On Thursday, July 20, 2017 at 7:02:18 PM UTC-4, Ed Pawlowski wrote:
On 7/20/2017 3:56 PM, trader_4 wrote:

The readout on the computer still says 25 even though you only get 23.
Sort of like saying if you had pure gas this is what you;d have gotten
but you got something else.

Not if it's doing MPG the rational way, which, like DPB said is
simply distance travelled and gallons injected. It's not
calculating BTUs injected, at least not from the description
given, nor is there any reason to factor in energy content,
since the car doesn't know what it is.


Seems GM is not rational. In any case, it is always optimistic in my
experience.

GM says this:

Roger Clark, senior manager of GM's energy center, explains that the
fuel economy gauge makes a calculation by counting the number and
duration of pulses made by the fuel injectors as they squirt gasoline
into the combustion chambers of the engine. The onboard computer system
divides the distance the car travels by this estimated fuel consumption.


I don't see how it could be any clearer that they are simply
computing based on volume of gas used and distance traveled.

The latter part, where they talk about the fact that the
energy content of the gas makes a difference in MPG doesn't
change the fact that it's calculated the way you'd expect.