2008 Ford Focus Pricing and Specs

I'd say you're looking at two different problems here, neither one of which involves the actual fuel tank (which is, indeed, 55 litres). The first problem is more likely to be the calibration of your fuel gauge that is out. If the gauge isn't reading accurately, it will tell you the tank is emptier (or fuller) than it really is. Your car is actually doing what most fuel gauges do, which is to be a bit pessimistic, suggesting there's not as much fuel still in the tank as there really is. You could have the gauge recalibrated, or simply know that even when the needle is at empty, you've still got a buffer zone of fuel remaining.

The fuel consumption, meanwhile, is another issue and it's true to say that 20 litres for 140km of driving is too thirsty. A basic tune up might help, starting with fuel filters, air cleaners and spark plugs. But don't ignore things like correct tyres pressures and whether there's a roof rack fitted; these things will affect fuel economy more than you might imagine. And never under-estimate the affect driving style has on fuel use. A driver who smashes the throttle from every green light will soon start using more fuel every kilometre.

They might both be Ford Focuses, but they're a couple of generations apart meaning that they are not only physically different, they also used different transmissions to each other. Even if, by some miracle, the older gearbox would bolt to the newer engine, the car still wouldn't have the correct electronics to make the transmission work properly.

Even if the transmission in question was a manual which requires much less in the way of electronic control, the unit in the 2008 Focus was a five-speed, while the later car used a completely different six-speed. Even things like the clutch and flywheel would be incompatible. You'd probably even find the gear-shifter for each transmission enters the cabin in a physically different spot, meaning the interior trim would no longer fit.

Have the dealer give you the part number and name of the part required and see if you get it Ford in England or Germany, or even an independent parts supplier.