OK so yesterday was the first official day of Spring and today it was an absolutely beautiful day outside, in the low 60s, "ceiling and visibility unlimited" as pilots sometimes say, so I decided to do something I very rarely do and "stretch the legs" of the FEH. Checked tires first, all OK.

First I opened up the sunroof shade and turned off the climate control completely. I also turned the radio off so I could be aware of any weird noises without distraction.

Then I drove the car on a nice, safe piece of highway with just some very moderate curves and modest hills up to an indicated 100 MPH and held it there with cruise control for almost 10 minutes, ticking off the miles with the dashboard clock and the mile markers on the side of the road to verify. At that speed the ICE turns just shy of 3500 RPM indicated on the tachometer. It was very smooth at 100 MPH with no vibration or control problems, no severe wind buffeting or anything like that. Yes, it was perfect weather and a nice day with almost no traffic. I wouldn't do it in any other circumstance. Bottom line: the FEH will pull 100MPH and maintain that speed without drama. That's the fastest I've ever driven it.

Then I decided to run at 80MPH in cruise control over the next 10 miles of mostly flat, perfect highway. Reset the MPG in the SYNC/NAV and: 34.1 MPG was the result!

That's awesome in my book. 80MPH in cruise and better than EPA by more than 10%. The ICE engine at that speed dropped to about 2400-2500 RPM and it just held there perfectly while achieving really good mileage. I was surprised because of the frontal area of the the car, I expected it to be a lot worse, but it wasn't. This was perfectly smooth highway, though, almost totally flat, and perfect weather and temperature. Optimum conditions, in other words.

Pretty good, I was hangin' with a new Mercedes SUV right next to me in my 11 year old Ford, and it was nice to see these results on a beautiful Spring day. Usually when I put it in cruise at 70 I see approx. 2000-2100 RPM on the tachometer if the road is flat. I think the tach. is a good way to gauge how well the Hybrid is optimizing power demand vs. speed through the eCVT. If all else stayed equal and the drivetrain developed about 1500 horsepower, this would be a 210+ mile per hour SUV. Don't try it. I'm satisfied with the 100 MPH and the good mileage having gone through the cold winter. Happy Spring!

 

I have found my 2008 FEH gets the best fuel economy at speeds over 75 mph. Around town at 40-60 mph I do well to star over 26 mpg.
This mystifies me.

 

That makes two of us. I was not watching the energy display at 100 or 80MPH, both hands on the wheel and eyes straight ahead, but the RPM hovered right around 3500 / 2500 respectively. 100MPH is pushing it to be sure, but it felt like it could do 80MPH all day long and I was mystified to see the final readout.

The torque peak isn't until 4500 RPM, where it maxes out at 136 ft./lbs, so it's not straining at 80MPH, the computer isn't commanding more power from the engine. It must be that the Atkinson-cycle I4 and the hybrid powertrain are in a kind of efficiency sweet spot at that speed. At least, when they're cruising in a straight line at a constant speed. Really pretty amazing when you consider the aerodynamics. This isn't a "slick" car. But Atkinson-cycle engines can be about 10% more efficient than standard Otto-cycle engines.

A little while back, I was watching John Kelly (Weber Auto on YouTube) tear into a Honda hybrid transaxle of one kind or another, and I thought I heard him say that the internal combustion engine running all by itself in that car was actually more efficient over 60 or 70 MPH than the series hybrid mode with the attendant energy conversions, e.g.: Gas engine --> Motor Generator --> Inverter ---> Battery and then back out Battery ---> Inverter ---> Traction motor.

It would be interesting to see the internal documents on this powertrain. I'm sure the engineers have a graph somewhere showing the peak efficiencies in various modes and where they are achieved. I don't think Ford was ever going to go out and say: "It's good around town, but really, y'all, just drive it at 75-80 for the best mileage."

 

Usually mileage tops out at about 80 km per hour since wind resistance rises very quickly after that. I don't think Hippos are any different unless in EV mode only or going downhill.

 

I have found that the Avg Econ reading on the dash isn’t very accurate after resetting and driving only a short distance. On my 2007 AWD, it tends to read overly-optimistic fuel economy if I reset it after the engine warms up, regardless of the driving conditions unless it’s uphill then it's horrible. Over the next few hundred miles it gradually levels off to something more typical.

As an experiment last week I reset the Avg Econ meter at the start of a 100 mile driving day and it read in the mid-30’s all that day, then we went on a camping trip the following weekend with about 200 miles of freeway and some logging road driving and it dropped to about 30MPG. On the way home we collected some rocks in the mountains to bring home for a landscaping project (elevation drop of about 2300’), and the economy climbed up to about 32MPG (haha, there’s another way to improve fuel economy). This is in contrast to the 27MPG it was reading prior to the reset. Next time I fill up the tank I’ll have to do a manual MPG calculation to see how it compares.

It seems like it may be useful to reset the Avg Econ periodically when the seasons change, but I wouldn’t trust it for short-range experiments. Would be nice to know how the average is actually calculated.

 

I agree in general that longer sample distances/times should lead to more accurate results. This was through the "Information" screen of the SYNC/NAV system, which seems to work pretty well. But it was only a 17 mile trip (I say 10 miles above but it was the return leg of the 100 MPH ten minute trip, approx. 17 miles) so I take the MPG reading with a grain of salt. It seems to track the instant MPG fairly accurately, but who knows what algorithms it uses to display the average? Is it calculating actual fuel flow through the injectors or is it "ballparking" it based on other factors? In other words, there are lots of ways to approximate fuel flow and MPG with this system, and we don't know what it's actually using.

It's interesting because the Information screen draws some pretty cool graphics during operation. For example, it continuously varies the widths of the little green marching ants that indicate the magnitude of energy being transferred between the ICE, electric motor, HV battery and front wheels, so presumably those little marching ants grow and shrink according to a numerical value coming from somewhere. But they do not display the values themselves for the various pieces, and just give you the instant and average MPG. I hadn't noticed the graphics changing in width until relatively recently, they're green on white and you have to watch closely, but they do.

It's in the code somewhere, but it ain't Open Source and not available for us to inspect.

 

Aha, my 2007 FEH has no SYNC/NAV system, just the LCD matrix under the Tachometer with Avg Econ and Instant Econ readouts (among other things) that you can cycle through with the INFO button. In place of the SYNC/NAV screen I have a fairly-nice aftermarket stereo, which frankly I prefer over an outdated navigation system. The stereo was there when we bought the vehicle last year; I don’t know if the SYNC/NAV system was removed or just not included in this model. The graphical fuel economy info might be nice though.

I find the instant econ readout on the LCD pretty useless, it’s basically just telling you how much you are pressing down on the accelerator pedal and doesn’t give any real data. Avg Econ is pretty interesting and that’s were I usually leave the LCD display at. Except when it gets preempted with SERVICE SOON message (the topic of my other thread)...

 

The ScanGage avg fuel economy may be more accurate. I'll try that.