gain any fuel saving
    when you go down the hill with normal gear without pushing gass pedal you have same shit like without a gear
    when u remove foot from gas pedal automatic fuel intake shuts down extra fuel so it is giving normal fuel flow (for working -around 850rpm)
    but inertion is stressing gear box in normal rate so engine goes wild without extra fuel lol that is proper way to do it LOL

    you all need to hear when truck do that LOL it is like someone is screwing cow lol
    Last edited: May 15, 2008
  15. rogue_tomato

    rogue_tomato Newbie

    We used to carpool, and my buddy back in school used to do the exact same thing. I asked him why, and he replied "to save gas". Which made sense... except the loud noise and/or jolt from disengaging/re-engaging gears... That just didn't sit well with me, so while I've thought about it, saving gas while sacrificing my transmission didn't seem worth it :p
  16. wiiz

    wiiz Just Started

  17. zy

    zy zynine.com Staff Member

    drive about 90kmh :mrgreen: that should be about the maximum fuel economy :mrgreen:
  18. Adrian Wong

    Adrian Wong Da Boss Staff Member

    I wouldn't want to queue up for an hour just to refuel. :mrgreen:

    Even if I want to sacrifice boot space for the tank, I will wait until more stations offer NGV.
  19. Adrian Wong

    Adrian Wong Da Boss Staff Member

    Surprisingly, I get good FC even at 140 km/h. On the highway, that gets me something like 12-13 km/l. Seems to be about the same at 110 km/h.
  20. Chai

    Chai Administrator Staff Member

    That's because you have exceeded 90km/h. Above 90km/h, you are not just using more fuel, but fighting the drag as well. You will see some improvement driving at 80-90km/h at constant speed.

    My father actually tried driving on trunk roads at 80km/h and claimed to have improved mileage. I wouldn't do that just to save fuel even knowing the fact. I just "cruise" at 110km/h on highway.
    Last edited: May 15, 2008

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