Using DFCO to increase your MPG

[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.

[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

[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