A car has to be fuel efficient. It means it has to completely burn the fuel.
Leaving it running burns more gas. Today's electronic fuel injection systems are much more efficient and do not flood the cylinder with gas until needed. Older motors, with carburetors, may burn excess gas at startup. That's where the idea comes from that it's better to leave it running.
Lighter weight, more aerodynamic, and more fuel efficient engines, transmissions, and tires.
Yes, the indirect injection is more fuel efficient because it provides stability to the engine.
No, it is less fuel efficient.
There hasn't really been a brand of semi trucks recognized as the most fuel efficient. Since they run on diesel a more efficient fuel, semi trucks already are more fuel efficient than cars in terms of size and power.
Driving with the windows down and AC off at lower speeds is more fuel efficient. At higher speeds(45+), having the windows down will create more drag and it is more efficient to have the windows up with the AC on.
Electric pumps are more efficient pushing versus pulling and the fuel cools the pump.Electric pumps are more efficient pushing versus pulling and the fuel cools the pump.
When it comes to fuel efficient and luxury cars the best bet is to compare hybrid-engine designs. More and more luxury car companies are now coming out with fuel efficient hybrid-engine designs.
A manual transmission civic is more fuel efficient than an automatic transmission. That goes for just about any car.