MPG vs MPGe vs MPGc

[bz101]

I am new to the Fusion Energi (~1,000 miles) and have a question on calculating MPG and what the Energi actually calculates when it says "Average MPG".

 

I did read a few posts here and out on the web about the difference between all 3.  I want to confirm my understanding:

 

1) MPG = traditional gas-powered calculation that does not take into account electric mileage or cost

2) MPGe = (gas and electric mileage) divided by gallons of gas used (doesn't take into account the cost of electric)

3) MPGc = (gas and electric mileage) divided by (cost of gas + cost of electric)

 

Is that right?  So MPGe is misleading if you're trying to figure out how much money you're really saving because you can't just take the old MPG and compare it to the new MPGe.

 

What is the "Average MPG" shown on the left-hand display in the Energi?  I assume it's MPGe.

 

Any thoughts on how to manage MPGc?

 

Thanks for your help.

[murphy]

Not quite.

 

http://en.wikipedia.org/wiki/Miles_per_gallon_gasoline_equivalent

[Kybuck]

2014s only report MPG on the display, and cannot be changed to MPGe (2013s could).  An all-electric trip is reported as "999" MPG.

 

If you drive 10 miles on pure electric, and 10 miles in hybrid mode at 40 MPG, the car would report that trip as 80 MPG (total number of miles divided by gallons used).

 

Although, My Ford Mobile still reports in MPGe - but even that isn't a pure MPGe calculation and overstates the efficiency in electric mode by not taking the charging inefficiencies into account.  This difference is bigger for Level 1 (120V) charging than for Level 2 (240V).

 

MPGc is not a real thing... MPG has never been a "cost" number, seeing as gas prices vary...  likewise, electricity prices also vary (region to region, and even at different times of the day depending on your plan).

[EnergiCCAATS]

So, I guess  our  electric  mode MPGe here in the southeast (where rates average about $0.07 per kWh) would actually be significantly higher than the sticker's posted 100 MPGe.

Edited May 25, 2014 at 12:24 AM by EnergiCCAATS

[Kybuck]

No, that isn't how MPGe works.

 

MPG is not a cost calculation.  It it purely the number of miles divided by the gallons of gasoline used.  Most people know and understand this general concept.

 

MPGe also is not a cost calculation.  The calculation is more in-depth and conceptual than a standard MPG calculation.  First, convert the electrical energy used into "equivalent gallons".  The "equivalent" units in this case is BTUs (a unit of energy).  A gallon of gasoline has 116,090 BTUs.  A KWH of electricity has 3,412 BTUs - therefore, one gallon of gasoline has equivalent  energy as 34.02 KWH.  So, MPGe is the total number of miles divided by gallons of gasoline + equivalent "gallons" of electricity.

[Cody Permann]

So I find keeping a cost-based number that can be expressed as some sort of "MPG" is useful when talking to people who are unfamiliar with PHEV vehicles. Telling someone that you get 120 MPG, or 60 MPGe is only moderately useful. The former is just an overblown figure that is often way off if you drive mostly on electric and the later might diminish the actual savings of driving a part-time electric vehicle if your electricity is cheap. Another alternative is to quote the cost per mile but most people don't have a good idea of what a typical number is or what their vehicle might get so that's not very useful either. I've been keeping a spreadsheet for my vehicle that tracks MPG, MPGe, and a cost-based MPG number to give people an idea of how much it costs me to drive.

 

Yes I realize that MPG has nothing to do with cost, but you can come up with cost based number if at a given fill-up you take the cost of your fuel + the cost of your electricity that you've consumed and figure the amount of fuel you could have purchased for that combined cost. You then divide that pseudo-gallons number by the number of miles you've driven to get an "MPGc" number that you can quote to friends. That number can and will change quite a bit depending on the costs of fuel and electricity in your area but I still find it useful. My electricity is very cheap and I always use 220V charger to further minimize charge losses so my MPGc is always higher than my MPGe number.

 

Bottom line: My FFE is about a third of the cost to operate as my previous vehicle. 

Edited December 22, 2014 at 06:37 PM by Cody Permann