Should your next car be a petrol or diesel?

How does the total cost of ownership vary between the two?


When I first came into the motor trade diesel engines used to be noisy, smelly and somewhat agricultural. Then technology came in and car manufacturers made the engines cleaner, more powerful and refined, and with diesel cheaper than petrol at the pumps, diesel suddenly became more viable. Not for long however with the Chancellor making diesel pricier than petrol, choosing between the two fuel forms is now no longer that clear.

Increased cost of buying a diesel

If it was purely down to miles per gallon, diesel would win easily. A Ford Fiesta 1.4 diesel returns a quoted consumption of 69mpg. The petrol equivalent of the same capacity does 49mpg.

But the petrol hits back with the model costing less to buy. The petrol Fiesta in three-door Edge trim would set you back £12,195. The diesel version costs £12,995. And the difference isn?t going to get smaller.

Diesel engines are getting more expensive to build due to increased legislation. In 2011 a diesel particulate filter (DPF) had to be fitted to the exhaust to catch the soot that you normally see coming out of the back. That also required an injection upgrade and there are more changes coming next year. It?ll all add up to making the payback period for diesel longer.

Increased cost of maintaining a diesel

For vehicles fitted with a DPF we have noticed that some customers, mainly those that do short journeys, are experiencing problems with them as the filter does not get hot enough to clear itself out

They are also having problems with something called an EGR valve that sits in the air intake system and gets clogged up. Both of these require time to diagnose and can be expensive to repair or replace. As an example our works Transit Connect van we bought second hand, required a new EGR valve and just the cost of the part was £300.

Fuel cost comparisons

On average the price of diesel is around 6.72p per litre higher than petrol. So a typical small car fill up of 40 litres on a diesel car will set you back £2.69 more than petrol every time. Assuming you fill up once a week, over a year diesel will cost you £139.88 more. However on the Fiesta diesel I was talking about you only have to pay £20 a year in vehicle excise duty (because it emits less emissions) where as the petrol Fiesta you have to pay £115

So assuming that lower tax for diesels goes some way to cancelling the inflated pump prices, the best fuel choice comes down to the number of miles you cover and the depreciation of the car

To sum up

I read recently that an Andrew Fraser who works for Ford said: "We think a diesel makes sense from around 15,000 miles a year upwards."

However, I subscribe to the Consumer organisation Which? And on their web site it has a calculator which uses the price of fuel and car purchase price to calculate a break-even point. Using our Ford Fiesta example, at an annual mileage of 20,000 it would take over a year for the diesel to recoup the extra outlay compared with the petrol model. If you only cover 6,000 miles annually, the calculator says it?ll take four years.

So for me with our experience on the repair side and the research I have found the choice of whether to buy a petrol or diesel is clear. At the moment, for low-mileage, town-dwelling driver?s, petrol is the fuel of choice. For covering lots of miles on the open road, diesel does the job best.

That's it - If you've got a motoring question or could give us some comments, I would love to hear from you