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

[Adrian Wong]

Hmm.. In that case, I better lay off the transmission!!

[Chai]

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.

One of the worst things you can do to an auto trans is to disengage it from drive range and re-engage while still moving. Based on fluid dynamics, valve body pressures and solenoids you are adding much un-needed wear to the transmission.

On top of the mechanical side of it, ANY-time you disengage the engine from the drivetrain of a vehicle while moving at a good rate of speed, your stability and control of the vehicle is compromised. It is a fact that physics and various law of perpetual motion can explain to you. Why in the world are you contemplating doing this? Are you so financially in the hole that ten cents in gas will determine if you eat tonight or not? God help you, that being the case!

If you actually think about it, in cars that have an automatic transmission, and at speeds where (if equipped) you are not going fast enough to have the "lock-up" torque converter in lock-up, letting off the gas completely will slow the engine back down to idle or close to idle just the same as letting off the gas with the transmission still engaged in range "D." That is what a torque converter does, it allows a fluid coupling between the engine and transmission such that when you are not accelerating, you are breaking that direct connection between engine and driveline. It just does it such that the connection is not "hard-broken" (IE...shifter in neutral and totally disconnected) and when you accelerate, it is ready to engage based on fluid pressure, fluid dynamics and thermodynamics.

In a manual transmission I see no real wear issues with doing this ONLY if your vehicle is built so that the transmission is being lubricated when in neutral and in motion. Some are not, hence, neutral combined with motion is not a good thing. I argue that in the absence of the above, you are far more likely to lose stability and control of a manual with it in neutral and coasting down the road than in an automatic in the same situation. You all may think that premise sounds crazy, but think of it like this. A vehicle in motion is a combination of many things all encompassing mechanical balance. When a vehicle, be it manual or auto is in motion, the engine and driveline need to be connected because that is the way they were built to be operated. Gas consumption is a mute point as well as totally negligible.

[Adrian Wong]

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.

[generalRage1982hrv]

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

[rogue_tomato]

Originally Posted by Adrian Wong

Hi guys!

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

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!

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

[wiiz]

boss.. if you want save fuel, why not try NGV.
Malaysian Hijau NGV Group - Home

[zy]

drive about 90kmh that should be about the maximum fuel economy

[Adrian Wong]

Originally Posted by wiiz

boss.. if you want save fuel, why not try NGV.
Malaysian Hijau NGV Group - Home

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

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

[Adrian Wong]

Originally Posted by zy

drive about 90kmh that should be about the maximum fuel economy

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.

[Chai]

Originally Posted by Adrian Wong

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.

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.