On Automatic Transmission do you save gas shifting to neutral at stop signs?

[Eli]

Again, I wonder about injector pulse width duty cycles at no-load idle vs. loaded idle. I'm skeptical that the engine even adjusts anything when the idle changes. If that was the case, it would make more sense for the ECU to maintain idle RPM nomatter what.

 

[Mark R]

Originally posted by: Eli
Again, I wonder about injector pulse width duty cycles at no-load idle vs. loaded idle. I'm skeptical that the engine even adjusts anything when the idle changes. If that was the case, it would make more sense for the ECU to maintain idle RPM nomatter what.

I think there is some sort of idle correction done by the ECU - same as for the AC.

I know in all recent cars that I've had, that when you switch from neutral to drive the engine speed rises immediately, then as you feel the transmission enagage, the engine drops to its natural idle speed. So the ECU clearly gets the information that drive has been selected and compensates before the transmission actually engages.

ECUs may also have inputs from AC for a similar reason - although not all manufacturers bother with this.

 

[angminas]

Originally posted by: AgaBoogaBoo

There have been long threads on this, and the simple way to do this is the following:

1. Stay in gear
2. Apply breaks
3. Keep applying breaks, as RPM's get closer to idle, bring car out of gear

You shouldn't need to use engine braking, we're just doing city driving and not on a track, right? Also, downshifting just means that you're using the clutch one extra time, that is unnecessary.

What's cheaper to replace? Brake pads or a clutch? Search around on AT, this has been covered in long threads, but basically, your brake pads are just fine for coming to a stop. Ironically, that's what they were designed to do.

How long should you wait before bringing it out of gear? It honestly probably doesn't matter a lot. You can bring it out when you feel like it - wait for it to drop to 2000 rpm, 1000 rpm, right as you apply brakes, etc.

The best post in the thread. Main points in bold. Toss in safety and the rising price of gas and that's pretty much all there is to say.

 

[B00ne]

Originally posted by: SampSon

Originally posted by: tidehigh
cmon guys...

brake rotors get hot. hot metal warps. if he heats his brake rotors a ton in a bigtime stop. he puts it in neutral so he doesnt have to keep the brake pressed upon the rotor in one spot for the amount of time that he's sitting idle anyway.

still dont get it? i dont care

And what if he needs to use his brakes to keep his car from rolling?
Park would be a better option if he REALLY needed to cool his rotors down.

Well driving would be the best thing to cool the rotors down. Anyway if the rotors were that sensitive, you could never drive down a mountain - not everybody will shift down and let the engine do the braking

 

[Dulanic]

Originally posted by: Pacfanweb

Originally posted by: Dulanic
Nope my engine stays off at stops and low speeds.

Your engine is OFF at low speeds? Care to rephrase?

Nope, it's a hybrid LOL so the engine is off at stops or low speeds when it just uses the electric motor.

 

[Boo Boo]

you put more wear and tear on the shift mechanism and if you forget you look like a ass for reving it

 

[OrganizedChaos]

go put an oscilloscope on the IAC(or equivalent) and find out.

 

[Gigantopithecus]

The only way to save gas at a stop sign is to not stop. However, all reduced fuel consumption savings will be offset by fines.

 

[randomlinh]

Originally posted by: XabanakFanatik

Originally posted by: mb

Originally posted by: XabanakFanatik

Originally posted by: mb

Originally posted by: Quintox
What about coasting?

NO.

Whenever you are driving on public roads, you should always be in gear.

What's your reasoning behind this?

Safety.

Thanks for the specific answer backed by logical reasoning. :roll:

To reiterate what was said.. pretty much common sense that if you're already in gear, you will be quicker to react.. or should be anyway.

plus, it's illegal to coast around town out of gear here. And most places I believe

 

[KPACOTKA]

Certainly you save a lot. I'd also recommend to turn engine off. So what I do, stop, neutral, off. If wait a longer than 30 seconds, then I shift to park, and release my foot.

 

[KPACOTKA]

Originally posted by: Dulanic
Nope my engine stays off at stops and low speeds.

Your engine is OFF at low speeds? Care to rephrase?[/quote]
he shuts his engine off, so he can coast with no fuel usage at all!!!

but only when going down a hill.



[/quote] Exactly. When I drive from SF all my way is down, so I shift to neutral, stop engine and use only brakes. Due tough traffic it takes about 40-60 minutes. I think even in idle for 1 hour your engine eats enough gas. I have only one problem, after 20 minutes my power brake system stops working, so I had to push harder. For this reason I need to eat more to be stronger. Do you think I waste money on food?

 

[mugs]

Originally posted by: randomlinh

Originally posted by: XabanakFanatik

Originally posted by: mb

Originally posted by: XabanakFanatik

Originally posted by: mb

Originally posted by: Quintox
What about coasting?

NO.

Whenever you are driving on public roads, you should always be in gear.

What's your reasoning behind this?

Safety.

Thanks for the specific answer backed by logical reasoning. :roll:

To reiterate what was said.. pretty much common sense that if you're already in gear, you will be quicker to react.. or should be anyway.

plus, it's illegal to coast around town out of gear here. And most places I believe

Everyone always says that, but I think the odds of being in a situation where you have to accelerate to avoid an accident are pretty low. Low enough that it's a non-issue.

 

[KPACOTKA]

Exactly. Imagine, you are at stop and notice a fast approaching car from behind, you peddle and get hit from aside.

1. it's your fault and you pay insurance
2. it's more dangerous, because can be no side airbags

There is another technique when you are preparing to stop and shift to neutral keeping moving. In this case you get more wear on your brakes and have a chance that you lose control of car.. So it can be done only in slow moving traffic downhills.

 

[Raduque]

Originally posted by: Pacfanweb
Yes, it does, because the engine is loaded when it is in gear. It takes more gas to keep the engine idling with the trans engaged than it does when the engine is freewheeling in neutral.

Think of it from a stick shift perspective: If you are stopped on a slight incline, and you can slip the clutch and engage it just a bit to hold the car still, do you think that puts a bit of a load on the engine?
Of course it does. (also wears the clutch but that's another story)

So having the tranny in gear at a stop is the exact same thing.

The reality is, though, the gas it costs you is insignificant. To say that leaving the car in gear burns more gas it technically correct, but it's not enough to worry about.

Yes, I considered that, but didn't feel the need to elaborate. Loaded at 600rpm, unloaded at 900rpm, I'm willing to lay a bet that either it uses the same amount of gas, or there's a negligible difference.

Originally posted by: bobsmith1492

Solution: drive a manual.

Except you can't get a V8 with a manual in an F150 =P

 

[angminas]

Originally posted by: mugs

Everyone always says that, but I think the odds of being in a situation where you have to accelerate to avoid an accident are pretty low. Low enough that it's a non-issue.

I disagree. This is the kind of thing people say to justify not wearing seat belts, etc. And the real issue isn't acceleration, but knowing the situation of your car and your body at all times. This is the same reason you use the right foot for both the brake and the accelerator- so you don't have to think in an emergency. By the time you think about where your foot or the shifter is, the kid is under your car, or your car is under a semi, and it doesn't matter what the odds were.

 

[GrumpyMan]

Every time I stop I put my car in reverse just in case anyone runs a red light.