Diesel never has been cost effective if you only do low annual milages. Bear
in mind also that the new Focus diesel, in line with many others, has a
diesel particulate filter fitted. This makes it unsuitable for doing lots
of short, low speed runs without some faster use in between.

I can't vouch for its accuracy, but there is a lot of data here:

http://www.carpages.co.uk/guide/ford/ford-focus-guide.asp

HTH

Chris

Without any doubt diesel wins every time because the engine is so much more
efficient. You will get at least a 25% increase in mileage per gallon of
fuel... and for the 1.6 this should be maybe as high as 50% increase in
mileage. The only thing that annoys me is that the few pennies difference in
petrol versus diesel prices has increased to 10's of pennies
difference!...but it is still worthwhile going diesel.

Beware of the dual-mass flywheel issue.   Don't know if Focus diesels
still use them, but my 2003 1.8TDCi certainly did;  it lasted 50k
miles before self destructing and landing me with a four-figure bill.
Rather common, apparently - see Honest John among other references, or
ask your Ford dealer's service manager.   Not just Ford, either, these
things are found on many modern diesels to make them behave more like
a petrol engine, i.e. smoother.   As others have said, if you're doing
a big mileage, the reduced fuel consumption and a three-year warranty
will make it worthwhile.   Otherwise, avoid the diesels unless
something's changed.

I still have the TDCi, by the way, and it does 39mpg.

My (56) 1.8 TDCi hatch will happily do 500 miles to a tank before flashing
up the 50 mile warning light, but many things need to be taken into account
to make a definative judgement.

Purchase price, ownership duration, annual mileage, residual value, fuel
costs, driving style, road fund licence all have an effect...

If you're doing 3,000 miles per year and you're the car for 10 years then
you're probably better off financially with the petrol; whereas if you're
covering 30,000 miles pa and only keeping it for 2 years then the diesel
will no doubt cost less...

Do the maths. The Diesel should return 45-50mpg, the petrol will be closer
to 30-35.

I have a 2006 Focus Mk2 1.6 T-VCT Petrol. I am currently getting 44.3mpg,
over 530 miles per tank.

Secrets? - 1) DON'T use supermarket petrol - I used to get 33mpg using
Tesco's
               - 2) Train yourself to accelerate SLOWLY (unless a real
emergency)
               - 3) Think ahead - sharp corner ahead? - take foot off go
pedal and aim to hit corner at a speed you can take safely WITHOUT braking.
Look ahead to traffic lights - red? do the same. Avoid braking as much as
possible - braking is WASTED energy - LOTS - preserve your momentum.
               - 4) Stick to 70 - 75 mph on motorways, even an extra 1 mph
at that speed is a dramatic increase in fuel consumption.

       THINK - what am I going to do with the extra minute I have saved
when I have arrived?

In general, if you think ahead and treat driving as a game of chess it
becomes truly more enjoyable and you can get to your destination in the same
amount of time, refreshed.