I've been trying to save gas lately for the fun of it and one of the things I've been doing is popping my automatic transmission into neutral for coasting long distances, because the rpm's go down a ton. Works great for me and never had a problem with doing so. What are your views on this?

DISCLAIMER: DO NOT even try it unless you know you're not going to even possibly bump reverse or park or anything... the way my car is laid out I don't have to worry about that.

 

Nothing wrong with doing that, you can indeed save fuel doing it. You might check and see if your Kia ECU has a feature called DFCO (deceleration fuel cut-off). If it does, merely lifting completely off of the gas while coasting in gear will actually use LESS gas than going to neutral. What DFCO does is completely shuts off the fuel injectors as long as there is enough momentum to keep the engine turning (usually above about 1200 rpm). When you're in neutral, you're using gas to keep the car idling.

I've never played with DFCO on an automatic. I suspect that forcing downshifts (gently) to keep the revs up will keep you in DFCO for a while.

Good luck!

 

Thanks for the info. I'm assuming my car doesn't have DFCO because when I looked up "DFCO kia" on google this was the first link to appear.

Thank god cars are smart... I somehow bumped reverse today(first time) and nothing bad happened.

 

I'm pretty sure almost any modern (2000+? maybe earlier than that) economy car uses DFCO, it's just something that most people didn't know about until the recent hypermiling trend.

You can tell really quickly with a ScanGauge or other OBD diagnostic tool. Fuel flow will drop to zero (among other things).

There are some sneaky ways you can check to see if you have it, though. Try accelerating up to a cruising speed in 2nd or 3rd gear (just because being in a lower gear will give you higher revs and more uninterrupted coast-down time) and then lift off the gas leaving the car in gear. Take note of the sound of the engine and the feel of the deceleration. Now, do the same thing again, but shortly after you begin your coast, turn off the ignition for a few seconds. If you have DFCO, no fuel was being burned, so nothing should change when you turn off the ignition.

Another way you might be able to tell is to hold the lowest gear your transmission allows you to select. Accelerate to maybe 20 mph, just enough to get the revs up. With the trans in low gear, it won't downshift, so you should feel smooth deceleration when you lift off the gas. With DFCO, you'll decelerate with no fuel (essentially, the engine shuts off) until the RPM gets to the point that it needs to sustain itself (somewhere around 1000-1200 rpm), then it will add fuel and the engine will "restart" itself to maintain its idle. You can feel a gentle surge when that happens.

If you find that you have DFCO, it's probably better to make use of that than shifting into neutral. Remember, shifting to neutral uses "some" fuel, DFCO uses "none". If you go down a looong hill (the kind we don't really have in FL), there may be benefit to using neutral to get a longer coast, but for our short coasts, especially "stoplight coasts" where you need to decelerate, anyway... you're better to use DFCO.

I'll warn you, though... just like the pursuit of speed, the pursuit of better gas mileage can become an obsession!

 

I got my car up to speed in second gear yesterday and killed the engine. The quick jerk it made kind of scared me, but surely enough when I turned the key a few seconds later it fired right up. And today I left it in gear and heard it downshift from 4th. So I guess it does have DFCO. I'll start using it so coast short distances and neutral when it's like a 1/2 mile. Thanks for the extra advice!

 

I'm not entirely sure you understood the process that I described, but I'm pretty sure you have DFCO, anyway. So... rock on.

 

I do get what you're saying. Coasting in drive uses no gas vs. in neutral it does use a little gas, because the engine is still receiving some fuel, vs. in drive where it's using the transmissions momentum to keep the engine turning and the fuel injectors are fully closed.

What I meant was that I figured it would still save more gas to coast a long distance in neutral(less wheel resistance) vs. in drive where it's being slowed down. However today I coasted a good distance to a long red light in drive, went from 45mph to 30mph vs. in neutral ending up around 35mph. So being in drive really doesn't slow it down as much as I thought. Good deal. Thanks again for the tip.

 

you also have a TON more in your transmission then a standard, so you have ALOT of extra momentum that generally in an auto doesn't slow you down as fast, but i'm weary of forced gear changes in an auto

 

Do you think a tdi has this feature? The jetta will coast forever, but our hills are alot bigger here.

 

The only reason I've heard that some vehicles might not have this is the need to keep the catalytic convertor hot. And it's quite possible that even on the cars that are known to have it that there may be a limit to how long it will stay in DFCO for that reason. (I've not really tested to see how long it will stay in it, as I'm either coasting to a stop, or doing "pulse and glide" and only coasting down 10 mph or so, neither of which takes enough time for the cat to cool down appreciably)

Should be even easier to tell if you have DFCO in a diesel, though, because you can really hear the diesel ignition at idle. If you lift off the gas and coast, does it sound like the engine is running? If you're not quite sure, turn off the ignition. If you're in DFCO and cut the ignition, nothing should change because the engine is already "not running".