Anyone else do this while driving their 5AT?

Anyone put the selector in Neutral while coasting down long hills? I find myself doing this a lot, am I right to assume this helps mileage slightly by having the engine run at a slightly lower RPM? I know it really helps when you are going 60mph and shift into N instead of just coasting in D, but while going 30 mph does it make a difference?

You're putting extra wear on your tranny by shifting it in and out liek that. While coasting in D, you are using No gas, the engine is under compression. When you shift into N, the engine must use gas to maintain idle.

 

In other words...stoppit. It's an automatic. Put it in D anf leave it there. Or use the sportshift if you have it.

^+1, Don't do that.

^+1, Don't do that.

 

your response read in my mind like a swift smack on the back of the head...

Leave it in gear;)

what about for those with 5MT - do you leave them in gear too? I have a 5EAT but just curious.

5MT is same way, In gear and no throttle = zero gas consumption

 

Out of gear, engine needs gas to idle

5MT is same way, In gear and no throttle = zero gas consumption

 

Out of gear, engine needs gas to idle

Um...

Correct me if I am wrong but wouldn't zero gas consumption only be achieved by turning off the engine? This is how hybrids work. If you read the manual it states not to coast without being in gear so that you have better braking, and in case of emergency you can accelerate faster. This is for the 5MT.

 

X

If the car is in gear, and your foot is not on the gas, then you are under compression, or engine braking. An engine uses no gas while under compression becasue the movement of the car is keeping the engine spinning. When you take it out of gear, the engine needs gas to stay idling because there is nothing else to keep it spinning.

Regardless of slushbox or row-it-yourself, it's never a good idea to "neutral coast," and in many places this is expressly illegal.

 

Why?

 

Because if an emergency situation arises whereby you actually need to modulate the throttle instead of slam on the brakes, neutral-coasting could cost you valuable seconds of reaction time, and/or may result in, of course, no response at all as you furiously stomp down on the gas-pedal, to no avail!

*face turns red* alright I really should have realized that, not that hard of a concept :/

*face turns red* alright I really should have realized that, not that hard of a concept :/

 

No need to be embarrassed - we all learn from each other, that's why we're here!

ah, so I learned something as well. So compression braking, no gas usage? that is why the instant MPG metter goes to 99.9 when you let off teh gas in a slight downhill?

 

X

B.S. about the *no* gas thing.

 

When you are coasting down a hill with your foot off the gas and the tranny in gear it is still using gas. It is squirting the same amout of gas into each cylinder as it does at idle, its just doing it 3000 times per minute, rather than 750 times. So moral of the story is you will improve mileage SLIGHTLY (almost immesaruably) by neutral coasting down hills, and, as mentioned, you shouldn't do it, but I do it for fun sometimes anyway. Actually I always do it on a certian hill becasue if I leave it in gear it takes just a tiny bit of throttle to keep constant sped and then the car does that jerky thing, so I just push the clutch in.

B.S. about the *no* gas thing.

 

When you are coasting down a hill with your foot off the gas and the tranny in gear it is still using gas. It is squirting the same amout of gas into each cylinder as it does at idle, its just doing it 3000 times per minute, rather than 750 times. So moral of the story is you will improve mileage SLIGHTLY (almost immesaruably) by neutral coasting down hills, and, as mentioned, you shouldn't do it, but I do it for fun sometimes anyway. Actually I always do it on a certian hill becasue if I leave it in gear it takes just a tiny bit of throttle to keep constant sped and then the car does that jerky thing, so I just push the clutch in.

 

in the old days, that was true with carburated engines...

 

modern fuel injected engines are smart enough to cut fuel in these kind of situations... Or so i've been taught.

One statement that caught my attention was this:

You're putting extra wear on your tranny by shifting it in and out liek that.

Every now and then at a red light, I would put the car in neutral and pull on the handbrake / e-brake (stops are notoriously long on certain intersections). Am I actually putting in additional wear on my tranny. One of the reasons I do that is that I thought I was easing off pressure on the tranny / clutch.

Using the e-brake(still in D) at traffic lights is a good technique and probably only necessary if you've been driving spiritedly or just came to a very hard/fast stop and want to avoid hotspotting your rotors.

 

Again, keep it in gear.

Langosta: You're wrong, I'm right, suck it up.

If you've ever had an AFR meter hooked up, you'd notice that it goes all the way lean when you are off throttle and coasting. It goes between lean and rich while idling and under gentle acceleration. It goes way rich under WOT.

 

 

Richip: You don't have a clutch. You have a torque converter, which is designed to work with the brake on and the car not moving while it is in gear.

 

 

If it were a 5MT, then taking it out of gear and letting the clutch out would reduce wear on the thrust bearing.

It's called an "automatic" fr a reason,,leave it alone. lol

 

Rudy

Langosta: You're wrong, I'm right, suck it up.

If you've ever had an AFR meter hooked up, you'd notice that it goes all the way lean when you are off throttle and coasting. It goes between lean and rich while idling and under gentle acceleration. It goes way rich under WOT.

 

+1, Langosta just monitor the instant and average gas mileage readings on the trip computer. Since the readings are based on the miles accumulated and IDC(Injector Duty Cycle) you can easily deduce how much gas is getting consumed.

I'd like to see something form a reputable source on whether or not a vehicle uses gas when engine braking.

Easy,

 

1. Download the TARI datalogger from http://www.tari.co.za/cgi-bin/yabb2/YaBB.pl?num=1126075051

2. Datalog the "Fuel Injector #1 Pulse Width"

Richip: You don't have a clutch. You have a torque converter, which is designed to work with the brake on and the car not moving while it is in gear.

Thanks. I just assumed that keeping it in D would cause strain on the tranny since the extreme opposite (power-braking) is said to overheat the A/T.

I'd like to see something form a reputable source on whether or not a vehicle uses gas when engine braking.

Why would an engineer design a modern vehicle to use gas in this situation? What would be the purpose of that?

If you're coasting down hill at 2500 rpm and the engine is using gas, it would also be producing power. You wouldn't get much engine breaking that way.