My MK4 Mondeo computer was ridiculous. Would often show 10-15mpg more than it was doing, it did get much worse after it was remapped though which was odd.

My car has a 50 litre tank. At 45mpg this would yeild me a range of 500miles. At current fuel prices (Petrol at 114.9p/l) a tank would cost me £57.45. That equates to 11.5p/mile.

I average 62mpg on my commute quite easily. That means my 50 litre tank yeilds me a range of around 680miles. At current fuel prices (Diesel at 117.9p/l) a tank would cost me £58.95. That equates to 8.5p/mile.

I probably average 25000miles per year. That means a petrol at todays fuel prices would cost me £2,875 a year in fuel. My diesel at todays fuel prices costs me £2,125 per year. That's a saving every year of £750... or a turbo, a set of injectors or a high pressure pump if it was to ever fail. The same items that are also present on a modern common rail petrol engine. Bare in mind my Focus costs exactly the same to service as a petrol equivalent and the intervals are the same. I also save on tax which is free on my Focus and not so free on the petrol engined equivalents.

I don't doubt diesel engines have emmisions control equiptment which is far more complicated than that of a petrol and also far more likely to go wrong BUT I've done well in excess of 150k in diesel engined vehicles since I passed my test 6 years ago and so far I've yet to have a big bill from a diesel.

I think the only time you are ever going to have issues with a diesel is if you don't drive them properly. Far too many people pootle around everywhere at 1500rpm and use them for town mileage. My car spends 95% of it's life on motorways and I try to run it right up the revs at full throttle at least once a day. I also use Millers Ecomax relgiously as I have done since I passed my test which I'm sure helps.

Going back to the conversion. If I could find a breaker with a written off V40 D3 or D4 I could pick up an engine & gearbox for £1,500 and I'm sure I could get all the other bits I required for a further £1,000. I would then estimate another £500 for programing works to get the new ECU to talk to the Focus' BSI/BCM. Around £3000 and that would yeild me 200bhp, a 5pot rumble, a small increase in fuel economy (or maybe not) and something completley unique. Also add into the equation I'll have a low mileage 1.5TDCi engine & gearbox to sell along with all the ancillaries which may return me maybe £750-£1000.

If I wanted more power out of my current engine I'd need to look at a hybrid turbo (£1000), aftermarket intercooler (£500), intake modifications (£300), exhaust system (£400) and a remap (£300) and none of you would bat an eyelid and I'd probably just about get 185bhp.