coasting
 

i don't do it much , but i occasionally put the trans in neutral and coast down some hills....it does make a difference because even though i not giving it any gas , it revs more rpms when in gear...i'm sure the computer must be sending some gas......today i made what i thought was a really big and stupid move , i put it in reverse instead of neutral :eek::eek::eek:......i guess the hrr has a switch that kills the engine , for idiots like me :roll:.....i pulled over and stopped expecting to find that i had damaged somthing....nope , as far as i can tell , nothing....all i can say is thanks to gm.:thumb:

good to know that is built in, ha.

i coast down a big hill on my way to work every single day, unless i am behind some slow person and i gotta ride the brakes. The hill is large and about a mile long, and as soon as i pop it into N, the instamatic mpg shoots up and i ride at 99 the whole way down. I sometimes forget when i get to the bottom though, and go to turn the corner and hit the gas and all i do is rev it...

On my trip to Colorado, the best mileage I got was going up and down the Rocky Mountains. I guess downhill helps a lot more than uphill hurts. I got 5 mph better there than on flat road.

yeah i can see that. In my town it kills the mileage anyways. However the same hill in my last post, i can coast down it getting 80+ mpg, and when i go up it home each day i get between 18-24, usually around 22-23, not bad at all.

Guys, there's a feature built into the ECM calibration called DFCO (Decelleration Fuel Cut Off). Under many conditions when off throttle, the fuel will be cut off to the injectors completely (= NO fuel).

If you just put into neutral, basically you're in an "idle" condition, where there is some (not much, though) fuel being injected.

IOW, it won't make a big difference, but you're more likely to save gas by just leaving it in gear.

better?
 

i would think it would be better to have some fuel going into any engine while it is rotating....that is only my opinion....thanks for that info....due to that i may be coasting a little more in neutral , but i can't do it much because the terrain won't allow......also i don't understand how my mpg increases when put into neutral (according to the dash thingy) , unless it is causing mechanical "drag".

Catdaddy,
Is that on an auto trans?
Just an FYI if an auto trans ... When putting it in neutral, you only need to bump the shifter - not squeeze the trigger. It shouldn't go past neutral this way. You can just bump it back and forth between drive and neutral this way.

Joe,
Is that on the Auto or Manual? I would think that something like that would be on the manual trans. With a manual trans there is a mechanical connection between the engine and trans. If you didn't have fuel going to the engine in an auto trans, wouldn't the engine just stop? (I may be wrong on this... there may be enough residual friction to keep the engine turning at speed?)

[QUOTE=GCarp;399180]Catdaddy,
Is that on an auto trans?
yep , auto...thanks for that....so , what about the 2 other gears ? will go down past D without the lever thingy?....is this info in my owners manual ?...i've heard of a few having issues with the auto shifter , so i've always tryed to be gentle but firm with mine....i really can't believe i put it in R , but i did.:red:...i get a little tired/stressed on my 275 mile a day route.

mine is an auto as well, i never touch the button in, just a slight nudge between N and D. I've never tried to nudge past D since i've never really used the other 2 and would want to know what the I is for more before i did it.

in D i definitely think there is a mechanical drag. As soon as i switch over the mpg shoots up. Even if it didn't though, with Less resistance I can roll a lot farther. I have to watch the speed on mine since it is technically 25 or 35 (who knows...)

I've had my scanguage show no fuel to engine (0 l/100k) in I gear on a long downhill last week. So fuel cutoff is for real; this was on my automatic. It's done it another time in D while I was coasting behind slow traffic.

The engine keeps turning and it's not any different than normal behavior on deceleration; in fact I couldn't tell if I was not seeing the scanguage reading.

What's the harm? The engine is still getting lubrication, and it's the transmission that is turning the engine, but other than a bit of an extra load on the transmission, I don't see what could go wrong.

Yves

it probably does no harm.....but i see it like people using a manual trans to slow down instead of brakes......brakes are cheaper and easier to fix than trannies....and gas is not free.;)....i will consider that it may even be benificial to the rings and cylinder walls since there is no pressure pushing the piston it may be cleaning those parts , but i doubt it.....have you ever tryed to turn an engine by hand ?....either way i would surely think that less rpms on the engine means less fricton and wear....so my next ? would be about rpms and cooling.....less the rpms = less the cooling needed , unless the engine is stopped completely and no coolant would then be circulating....so now me think -coasting good if engine is still turning low rpms , and reverse lockout is working:thumb:

[QUOTE=catdaddy137;399184....so , what about the 2 other gears ? will go down past D without the lever thingy?....is this info in my owners manual ?...i've heard of a few having issues with the auto shifter , so i've always tryed to be gentle but firm with mine....i really can't believe i put it in R , but i did.:red:...i get a little tired/stressed on my 275 mile a day route.[/QUOTE]

No it won't go past D. It should only bump between N & D without touching the button (lever thingy;)). I don't think its in the manual.

The I is for Intermediate. Kinda like the old 2 on the shifter. I changes the shift points. IIRC they go to 3500 RPM from 2500 RPM and you lose the OD. Definitely higher performance in I.

The MPG does get better if you coast. Even though there is now fuel going to the engine as opposed to the cutoff on decel, you are not linked to the drivetrain and the car will roll farther in neutral than it will in D. I know I get better mileage when I do it.

I have a 5 speed manual transmission. today at speeds of about 30-45 I shifted into to 5th going down hills or on long straights on level ground. My mileage average went up .5 mpg in 20 miles with 250 total miles on the average. So I think if it went up that much in that short of time that it was really helping the mileage. I will continue this test and reset the meter and we'll see how it goes. JC

Just to let you know in most states it is illegial to coast in neutral.

Something to do with being in control of your vehicle...:roll:

how would any officer know you are coasting in neutral?

That, I can't tell you.......... :lol: But I guess if you got in an accident, it may come up.

Roller Coaster (of love)
 

I used to coast all the time with my old shifter (Nissan 5-speed). No coasting now with my Auto trans HHR. An automatic tranny seems to coast more anyway (in gear or not).

If you are actively shifting from D to N and back again, aren't you controlling the vehicle - even when it is in neutral? :confused: :D

I think it's allowed in coastal states on coastal highways.

:lol:

How are they going to know? Maybe a prism on a stick to see where your shifter is selected....

Most cars can shift between nutral and drive without touching the button, it's been this way for 20 years.

I remember seeing something in the "tech" section of Road & Track a while back on this subject. They asked some manufacturers to answer a reader's question about shifting into neutral to save gas while coasting. If I recall correctly, they indicated that it wasn't a good idea, either moving or stopped. In a manual transmission car, the point was made that you may get into an emergency where you'd need the power/control and not have it while fumbling to get back in gear. In an automatic it was noted that the wear you'd put on the transmission/shift linkage would be much more costly than the gas you would save, if you'd get any gas mileage advantage at all. I am guessing that the internal parts have to rev-match when you get through coasting and drop back in gear. I also recall discussion of how certain cars actually rev higher in neutral than in gear with your foot off, so any gas mileage improvement may be an illusion. I am no expert at this, but someone may want to ask GM their take on it. God Bless, Marc