Just wondering if coasting downhill in neutral bad for a manual transmission? I've been reading about people who coast in neutral if going downhill to save on gas.

Will this ruin the transmission, clutch, etc? Will this actually help increase gas mileage?

 

won't hurt anything. Fuel mileage will improve slightly. Using the trans/engine to help slow down does save the brakes a bit, so maybe premature brake replacement. That's about it.

 

Actually coasting down a hill in neutral will use more fuel, not less fuel... When no throttle is applied while you decelerate in gear, the ECU will actually completely cut-off the fuel to the engine. It even says so in the service manual:

 

x2 on the fuel cutoff, and the brake wear is tremendous. My roommate does this no matter what I tell him and his is350 went through a set of pads in 10k..........

 

Wrong wrong wrong. Fuel mileage will decrease significantly. Break wear will increase significantly. Other problems include if you find you need to get out of the way of something big headed your way, you can't. Also, I cant imagine that essentially doing a neutral drop at speed can in any way be good for your car, it might be all that bad, but then again, it might be.

 

so the logical thing to say at this point is.... roll up n down hills all u want... just keep the car above 1050rpm

 

if you do not listen to the above posted and still do it... and you leave ur foot on the clutch = premature clutch wear...

 

So.. theoretically, putting a 6spd out of gear and into neutral at a red light would waste more gas where-as to leaving it in gear? I think I'd rather waste gas than wear out the clutch by holding it down for 30seconds to a minute at each light.

And to tzarchasm, I don't completely see anything wrong with going into neutral once the car is in motion [for a 6spd]... I see it done all the time and I admit that I do it to sometimes. And it's not that hard to enage back into a gear--as opposed to the 5AT.

 

I'm assuming you mean as you are approaching a red light, not when you are actually stopped at one?

 

no premature clutch wear bro......unless ur pressure plate's blown out....how would it wear it out if its not even engaged?

 

Don't do it.

 

WOW! People feel strongly here huh? Anyway you are only correct if you are completely off of the gas pedal! If the throttle is open even the tiniest bit fuel cut-off does NOT OCCUR and therefor neutral WOULD use less gas. Whatever, you are correct about the closed throttle situation... FWIW

 

how much less gas are we talking about. come on guys what the hell are trying to save 10 cents.....

 

^ hey, by tomorrow it could be 11 cents?

I think people lately are forgetting the thrill of driving, and now are focused more on saving cents... That's just torture.

 

While what you are saying is true, in what circumstance would you need to use gas while going downhill unless you are trying to accelerate, in which case putting it in neutral is not going to help you either.

 

Like I said in my post you are commenting on, I don't know if its bad for your car or not, but I am sure it is not good for it.

 

thanks for the post guys, i agree about the brake prematurely wearing out due to no help from the transmission. However if you are not going to be coming to a stop for example on the highway and you are on a highway full of hills can't you just neutral coast down them? I know there is a safety issue just curious about what an article i read and a conversation with a co worker.

As for the fuel cut off when your off the gas but in gear, that will cause the car to slow down so your still going to have to apply some gas in order to get the car going at the correct speed.


Also i've been told to coast to lights when coming to a stop instead of downshifting to prolong the life of my clutch so isn't this essentially the same thing?

Any more thoughts?

 

If you are going down a hill but want to maintain some exact speed, and the grade of the hill is too low to have to use the break, putting it in neutral is also going to lower your speed, in which case you are going to have to put it back in gear, apply some gas, then take it back out of gear again, several times per hill. The car is going to recieve much more of a slowing effect from the wind and rolling resistance than it does from you coasting in 6th gear. Therefore, on hills where you have to apply the break either way, it is obvious that you keep it in gear. On hills where you don't have to apply the break, it is less obvious, but you still want to keep it in gear since if the grade of the hill is that small that you are not overcoming resistance in 6th gear, you are not going to overcome it in neutral either.

I will allow that maybe there is some hill somewhere, with the perfect characteristics that would allow you to maintain the exact speed you want while in neutral, on certain days of the year, when the wind is blowing the correct direction, and the temprature is just right, but on every single other one of the 99.999999% of the hills in the world, leaving it in gear is going to save you more gas.

 

might aswell just shut the car off completely.. this goes back to that other thread about shut off while waiting at prolonged red lights...

ps. I wouldn't do it... downhill with no power steering and no power brakes

 

What if you don't want to maintain the speed?, obviously going down hill will make you gain speed because of the momentum you are carrying, gravity, and because the transmission is not slowing you down, the wheels are spinning freely. I think that if you are driving down a highway that has a downward slope for lets say 1.5 miles, the amount of speed (within reason, not excessive speed) you pick up going down that should allow you to coast a little further which would require you not to use the gas at all and just let the engine idle. The rpms would be at around 800 instead of around 2000 in 6th gear going 120km/h.

 

No power steering, but technically you'll actually still have power brakes, because you'll have reserve vacuum, but it will only be good for one application of the brakes. But otherwise yeah, physically turning off the engine is dangerous.

 

Yeah I'm also wondering about the samething for AT. In Toronto there also of hills on a hwy called DVP. Does using help or hinder AT???

 

lol i wouldn't do this either, i've heard of people doing this due to "hypermiling". Saw a story on cnn where a guy was getting 50mpg in his 4 cyclinder honda accord automatic by doing this kinda stuff. He would also over inflate his tires to reduce rolling resistance, draft behind trucks and try to not slow down around corners. It was pretty insane.

 

The only problem with that logic, is that if you are in neutral, your engine is idling, which consumes fuel. If you stay in gear on that same hill, your engine RPM will be 2000rpm, but the fuel injectors will be off. So you will be using zero fuel if you are coasting in gear, but are consuming fuel coasting in neutral.

I highly doubt you will coast any further in neutral than you would in gear, but even if you did, you would be consuming fuel for that entire 1.5 mile segment, but if you were in gear, you would be consuming 0 fuel for the same 1.5 mile segment. (minus any difference in distance you may/may-not coast further if in neutral)

 

I don't think i would recommend it with an automatic because you can't really rev match. I'm not sure if the auto tranny in a acura tl will automatically go into the right gear at a given speed or if it will just go into the lowest one putting a lot of strain on the tranny. Also some cars use the lower gears to lubricate the transmission while the car is running so if the car isn't in drive it might not lubricate the tranny causing excess wear and heat. It is also like neutral dropping the car into drive which is never good.

Another thing is that some cars can not be flat towed which might be the case with the tl not sure. If it can't be flat towed then you should not put the car in neutral while the car is moving.

 

makes sense, thanks and i agree that this is the case in some instances.

 

Coasting in neutral is illegal in Virginia (Va. Code 46.2-811) and the points stay on your record for three years. I don't know about any other states, nor do I know how they would enforce this law as a practical matter.

 

In what instances would it not be the case? The 1 in a million hill I referred to earlier? Other than that I can't think of any.

 

For instance when it is a slight grade and being in gear will actually cause more resistance and require gas and being out of gear will just let the momentum of the car carry it down requiring no use of the gas pedal. Give it try. The wind resistance your talking about it negible since you aren't going to be faced with hurricane winds.

 

Wow this thread is evolving into more pointless arguments...

Throwing a car in neutral, while going down the slope...out of no where a punk kid races in front of you, you need to accelerate to avoid him..... oops, you didn't make it.... yei, but you saved a few pennies.

I only throw neutral when parking, to roll to a stop, before throwing in reverse.

 

I think if someone accelerated out in front of you, your reaction would be to slam on the brakes not accelerate even more.

 

^^^ That's a girl reaction....

I steer away from trouble. But then again driving courses and track time might be of use to you as well...

 

How you figure thats a girl reaction, living in a city you don't really have room to steer away from action. You got cars everywhere, on coming traffic, pedestrians, where are you going to steer to? Different situations call for different methods.

Also your comment about me needing track time, if you don't like this thread stop looking at it. This forum is here for people to discuss things and ask questions. I've been looking at other threads and people are quick to start slamming and flaming people for asking a question. Whats the point of having a forum if you think you are going to be flamed? People should be able to discuss and ask what they want with out having people like you making dumb comments.

 

^^^ I have a full right to disclose my dumb comments, before everyone attempts to argue with a service manual and people that know TLs inside and out.

And thank you for enlightening me on what a forum is.

I'm not here to argue. But I will dispute stupidity when I see it. Don't get me wrong, hypermiling also works, but it is also a stupid and a dangerous practice...

 

If you are being a tard, and leave the transmission in 1st gear, push in the clutch, then coast down a hill in anticipation of needing to be in first gear at the bottom of the hill to ascend another steep hill....

With the clutch not engaged, and the transmission in gear, the clutch plate will still spin at whatever the input shaft speed is... If you are in low gear as you are coasting down a hill at say 70mph.... Your input shaft will be spinning at an insane speed. (imaging driving 70 in first gear). Your clutch will fly apart.

I've seen it happen on off-road vehicles before. Granted, your clutch won't "wear out" in this case, it will just self-destruct....

 

And thus you want to throw in neutral around all of those obstacles?

(I live in NYC, I know what traffic is)

 

First i didn't think my question was stupid, all you had to do was answer the question and leave your dumb comments out of it. If you thought it was stupid, why waste your time answering it.

Second if you read the post i said on a highway. I didn't say neutral in the city. I know it is unsafe thats why i said i was curious after i read an article. I don't do it.

Third you are the one saying you want to steer out of the way "around all those obstacles" when the safe thing to do would be to brake in a congested area like the city.

I'm not here to waste my time arguing with people like you. I just was curious about this subject. So if you have something to say about the orignal subject then go ahead. Other than that don't waste my time with your immatureness.

 

^ is this kid for real?

I did not refer to your question as being stupid. What's stupid is arguing with a service manual which tells how the ECU/PCM is designed to save you gas. My comments are directed at the thread, not grsd03.

You need to read posts carefully...as you are successfully confusing yourself.

Be safe.

 

so far we have:

Pro: you may save a little gas

Cons: brake usage will increase, throw-out bearing may go, unsafe, etc...etc....

Coasting in gear makes much more sense (avs007), in other words, just drive in the right gear, let the technology do the hard work for you.

 

Well, I guess that depends on the grade of the hill and physics. Sometimes you need to accelerate a bit just to maintain your speed. Leaving the transmission in gear without touching the throttle also brings in the element of "engine braking".