So on my undulating, but typically uphill, return journey from work I've recently be struggling to make 50mpg - air temp about 10C.

Yesterday on the way home (air temp 17C) fuel economy seemed better at 56mpg and the car a bit more lively.

That seems a vast improvement for what is only really a few degrees warmer. Does this seem normal or is there an air temperature sensor that could be faulty?

Performance should be better on a cold winters day (not that you could use it anyways lol)

Performance should be better on a cold winters day (not that you could use it anyways lol)

And fuel consumption will be worse. The colder the air, the denser it is and therefore the more fuel that can be burnt.

And fuel consumption will be worse. The colder the air, the denser it is and therefore the more fuel that can be burnt.

Hmm I've heard that said before, but this car has always been the opposite.

My vrs always performs better in the colder temps but gets better mpg's in the warmer temps. Most of my previous cars have been like this too.

Hmm I've heard that said before, but this car has always been the opposite.

I see changes in mpg that match the change in temp, so I get better mpg in the summer. If I look at mpg over the course of a year it is quite obvious.

There is also a question as to whether the diesel composition is different in winter vs summer and what difference this could make to mpg.

You will get ever so slightly better performance and worse mpg in cold weather and when there is moisture in the air. Not that I've ever noticed more than 1 or 2 mpg difference though.

The difference in mine was quite pronounced - is there any sensor I should be suspiciuos of, or is it just one of those things?

Could be the coolant temperature sensor.

How long is the journey?

If it's short, then this normal. When the engine is cold it uses more fuel. If it takes longer to warm up, your mpg will be lower.

How long is the journey?

If it's short, then this normal. When the engine is cold it uses more fuel. If it takes longer to warm up, your mpg will be lower.

30miles. Have replaced the CTS recently so I don't think it's that. It's probably nothing TBH - I'm just being paranoid I suspect.