Eco-cruise mpg "sweet-spot" or Instant MPG calculation glitch?

[kostby]

Based solely on the Instant MPG display 'gauge' on the dashboard, our C-MAX apparently gets significantly better fuel mileage at 66-68 mph  -roughly 47 mpg- than anything between 55mph and 65 mph, or speed higher than 68 mph.

(Like an indicated 35mpg on the same stretch of road when traveling between 55 and 65mph, and above 68 mph.)

Today I managed to capture a photo of it in action.

 

 

I began noticing this a couple of days ago when we made our first of several daily trips this week down the same stretch of Interstate at about the same time of day.

 

On the 7-mile same stretch of level northwest to southeast interstate highway, traveling in either direction (thus minimizing any minor change elevation and effect of prevailing wind out of the west), our 2013 C-MAX SE with 3 passengers and no luggage aboard, our car displays an instant mpg well over 40. I estimate it at about 47. While there was light traffic, none of it was within 200 feet, so any effect of 'drafting' was minimal.

 

Other data:

The car is traveling at a steady 67.5 (indicated) miles per hour in Eco-cruise, and has been for at least 2 miles at the point where I snapped this photo.

The ICE is providing all the power. 

HVB is not discharging. (I just noticed that the attached photo above managed to catch it while neither charging or discharging. Here's .2 miles earlier when the HVB was charging: )

Location: Interstate 65, between mile markers 130 and 137, northwest of Indianapolis, IN.

Time 10-11 a.m. EDT

Tires inflated to 44 lbs.

AC off, temp set at 68 degrees, cabin fan set on '2'. 

Ambient air temp of 65-70 degrees

ICE fully warmed up by driving at least 8 miles, 4 in town, then 4 at highway speed.

 

Returning home on the same stretch of road, the display was a bit lower, about 41-42 (slightly into the prevailing westerly winds).

 

So, what have I just discovered?

1) an eco-cruise sweet spot

2) a glitch in the formula used to calculate and display instantaneous mpg

3) a point where the fuel delivery system is flat-out lying to the computer about the actual rate of fuel consumption

4) the EXACT location and speed where Ford tested the C-MAX and achieved 47/47/47 EPA numbers

5) a Twilight-Zone-sized hole in the space-time-fuel-consumption-continuum where the normal rules of physics don't apply (doooo-do-dooo-do-doooo-do-dooo-do…)

Edited August 15, 2014 by kostby

[fotomoto]

Jus-A-Cmax discovered this a good while back.  The quick synopsis: build up to a little more than 3/4's full battery at highway speed, select eco-cruise at 70mph and then reduce it to the 66-68mph zone without letting it drop into EV mode.  The last part is sometimes easier said than done.    

Edited August 15, 2014 by fotomoto

[Adrian_L]

Intriguing....

 

From what I remember, the "sweet spot" for a gasoline car was determined to be around 35-55 mph.   It boils down to engine efficiency compared to drag, friction, etc.  It's somewhat counter-intuitive but when you go slower than 35 you can't drive in top gear and the engine is less efficient.

 

Electric cars are another matter.  The sweet spot is 15-20 mph.  How hybrids or the C-max fits into this I'm not sure, but given the weight of the C-max I'm inclined to be skeptical of the 68 mph sweet spot.   

[C-MaxSea]

Huge thread here under 'Tips & T _______s"

http://fordcmaxhybridforum.com/topic/1434-i-have-found-the-illusive-mpg-sweet-spot/

 

We enjoy the 'secret sauce' when the car slides into it in ECO cruise, but rarely, because there is almost nothing flat here.  We seem to do just as well or better allowing the car to select going from EV to ICE and back again (all in ECO cruise) on the freeway at 65-68 mph - 46,47,48,49 MPGs (trip gauge), March to November  ;).

Nick

Edited August 16, 2014 by C-MaxSea

[kostby]

I can see how I missed that whole discussion about high ICE mode - last post there was in December 2013, and I didn't start reading until January 2014.

Today, I looked in this, the 'Fuel Mileage' section and didn't turn up anything. Never looked in 'Hybrid Tips & Tricks'.

[SnowStorm]

First, IMNSHO, the instantaneous gauge is nearly worthless.  Its usually bouncing between 20 (charging merrily away and getting people depressed) and 60 ( ;) ) in EV where it should be "infinite".  The only useful reading is the "high ice" mode where the battery is "fully" charged (about 85% indicated), stable and you are on a dead flat road with no other variation in load.  Any other time its just a meaningless curiosity.  I have seen it settle down at about 52 mpg when going 55 mph.  There is no way you get 35 mpg at 55 mph.  You may be going in and out of EV.  The slightest, and I mean slightest, change in slope will kick you in or out of EV at 55 mph.  One short blip of EV and it takes "forever" to get things settled again.

 

Second, I still think you can get better mileage with slight rolling hills that constantly flip you in and out of EV while ECO cruising.  Your mileage may be as good at 60 or 65 with rolling hills as on dead flat at 55.

 

Third, I doubt there is anything crazy about the gauge programming or fuel measurement (except that its always a bit optimistic).  My 2C.

[Jus-A-CMax]

kostby - there are a lot of "Area51" stuff on this forum...u jus gotta find it. After all, no one is going to hand you golden nuggets....

 

Now, I really miss the Ice High MPG, it was really a nice feature which has since - imho - been lost with eV now to 82mph. I don't care that others may say its still alive if you bleep the pedal but I have never got it the running MPGs as high and I know how to charge to an almost full SOC and feather the pedal.

[drdiesel1]

You're getting battery/ev assist and that won't last long ;)

[C-MaxSea]

Yup to Snowstorm, outside of 'High ICE', limited value from the instantaneous MPG read out - rather, for us it is just:  is it blue (EV) or white (ICE), how is my HVB charge, what is the road grade ahead (should I tap into the battery or push some extra ICE), and occasionally how am I doing as shown on the daily trip 2 gauge.  Sadly, there are too many clicks between Empower and Trip 2 - a big peeve of mine.   Net result for us is letting the car dictate driving mode in ECO cruise about 90% of the time on our hilly freeway (70% of our C-Maxing).  Nick

 

(PS  extra heavy duty peeve is that Trip 2 on My View will not show MPGs even though there is room for it - ARGH !!!!! That would be very handy to me.  My View has very little of value to us (other than temp gauge for mountain passes))

Edited August 17, 2014 by C-MaxSea

[ScubaDadMiami]

I found that 67.5 gets the 47 MPG on mine, too. In fact, you'll see that I find that the sweet spot for highway driving on long trips in this post.