I know that there have been numerous threads over the last few months about how accurate (or inaccurate) the OBC can be, so I thought I would let you have my latest results from my Xmas & New Year trip to Southern Spain.
Car is '56' Siggy Elite 1.9 - Cdti - 18" Wheels - approx 16000 miles (Climate Control on all of the time and Cruise control on approx half the time).
Travelled down Fri 21st - Sun 23rd December and travelled back Thu 3rd - Sat 5th Jan - 2 people, plenty of luggage and our dog!!! Car not used whilst staying at our destination in Spain as we have a motor at our place down there so used that instead (Seat Altea 1.9). No major hold ups etc. to affect economy.
When I got home earlier today I filled up with diesel and noted the details on the OBC. They read:
Total Mileage: 3461.9 miles
Average Speed: 61mph
Gallons Used: 83.4
Average MPG - 41.5
Checking these against the receipts for fuel purchased I find that I had bought a total of 379.56 litres (83.6 Gallons), which equates to 41.41 mpg.
As you may see, the OBC could not have been much more accurate.
I personally think that 41.41 mpg for that length/type of journey is very acceptable. I am sure that if I had not used Cruise Control as much as I did the figures would have been better - on some of the long, straight roads I did see that maintaining the same speed by throttle yielded a higher 'rolling' mpg figure than having the CC set to the same speed (I had to do something to relieve the boredom!).
Overall costs of the journey were £172 return for the Eurotunnel, £349 diesel and approx £110 for road tolls.
Incidentally, the in built Sat Nav (with only main EU roads) was excellent - took me within 20 miles of our place in Spain (I knew the rest of the way anyhow) without any hassle at all!