[Tannaton]

The other point to mention is that the in car gauge can vary - the only way to know the true MPG is to brim the tank, drive the car, brim the tank again and calculate it.

There isn't much you can do - removing the EGR sometimes gives a small increase in MPG but that's controversial, and might one day be an MOT fail.

Cleaning the inlet manifold sometimes helps but with only 60k on your car it's unlikely to need it.

The "go faster" fuels never recover in gains what they cost.

The cheapest and easiest thing is keep your tyre pressures to the Eco setting (38 psi I think) and choose your tyres carefully (check the labels). This makes more of a difference than most people realise.

I can't explain the technical reason why but modern diesel engines do become less efficient in colder temperatures - my XC60 drops 3 mpg at least, plus another 2 for the winter tyres.