That is a poor fuel consumption for an Hdi, Parkers guide gives 40 mpg which means you should get 50+ on a long run, this engine will do 60+ in a C5 but its obviously working a lot harder in the C9 as emissions are up and yours is in a higher tax group.

Firstly is you engine running at the correct temperature as running cold will adversly affect the consumption. If its smoking you could have an injector problem but to give that consumption it would need to be smoking all the time.

Driving style will obviously affect the consumption but unless you drive very agressivly you should get at least 40mpg on a long journey.

Its not an auto is it? That will knock the economy

Repaired one this week

customer complaint ,high fuel consumption,lack of power ,clouds of black smoke on high acceleration

plugged x431 into car came up with no real fault codes

further inspection found a split pipe that goes from air intake to turbo

pipe is 60mill in diameter and about 80 mill long ,follow air intake pipe down short pipe joins to plastic pipe that feeds turbo

at high revs the air that should be forced into the turbo was escaping through the split

so lots of unburnt fuel clouds of black smoke,low pressure to turbo resulting in a lack of power ,new pipe fitted ,power back , can hear turbo at 2500 revs, no black smoke

Srted