Iím quite difficult to impress when it comes to fuel economy, since December 2014 my average is close to 52 mpg. Iíve never fueled the car driven a longer trip in one go and then fueled again, but indications from the board computer after fueling and longer 70 mph trips have been up to over 62 mpg. The best so far between ďmulti tripĒ fuelings is 57,3 mpg, Iím not that convinced a small turbo-engine will do much better.
Details: Honda - Civic - 1,8 Comfort Edition - Spritmonitor.de
A small turbo engined petrol will not do better for out and out MPG
On a petrol the maintenance is cheaper and there will be less to go wrong (such as DPF etc..)
If you look as the possible MPG of the 1.5 turbo unit in comparison to the 1.6 then it does indeed make it tempting (especially when you consider the petrol will have a high BHP).
Lets say hypothetically that the Honda 1.5 gives the same economy as VAG's 1.4 TSI.
On a long Journey you're looking at 51mpg compared to 70mpg with the 1.6 IDTEC and around 58mpg with the 2.2 IDTEC On short journeys the petrol should give equivalent mpg to the diesel. Lets say you do 15k miles a year and i'll use the current price at my local Shell petrol station
1.5T VTEC = 1338 litres = £1378
1.6 IDTEC = 975 litres = £1073
2.2 IDTEC = 1177 litres = £1294
Lets say that you keep the car for 5 years. You can pretty much assume a clutch + DMF change in all 3 models (although less likely to fail in the petrol due to less torque) along with a DPF change in the diesels. Clutches/DMFs for petrols seem to be cheaper. Lets assume all the engines have an EGR that is equally reliable
DMF, clutch and DPF for the diesels - £2000
DMF and clutch for the Petrol - £900
So total cost in 5 years would be:
1.5T VTEC = £7790
1.6 IDTEC = £7365
2.2 IDTEC = £8470
The petrol will be lighter - so better handling and more mileage out of tyres
The petrol will heat up quicker - useful in the winter if you want warm air