Using DFCO to increase your MPG

[talnlnky]

seemed pretty magic to me, i instantly saw a 10% (4mpg) increase in mpg's after I started using it.

[sbergman27]

seemed pretty magic to me, i instantly saw a 10% (4mpg) increase in mpg's after I started using it.

You mean... after you started consciously aiming toward decelerating over a longer distance and using the brakes less?

Reality check: Consider that if you manage to stay in DFCO mode for a full hour, you've only saved about 0.2 gallons of fuel (specifically due to DFCO) since the Yaris' engine uses about 0.2 gal/hr at idle. To get a 10% improvement in fuel economy over the course of a tank of gas, you would have to spend over 5.5 extra *hours* in DFCO mode. Do you think that you are managing that much?

-Steve Bergman

[BailOut]

Originally Posted by sbergman27

You mean... after you started consciously aiming toward decelerating over a longer distance and using the brakes less?

Reality check: Consider that if you manage to stay in DFCO mode for a full hour, you've only saved about 0.2 gallons of fuel (specifically due to DFCO) since the Yaris' engine uses about 0.2 gal/hr at idle. To get a 10% improvement in fuel economy over the course of a tank of gas, you would have to spend over 5.5 *hours* in DFCO mode. Do you think that you are managing that much?

-Steve Bergman

You have quite the attitude about all of this, Steve. DFCO may have existed for a while but it is/was far from common knowledge. Just because you knew about it earlier doesn't turn the rest of us into bumbling idiots, or negate the uniqueness of me discovering and proving it on my own.

While what you say may be technically accurate you completely overlook the fact that fuel efficiency techniques bleed into and overlap each other. It is nigh impossible to extricate an intertwined technique from its siblings, so striving towards DFCO usage will invariably lead to more efficient usage of brakes and deceleration and downhill throttle control while simultaneously making the driver more FE-aware in general. If it is easier for folks to understand that whole set of skills simply as DFCO usage please let them be.

Please try to look beyond the trees so that you can see the forest. Getting caught up in the minutiae of an easy-to-understand and easy-to-use technique will do no one any good.

[Loren]

Valid point, Steve. We're probably seeing most of our gains in MPG simply from changing our driving habits. DFCO is a good excuse to do it, but we wouldn't be using THAT much more fuel if the engine were idling at all times.

Let's say I was driving conservatively and went 400 miles on 10 gallons of gas. (a reasonable assumption for me, I usually do much better than that in city driving) My average speed for this tank of city driving is 30 mph, so total driving time is 13.3 hours.

Let's say that instead of clutching in and letting the engine idle, I spend 20% of my driving time coasting in DFCO. How much of a difference is it making? 13.3 hours x 20% = 2.66 hours at .2 gph... call it .5 gallons.

400 miles / 10 gallons = 40 mpg
400 miles / 9.5 gallons = 42.1 mpg

Wait... 42.1/40 = 5.2% improvement!

So, yeah... the bulk of our improvements (easily 10-20% over EPA without trying hard) come from driving style changes. But, I'd say that there's a solid 3-5% or more to be gained from making good use of the DFCO feature in city driving. And for people who practice the "pulse and glide" technique, DFCO can improve their highway mpg, too.

No, it's not magic. No, it's not "new" technology. But, now that people know about it, they have developed repeatable driving techniques to take advantage of it.

Footnote: Is it possible to spend 2.6 hours of a tank of gas in DFCO? I think so. Using myself again: My typical trip is maybe 20 miles round trip. If I don't hit at least 20 stops on that trip, I'm stunned. So, for each of those stops, I'm doing a full 20 seconds or so of DFCO coasting. Call it 7 minutes for every 20 miles. 20 of those trips on a 400 mile tank gives us 2:20 just from traffic lights. That's not including the amount of pulse & glide that I do. I'd say for any given mile that I spend cruising at speed, I'm DFCO coasting at least 10 seconds. (if my cruising speed is 45, that's 10 seconds out of every minute and a half, not at all unreasonable) This might only apply to half the miles traveled (the rest of the miles are spent accelerating or decelerating due to stops), so there's 200 miles x 10 seconds each for another 30 minutes of DFCO. I think my estimates here are very conservative for when I'm seriously "hypermiling", and they've added up to 2:50 of DFCO time.

While I completely get what you're saying, Steve... you can't deny that DFCO absolutely CAN make a difference in fuel economy for the driver to takes complete advantage of it.

And it all goes hand in hand. If you're maximizing your DFCO time, you ARE driving conservatively.

[Loren]

Brian and I were typing at the same time... and said much the same thing in the end. Brian went on to say a few things that I was thinking, but didn't say because my post was too damned long already. Heh.

[sbergman27]

Originally Posted by BailOut

You have quite the attitude about all of this, Steve.

I believe in accuracy, and in correcting misleading and/or erroneous information. What you discovered is that brakes turn kinetic energy into waste heat and that conserving kinetic energy helps fuel economy. DFCO is a relatively minor enhancement to that.

My clarifications in no way reduce the value of the information you have provided. But having a more accurate grounding in *why* it works will allow people to make more effective use of it.

That's not "attitude". It's a simple respect for truth. I believe in calling a spade a spade.

-Steve

[sbergman27]

Originally Posted by Loren

Footnote: Is it possible to spend 2.6 hours of a tank of gas in DFCO?

Actually, that's not the right question. You must spend that amount of *extra* time, over and above what would have been the case had you never even heard of DFCO, in order for the changed driving technique to result in that much improved fuel economy. And modern DFCO is designed so that people *don't* need to know about it to benefit from it. (I think the RPM cutoff on the Yaris is 1100 rpm?)

As mentioned in my previous post, this is about people having an accurate understanding of what is going on. And appealing to the fact that efficient driving practice involves a lot of interacting factors is really irrelevant to that point. Because the benefit specifically attributed to conscious use of DFCO *can* be separated out, and is relatively small in the grand scheme of things.

That doesn't make DFCO bad or insignificant. It just defines its place in the landscape better.

-Steve

[talnlnky]

Originally Posted by sbergman27

You mean... after you started consciously aiming toward decelerating over a longer distance and using the brakes less?

Reality check: Consider that if you manage to stay in DFCO mode for a full hour, you've only saved about 0.2 gallons of fuel (specifically due to DFCO) since the Yaris' engine uses about 0.2 gal/hr at idle. To get a 10% improvement in fuel economy over the course of a tank of gas, you would have to spend over 5.5 extra *hours* in DFCO mode. Do you think that you are managing that much?

-Steve Bergman

no... had nothing to do with being more conscious... It had to do with coasting in neutral, vs in DFCO... that instantly bumped me up from 36's to 40's. I was trying to get good mpg's from the first day i bought my yaris... took a few months before i found out about dfco. When you are going down a nearly 2mile long stretch of 5% grade highway at 60-65mph, your engine is using more gas than at idle.... I was able to change that 2 minutes of gas in my commute every day into zero gas usage. Then you add in all the coasts on highway exits that are a quarter mile long, then all the coasts to a stop sign/stop light...etc.

It's easy to rack up time in DFCO if you were making sure you were coasting in neutral before you heard of DFCO.... The last stick car I had owned was a 86Jeep Cherokee I had in HS. It didn't have DFCO... so I always popped it into neutral when coasting.

[sbergman27]

Originally Posted by talnlnky

It's easy to rack up time in DFCO if you were making sure you were coasting in neutral before you heard of DFCO....

Another way to put that is that it is easy to rack up more time in DFCO if you drive the car the way normal people do instead of trying to be clever with hypermiling tricks like coasting in neutral. These systems are designed with normal people in mind. Thus, there are sometimes FE advantages to being normal.

Regarding relative fuel use between normal idle and 65 mph in neutral, the Yaris uses about 20% less fuel in neutral. Normal idle uses 0.20 GPH, whereas coasting neutral uses 0.16 GPH.

So in 2 minutes of DFCO, you are saving a whopping 0.0053 gal (1/187th gal) of gasoline compared to coasting in neutral. Which is about 1/2100th of a tank. Keeping in mind, of course, that it takes longer to get down the hill with the transmission in gear due to that fact that the engine braking slows you down. So the actual savings would be less than that.

-Steve

[BailOut]

I see that you live in Oklahoma, Steve. Please try to expand your horizon enough to realize that not everyone lives in the Great Plain. Many of us, talnlnky included, live in hilly and/or mountainous regions, and in these areas it is not uncommon at all to be in DFCO for extended periods of time.

During my own commute there are instances where I am in fuel cut for as much as 7 miles at a time, for a total of around 20 miles per workday. Considering that commuting represents 90% of each tank, calculate that and then tell me that DFCO doesn't mean anything to FE.

[talnlnky]

Originally Posted by BailOut

I see that you live in Oklahoma, Steve. Please try to expand your horizon enough to realize that not everyone lives in the Great Plain. Many of us, talnlnky included, live in hilly and/or mountainous regions, and in these areas it is not uncommon at all to be in DFCO for extended periods of time.

During my own commute there are instances where I am in fuel cut for as much as 7 miles at a time, for a total of around 20 miles per workday. Considering that commuting represents 90% of each tank, calculate that and then tell me that DFCO doesn't mean anything to FE.

Well, I used to live in a Hilly/mountainous area, now it's more of an extremely slow grade... but from time to time I get to go up and down some hills, or even the Cascade mountain range.

Some of my best tanks of gas have come from commutes that involved hills/mountains, where I was able to coast A LOT in gear.

[Yoda]

so DFCO is better than coasting in neutral? cause i get 27 mpg right now lol

[sbergman27]

Originally Posted by BailOut

I see that you live in Oklahoma, Steve. Please try to expand your horizon enough to realize that not everyone lives in the Great Plain.

Big mistake there, Bailout. My home address is in Oklahoma. But I drive to New Mexico, and/or Colorado nearly weekly. In fact, I just got back from Grand Teton National Park, in northwestern Wyoming, just south of Yellowstone, a few days ago.

(Yes, I drive *quite* a lot.)

Nice try. But you really need to get out more before you counsel me upon "expanding horizons". I probably cover more ground in a month or two than you do in a year. And more varied (and mountainous) ground, at that.

So why don't you try addressing the facts I've presented rather than trying to sneak in a personal attack based upon your guess about my driving experience. I have made quite a number of factual points, in previous posts, which you seem set upon ignoring.

Look. DFCO is a handy tool in the tool chest. But you have overemphasized it in comparison to some of the other useful tools there. I like seeing 9999 on my Scangauge II as much as anyone. But even over extended DFCO periods, the effect needs to be kept in perspective. Because the Yaris engine easily uses 20 times its idle consumption just as soon as you start ascending the next hill.

-Steve

[sbergman27]

Originally Posted by Yoda

so DFCO is better than coasting in neutral? cause i get 27 mpg right now lol

Probably a little. You save about 0.00004 gallons for each second you do it. But you incur a fair amount of engine braking. And any fuel that did go through the engine if DFCO were not active would go to propelling the car forward.

So it really depends. Judiciously applied, it can help. But the ECU software is designed to do best when you don't try to second guess it.

[BailOut]

Originally Posted by sbergman27

So why don't you try addressing the facts I've presented

Because your "facts" change nothing. At the end of the day everything that you've presented is interesting but completely unnecessary, and contains as much opinion as fact.

I say again, getting caught up in the minutiae helps no one. Let us agree to disagree on the best implementation and/or public understanding of DFCO and move on.

[sbergman27]

Originally Posted by BailOut

Because your "facts" change nothing.

Tell you what. Using 0.16 GPH for coasting in neutral, 0.20 GPH for idle, and 0.0 GPH for DFCO, and ignoring engine braking factors for now... why don't you work out for yourself how much DFCO could realistically be saving you on a per tank basis? I don't really care about the answer. But I think it would benefit you to go through the exercise.

Sorry if you feel I stepped on you toes regarding your "discovery". But the numbers I have presented cut to the very heart of this matter. If you disagree, then please present an alternative model.

[why?]

wow dude you're just being a jerk. This is the real world, not some lab.

[skoolafish]

awesome. i did not know this