MPG indicators and calculation

If the engine is running, the fuel consumed is increasing. But if the transmission is in Park, the miles run is not increasing. Simple math, the MPG since the meter was reset is decreasing.

 

Exactly. When M is constant, but G increases, (M/G) must decrease.

The fuel consumed while stationary is not free. It has to be counted too. Otherwise, non-hybrids that always waste fuel while idling, even when already warm, could exclude that wastage and claim higher MPGs.

 

But your Prius did get zero miles per gallon for that tank. No way around it. You put 11.9 gallons in, burned it and never moved. Zero MPG. On the plus side you probably got a heck of a lot of BTUs.

 

Just make sure if the ready light is on the car is moving. LOL

 

If you only counted MPG while the car was moving, most users would wonder why they were buying so much gas for a car that got such incredible mileage.

And once you start counting "only moving", why not go farther and only count "only moving fast"? Or "only moving efficiently"?

It'd be interesting if your philosophy applied to everything. Imagine me telling the electric company: "You can only count watt-hours spent while I was home. I mean, just because I leave all my lights on all day while I'm at work doesn't mean I should have to pay for light that I don't use."

Or how about refunds at restaurants for unused food/drink? "I only drank half of my glass of tea, so I want you to charge me half price. And I don't like carrots so I didn't eat them, and I figure that's 25% of my meal, so refund it to me."

My wife actually had a renter at one point who was going on a trip overseas for 3 weeks and so only wanted to pay 1/4 of her rent, since she wouldn't be there for 3/4 of the month. My wife said no. I'd have said, "Sure, as long as you don't mind your stuff sitting on the sidewalk for 3 weeks."

 

The gas was consumed, and it wasn't free.

Excluding that gas would reward bad warm-up behavior, encouraging lots of stationary fuel burn to get the engine up to ideal operating temperature. The resulting MPG displays would be fiction, with the 'best' mpg results produced by those wasting the most fuel. That is what would really be 'lame'.

 

I have the same question is their a life time average? Some people have reported it but I can not find it on the display.

 

Unfortunately, there is no honest way to separate driving efficiency from fuel burned while not moving. Engines must be warmed to and maintained at operating temperature to operate efficiently. Fuel burned while not moving is a very important contributor to that warming process.

Idle fuel burned while stopped at stop signs and traffic lights is a big factor in city economy. Excluding it would not change Prius' mpgs, but would significantly boost the claimed mpgs of non-hybrids.

Excluding non-moving fuel would lead to lots of MPG ratings cheating, with nearly all the benefit going to gas wasters. The Prius' efficiency rating advantage over non-hybrids would significantly shrink.

This is similar to the plug-in hybrid claims of '100+ mpg' without any mention of the electricity required to achieve that result. From my engineering viewpoint, the exclusion is a fraud.