Random thought reguarding ICE off/MPG figures

[Chris D.]

The second you turn off the ice, your not using ANY fuel,
so how can the miles you rack up dead coasting be counted as
"miles per gallon" if your engine isn't burning any fuel/gallons to run?

So all these 100mpg cars, dont really count theoretically because
their not burning the fuel, your just racking up the miles on the odo..

So if I were to keep the ignition on, ice off and just spun
my tires by hand for miles and miles, isn't that pretty much
the same thing reguardless of the vehicle being in motion?

Just a thought..

[basjoos]

It applies just as much as when you are sitting motionless with your engine idling for hours, where you are burning gallons, but have no miles to go with it, so how can that be counted as "miles per gallon". So theoretically you aren't getting 0 mpg, its just a figment of your imagination (and wallet). It'd be pretty much the same thing if you poured that fuel out on the road and ignited it.

An even more hair-splitting exercise is; if your odometer is broken, then you can't get anything other than 0 mpg, since instrumentally you haven travelled any distance.

Both scenarios, yours and mine, are at extreme opposite ends of the range of mpg figures your car can produce. What matters in the end is how many gallons you pump to fill your tank versus how many miles are on your odometer.

[MetroMPG]

Originally Posted by Chris D.

So all these 100mpg cars, dont really count theoretically because their not burning the fuel, your just racking up the miles on the odo..

Then you'd also better not count the hundreds of millions of vehicles (including yours) equipped with deceleration fuel cut-off, since they're also collectively racking up millions of miles when they're not using any fuel.

[bennelson]

Keep in mind that if you use your engine to get up to speed, and then turn off your engine and coast - you ARE still powering your car with your engine!

Your forward movement energy came from somewhere - the gasoline you already burned back a ways.

If the energy didn't come from the gasoline, what magical force is pushing you forwards?

Now if you did all your MPG calculations while pointing downhill - THAT would be cheating. The magical force there would be gravity.

[Lazarus]

Originally Posted by bennelson

Now if you did all your MPG calculations while pointing downhill - THAT would be cheating. The magical force there would be gravity.

I don't understand this whole thread but cheating what? It's miles per gallon (MPG). If you travel 400 miles on one gallon of gas your MPG would be 400. Who says anything about engine on/off it's just MPG whether you push the car the whole way or drive it you went 400 miles and only burned 1 gallon of gas.

[MetroMPG]

I think the point about how the car got to the top of the hill is valid. (I mean, if you get there on the back of a tow truck, or pushed it up with your friends, then the potential energy didn't come from your gasoline...)

I've heard a variation of this debate about hybrids. After all, some of them can drive on electric power for a mile or two, so should that count? Of course it should, since all the energy stored in a hybrid's battery ultimately came from burning gasoline. Except possibly for the very first charge when the battery left the production line.

I don't really think it's much of a debate.

[bennelson]

Plug-in Hybrids could then be debateable about gas economy.

In a hybrid, all the energy comes from the gas. In a plug-in hybrid, energy comes from both the wall outlet AND the gas.

Think we might need a spreadsheet to figure that one out.

[MetroMPG]

Definitely agree about plug-ins. Some of the numbers being thrown around right now are frankly deceptive because they don't count the energy from the wall.

[jcantara]

You have to look at averages, that's why. Yes, while you are engine-off coasting, you are getting infinite MPG during that time, however, you will not continue forward forever, and it took fuel to get up to that speed to begin with. You have to average over some distance, say, an entire tank of fuel, and see how far you get. Yes, during some of that trip, you will be engine-off-coasting, but during other parts of the trip you will be using fuel just like any other commuter out there.