Coasting in Neutral

I tend to like to coast down big hills and take slow stops on my long trip to work and I realized the other day that it was weird that my RPM stayed at the same level while doing this as it would if I were giving 'er gas. So I started shifting (my automatic 98 Jimmy) into neutral as I stop and the RPM's drop down significantly. I figure if I did this religiously I could make a small dent in my mileage, but I'm wondering if this is normal, or if all the shifting back and forth could cause problems. Also, when I decelerate in neutral the fuel guage plummets dramatically; it goes from half a tank to turning on the low fuel light--can anyone explain this?

Yep, you are a dreamer and slower speeds (ie lower rpms) and slower starts are biggest savers and AC off adds another 2mph usually. Short term the trans will be fine as for constantly doing this I would have to guess the trans internal pressures are dropping when you go to N then have to boost quickly and this was not a design consideration for daily multiple occurrance. I would keep the tires inflated to 35 psi and if a real issue get a small car! As for the gage, the fuel pump is nera the rear and a long tank and the level senders are a known problem in all - GM has a newer robust design (and part of the pump) so do it youself is apprx $400.

Yeah, I'm all for saving money and the environment, but I still can't give up my truck, so I'm just trying to get as much out of it as possible. I was half looking at the hybrid Escapes though...

The weird thing about the fuel guage is if I make a sudden stop in drive the needle dips two or three ticks, maybe a quarter of a tank tops, but when I make the same stop in neutral it drops from half a tank to dead empty. The first time it happened last night it freaked me right out--I thought for sure I'd look back and see my fuel tank rolling down the road behind me!

shifting from drive to neutral to drive everytime you stop is not gonna help with fuel economy and will probably cause tranny issues down the road.

Take those $.02 gas savings and put them in a high yield savings account to pay for the new tranny. And if you're coasting down long hills in neutral. are you using the brakes more to control your speed, thus increasing brake wear?
I know that some trannys don't pump fluid (thus Lubrication) in neutral. Not sure if ours falls into that category. Something to think about, are the teeny savings now coing to cost a whole lot later?

Yeah, I'm all for saving money and the environment, but I still can't give up my truck, so I'm just trying to get as much out of it as possible. I was half looking at the hybrid Escapes though...

The weird thing about the fuel guage is if I make a sudden stop in drive the needle dips two or three ticks, maybe a quarter of a tank tops, but when I make the same stop in neutral it drops from half a tank to dead empty. The first time it happened last night it freaked me right out--I thought for sure I'd look back and see my fuel tank rolling down the road behind me!

Yes, the fuel rushing to the front of the tank will have the sending unit nearer to the rear to have a lower reading.

I was half looking at the hybrid Escapes though...



If you get another daily driver, get a manual transmission so you throw it into neutral easier. Of course, you'll end up with a lot more wear and tear on your entire clutch system.

I'm not sure how it works with a automatic trans. but with a manual going downhill using the engine as a break: No gas is used 'cos the engin is turning anyway (over idle RPM). In neutral it needs some gas to idle, thus consumes more...
This apply to most injection engins with electronic control so I suppose it apply to ours too.

Any comments? Am I totally wrong?
/Freddy

While a manul transmission for this is the best option, an automatic tranny is also used for engine braking when its in gear, both when the TCC cluch is connected or even when it is disconnected (you still have fluid coupling within the convertor). You won't save gas at all, if anything you might use a little.

The problems with this shifting into neutral idea are that there are risks.

1) Lets say if you were stopping, threw it into neutral, and all of a sudden, you nedded to avoid a possible accident, by the time you threw it back into drive, (assuming you didn't react adversly and by mistake threw it into reverse), by the time you put it back into gear, and by the time the transmission actually engaged after you put it into gear, you could be to late and in an accident.

2) As stated above, its very easy to go a step further and knock it into reverse, there goes a good tranmission.

3) If you did this for stop and go, over and over, or if you used this method of braking down hills for a long time, you could easily overheat your brakes(because of a lack of engine braking), wipe your brakes out and bingo, no brakes. Thats the reason gearing down long hills with a load is safer and keeps you more in control by controlling speed thereby not using your brakes constantly.

4)Basicly just wearing out things like brake parts and stuff much faster. the possibility of damaging your transmission, etc., etc.

All in all, this will not save you any gas, and might make driving a little more dangerous.

^^ I agree.

Not to mention that coasting in neutral is illegal in most states....


316.2024 Coasting prohibited.--The driver of any motor vehicle, when traveling upon a downgrade, shall not coast with the gears or transmission of such vehicle in neutral or the clutch disengaged. A violation of this section is a noncriminal traffic infraction, punishable as a moving violation as provided in chapter 318.

^^ I agree.

Not to mention that coasting in neutral is illegal in most states....


316.2024 Coasting prohibited.--The driver of any motor vehicle, when traveling upon a downgrade, shall not coast with the gears or transmission of such vehicle in neutral or the clutch disengaged. A violation of this section is a noncriminal traffic infraction, punishable as a moving violation as provided in chapter 318.

I wonder why and if they could prove it during a collision.

I wonder why and if they could prove it during a collision.


Actually they can obtain the information if needed, if that was what was in question in an accident investigation. While I dont agree with it in general, as it, in my opinion, infringes on privacy laws. The newer ('98 and on for these trucks) can now access vehicle drivng parameters through a vehicle module, that records speed, gear position, whether the person was applying brakes etc etc. The information can be obtained.

i believe from 97 on up vehicles (at least gm) have "black boxes" that record vehicle data that can be retrieved to find the cause of a crash, just like an air craft.

Thanks guys, just a curiosity.

That is crazy how they can do that.

Guess it keeps us honest.

i believe from 97 on up vehicles (at least gm) have "black boxes" that record vehicle data that can be retrieved to find the cause of a crash, just like an air craft.

GM started using systems like this back in '95 and even ( I have to verify) I think in the '94 Oldsmobile Cutlass, so even back to starting in '94. I know for sure in '95 in some cars such as the monte carlo, the chev lumina, for example.

This system is a part of the air bag system, especailly vehicles with dual air bags. So basically if you had driver and passenger air bags, you could very well have this black box module, so to speak.

Even further, new GM vehicles that have OnStar, can gain this information without even touching your car, so to speak. A little food for thought, talk about big brother.

i didn't know it went back to 95. i remember seein something on crashes on tv and they showed this box thats in vehicles. but yea, kinda creepy but i guess its helpful, just as long as a stalker can't hack onstar and follow ur car around.

In my Olds Bravada I have a little information center in the upper console, one of the options is a "current MPG" reading...

When going down any kind of decent slope or hill when my foot is completely off the gas my current MPG quite often goes all the way up to 99mpg (which I think is as high as the digits can display).

So I would say it would be pretty hard to conserve any more fuel by shifting into neautral than you already are by gravity pulling your car instead of your engine pulling your car.




Now if I could jsut figure out how to make it ALWAYS display 99mpg I'd be in great shape!

Now if I could jsut figure out how to make it ALWAYS display 99mpg I'd be in great shape!

A little masking tape and a marker might work.:rofl:

^^ I agree.

Not to mention that coasting in neutral is illegal in most states....


316.2024 Coasting prohibited.--The driver of any motor vehicle, when traveling upon a downgrade, shall not coast with the gears or transmission of such vehicle in neutral or the clutch disengaged. A violation of this section is a noncriminal traffic infraction, punishable as a moving violation as provided in chapter 318.

Well, looks like this half baked idea isn't only a bad one, but illegal! Thanks for all the replies.

id love to see a cop try to pull me over for being in neutral. just think what the judges face would look like when u showed up in court with a ticket that says " drivin in neutral"

i know for a fact that most cars auto trannies have some sort of mechanism that prevents it from going into reverse if you are going foraward over a certain speed. i know that my blazer has it, as i have done that exact thing (shifting into neut for a downgrade, and accidently going into revers, nothing happened i just kept rolling).

black boxes can be ether your best freind or your worst enemy. one of the main reasons they are in cars is so that auto makers can use them against you if your car ever fails and causes a wreck and you sue them. they wil use it to show you were driving too fast (even if its just a few miles over) and thus the wreck was your fault. also, im sure insurence companies had soemthing to do with it too, cause they can use them to prove fault in an accident and cut out huge costs of crash investigations and litigation. you cant litigate against a computer log. but heres how they are good: supose you are in a wreck and it WASTNT your fault, you can use the black box to prove it. also, supose a cop writes you a bogus speeding (or other) ticket, you can use the black box to prove him wrong.

when my dad bought a '04 zo6 the black box worried us, we were afraid that if any of use ever had a horrific wreck the cops would yank the black box to see how fast we were going. "ah so you were going 160 when you flipped 5 times into oncomming trafic, looks like you get a wreckless driving ticket!" wreckles driving is punishable by 5 points, at least a 500 dollar fine, and even possible jail time. wreckless driving is driving 35 over or more, or just driving with total disregaurd to the safty of the people aroudn you. i looked up the laws regaurding these black boxes, and if tampering with them is legal or not (turing them off, turning them on, changin the loggs, pulling them out completly) and i found out the laws vary wildly from state to state.

in some states its illegal to turn them off or mess with them at all, in some states its legal to do whateve you want with them. in some states its actualy illegal for anyone but you to look at the logs even if you are in a wreck (aside from a warent). what i wanted to do was rig up something into the comp that would let me turn the logger on when i was just cruising around, but would let me turn it off for when i wanted to get buck wild. i gave up on it cause its exreemly rare for anyone investigating a crsh to actualy read the logs, they can tell how fast you were going pretty acuratly just from how you crash. also, unles your state specificaly says that its illegal to mess with your black box, you can just yank it out of your wreck pile and burn it.

One more thing these little black box's do for you is it tell's them if you and your passengers are properly seat belted in, I belive it records the last 60-90 min of your vehicle driving habit's... Happy Motoring......

I'm not sure how it works with a automatic trans. but with a manual going downhill using the engine as a break: No gas is used 'cos the engin is turning anyway (over idle RPM). In neutral it needs some gas to idle, thus consumes more...
This apply to most injection engins with electronic control so I suppose it apply to ours too.

Any comments? Am I totally wrong?
/Freddy

No, you are NOT totally wrong. As a matter of fact, you are probably exactly right.

If GM Powertrain engineers could devise a method of saving fuel on downgarades, they would. Every 1/100th MPG adds to their CAFE numbers, and helps keep the government off thie backs. I'm thinking they've already got it about right, otherwise a 505HP C6 wouldn't be able to make almost 30 MPG.

Nearly every GM ECM/PCM that I've hacked or custom programmed has factory parameters for DFCO (Deceleration Fuel Cut Off). This effecively cuts injector pulses to the engine (but keeps spark active) until a given vehicle has slowed to a given MPH. A lot of the older ECM cars used 11-12 MPH for DFCO. Moreover, while in neutral, the PCM has an idle RPM adder which increases the idle RPM when in PARK/NEUTRAL, thereby potentially using more fuel. So, throwing it in NEUTRAL is defeating the DFCO, increasing the idle RPM, and possibly damaging the transmission, although I'd really have to study the hydraulic schematics to see if that were truly the case. Coasting downhill in NEUTRAL could actually cost you mileage. If you're in OD, the forward sprag is likely freewheeling at coast anyway, so beyond the drag of the forward sprag (in an automatic) engine RPM should drop somewhat while running down a grade - It's pretty much already in a "neutral" condition.

I wonder what legislators would have to say about that. They're likely violating their OWN laws every time they drive down a hill, but they don't know it. No surprise, since most legislators don't know much of anything beyond PR and political science, which, in reality, is no science at all - It's more the art of being a self-important bull-shipper. There are a few exceptions, but they likely don't last long in government. Too bad for the rest of us.

i didn't know it went back to 95. i remember seein something on crashes on tv and they showed this box thats in vehicles. but yea, kinda creepy but i guess its helpful, just as long as a stalker can't hack onstar and follow ur car around.

That shouldn't worry you. If you use a celly, they already know exactly where you are within a 50-foot radius anyway. That's how most municipalities' 9-1-1 systems are devised, so that emergency help can be sent to the correct location even though the "phone" (really a radio) can roam all over. Any time you have signal (or a bar graph) showing connectivity to a cell tower, they've got you. If you travel between cells at too fast a rate, they know you've been speeding somewhere in there.

letting ff the gas or putting the car in neutral its like the same thing. you have main line pressure, throttle pressure, and governor pressure(new cars... the speed gear or reluctor wheel). throttle pressure comes from main line which can never be higher then main line, from the throttle pressure the fluid goes to the governor or what ever you may have. if you let off the gas there is no throttle pressure but there will be still some govornor pressure because of oyur speed. throttle pressure pushes on one side of a valve in your valvebody and the governor from the other . since there is no throttle pressure the llittle governor pressure there is engauges your shift valve. 1-2, 2-3, and your 3-4 (4l60e trans YOUR BLAZERS). so what im saying is that if your doing 40 mph down hill in drive your rpms drop because your actually in 4th gear. all automatics do that. so putting the truck in neutral then back into drive while your moving in any speed is just messing everything up, like the weakest link your sunshell. i just rebuild one cause the guy doesnt stop before going from drive to reverse and back, it just snapped right off the sunshell. not to mention that the 2-4 band is pretty thin and an be burned up real easy. ive seen it done on a dyno in 5 min. ive seen checkballs get blown through the seperator plate by high pressure engaugements