With the majority of new cars sold in the UK are now running on Diesel – we ask the question: Are you really saving money by choosing a Diesel?

We agree that the headline fuel efficiency and MPG rating for today’s diesel powered cars are impressive, although sometimes hard to achieve if you are also not an avid Hypermiler. We are also not denying the road duty savings of many diesel cars compared to their petrol powered cousins. The real question is: will buying a diesel actually save you money. With diesel selling on average 5p a litre more than petrol, you might be surprised by the results.

To help sort this out, lets take the UK hottest selling car of the year – The Ford Fiesta. According Ford’s website, the cheapest petrol model Fiesta comes in at £9,795.00 (1.24 60PS) with the diesel version commanding £11,795.00 (1.4TDCI 70PS). That’s a £2000 premium for the derv engine.

Now we can work out the sums based on Mr Jones, driving an average of 12,000 miles a year and achieving the combined MPG figure (he’s not a Hypermiler)

Petrol Fiesta 52.3 MPG Combined
Total for 1st Year (inc purchase): £9,795.00 + £1397.78 fuel

Total:  £11192.78 + £100 road tax

Diesel Fiesta 70.6 MPG Combined
Total for 1st Year (inc purchase): £11,795.00 + £1070.66 fuel

Total: 12865.66 + £20 road tax

After one year you are still £1592.88 down by opting for the diesel an even with the diesel saving you £80 road tax a year its still going to take you 4.92 years to cover the costs of buying the Fiesta diesel. This is based on an annual saving of £407.12 a year on road tax and fuel at today’s average prices.

But what if you are a seasoned motorway driver that spends a lot of time behind the wheel? The petrol Fiesta will cost you 11.6p a mile while the diesel will cost 8.9p a mile, a saving of 2.7p a mile. The sums show that you’ll need to do a total of 71111 miles in the first year to break even and I’m quite certain that I’d rather not do that in a Fiesta!

So why are diesel cars more expensive? We asked Ford’s nice PR lady this very question with the following reply:

“The materials, equipment and technology in a diesel engine cost more than that in a petrol engine.

The range of petrol and diesel Fiestas available reflects our aim to give customers a choice when considering the initial cost of the car and its running costs.  Our aim is to give customers a good choice and range of vehicles and this bears out as we are able to maintain our position overall as Britain’s best-selling car and van manufacturer.

We don’t make recommendations to customers although we are able to give them reams of information through their dealer or on www.ford.co.uk where there are features and specifications charts to download. These include statistics for all engines. “

Most diesel engines these days are equipped with small high pressure turbo chargers and an array of emissions capture  systems to try and filter out the dirt and grime that comes with running diesel fuel. This does account for the some of the additional costs of the cars manufacturing but you have to wonder if the premium is really to justify the MPG gains to be had by choosing the diesel option. You can hear the nice salesman now, “Yes Mr Jones, the diesel option is more expensive but just think of the fuel saving and road tax you will save. The road tax is only £20 a year!”

To sum up, we have just one recommendation: Do YOUR sums. If you travel enough miles in the year to warrant a diesel then clatter away but if like the majority of motorists you only cover up to the average of 12,000 miles a year, you might want to think again about what engine graces your new car.

We’d love to hear about your thoughts on the matter of petrol vs diesel. Feel free to leave a comment below or join the discussion on our busy and very knowledgeable Hypermiling Forum.