Understanding the efficiency number.

[Nova]

I'm in a bit of a predicament.
For whatever reason, my game tells me the fuel efficiency of an engine in %...?

I have no clue what it's supposed to mean, is it how many % of my journey I can get through before my tank runs out? :D

I have tried switching it from 1/100KM to MPG, yet it never changes.
So for now I'm stuck with a numbering system I have no way of understanding, can anyone help?
Cheers.

[Admiral Obvious]

The efficiency percent is thermal efficiency of the engine, which in effect means what percentage of the fuel is turned into actual work, while the rest of the energy is either unburnt fuel, or wasted as heat. Last I checked it was an average of the specific efficiency in between 1500 RPM and 2500 RPM.

L/100KM and MPG are both used for when you actually insert the engine into the car and run it down a road.

[Killrob]

Correct, currently the engine efficiency % is its average fuel efficiency between 1500 and 2500 RPM.

To add to what Admiral has pointed out: if you take a super fuel efficient car's engine, and put that into a Hummer, then that doesn't make the Hummer get good mileage, but fuel efficient it would still be (unless driven around at 6000 RPM or so). Understanding the difference between fuel efficiency and mileage is important.

[Nova]

Ah, thanks a lot guys, really helped me there.
Cheers. :)