Like many of you, I coast down hills whenever possible. You might have noticed that the car will occasionally shift down one or more gears while coasting downhill. This increases the revs and slows the car. I found that by flicking the right paddle shifter once or twice, the car goes into a higher gear, revs drop, and speed increases.

Of course, you don't want to be flying down a twisty hill at 90 MPH, but gaining a few MPH can help MPG.

 

Yup, coasting is extremely beneficial. You just want to make sure you don't upshift too early whereby it drops the revs to the point where you are not in DFCO mode anymore. Or you can shift to neutral (when at slower speeds) for longer coasts.

 

DFCO mode? Shifting into neutral doesn't appeal to me, although I used to do that with manual shift cars. Going to work, I could shut off the engine one mile from work and coast into my parking space. It's nice living in the country.

EDIT: DCFO - got it. That must happen when the current MPG goes over to 90.

 

Yup, in DFCO your MPGs are actually infinity since you're using no fuel and your bar graph will be maxed out. In most vehicles with DFCO, the injectors will fire back up right around 1000 rpm.

 

DFCO = engine braking. No, you're not burning any gas at the moment, but ∞ isn't exactly the way I'd phrase it.

It is the most fuel efficient way to slow down a bit, though.

 

Since the engine is running,. it must be burning some fuel.

 

The wheels are turning the transmission, which in turn spins the crankshaft moving the pistons, cams, valves, etc, but the fuel injectors are not spewing any gas, so in effect, the engine is "running" without being fed any fuel.

 

The engine is spinning, but it's not "running" in the sense that no fuel is being burned to spin it. Deceleration Fuel Cut-Off is when the computers figure out that you're beyond not having any load on the engine: the car's momentum turning the wheels is the source of power that is spinning the engine so fuel is cut off because it's not needed at the moment. The electrical systems stay up and so do any pulley driven accessories because they don't care what's making the engine spin as long as it's spinning.

The drag from pumping and friction act as a brake. Engine... braking. So while it does cut down on fuel usage, if you weren't otherwise going to slow down- like on a hill, with traffic or a stop, then it's a bad move for fuel economy because it's braking.

 

Wait, I just re-read your post, you were able to EOC (Engine Off Coast) for 1 mile? Incredible! That'll really raise your average mpg..............so jealous.

 

Very nice Charlie, a new record tank huh?

 

I had a bit of an odd week, with some errands that let me stay off the big highway.

 

You'll have to adjust your mpg figure for your longest tank in your sig, otherwise you'll be undervaluing your hypermiling skills.

 

I wonder if there is any longterm drawback to shifting into neutral going down hills.

 

There is. It means you're missing out on lots of EOC!

GoBucky- Oops. Thanks for catching that.

 

I hope not, I've been doing it for years on several cars.

 

I've done it with manual shift and also automatic, but never with a CVT. Depending on when I shift into D, I may have to rev the engine a bit.

 

Hmmm...

Pumping losses and engine friction exist during fuel injection also, so I am not sure you are correct. What is the position of the air throttle during DCFO ?

 

I don't have a lot of driving time in my wife's AT Fit, but I think I have found a pretty sweet spot of over 50 MPG when driving on level roads and keeping RPM below 1800 RPM. This works out to speeds in the 50s MPH.

What does this have to do with your post, you ask ? Driving with load* (DWL) on hills gives me the same 50+ MPG so long as the traffic can tolerate the speed changes going up and down hills.

*DWL means you keep the fuel throttle steady.

 

Right. Going uphill with a steady throttle makes a considerable difference, depending on the traffic. With cars behind me, I can't just let the speed drop.

 

Yes, this is true, but engine friction (i.e. engine braking) is much more significant in DFCO as opposed to engine braking when the injectors are firing.