What’s cheapest, diesel or petrol?

Driving is a pricey business. High fuel prices are forcing many motorists off the road, but drivers of diesel cars are having a particularly bad time, according to the AA.

In fact, it’s found that the average price of petrol in this country rose from 133.35 a litre in mid-May to 134.6p a month later. Meanwhile the cost of diesel rose from 138.17p a litre to 139.16p on average.

This might seem a bit unfair if you look at the rest of Europe, where diesel tends to be far cheaper than petrol. A report from the Post Office shows that diesel is 31p cheaper a litre in Holland.

But in the UK, in terms of fuel, it’s much more expensive to fill up a diesel vehicle. But working out whether a petrol or diesel car would be cheapest is a bit more complicated than just the price of the fuel in the tank.

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Running through the running costs

The cost of fuel is just one small aspect of the cost of a car. Insurance, depreciation, road tax and more, all these factors can change which type of engine is cheapest for you.

Even your specific driving style can have an impact on which type of engine is cheapest and certainly which kind of car is best - some experts believe that a turbo-charged petrol-fuelled car is best if you make lots of short journeys as the engine heats up very quickly, which can make a real difference in the winter.

However, if you often tow a caravan or trailer then a diesel can offer more torque (pulling force) with lower revs.

It’s worth visiting motoring forums to find out which kind of vehicle is most suited to your specific needs. But which is cheapest?

Fuel efficiency

Even though diesel is more expensive than petrol, diesel-powered cars are usually more efficient and use less fuel over the same journey.

To work out which is best, you’d need to consider the miles-per-gallon of each model. For example, the diesel-powered Fiat 500 achieves almost 14 miles per gallon more than the 1.2 petrol model.

However, it costs well over £2,000 more to buy the diesel model, so you’d need to drive tens of thousands of miles before you recovered the extra cost.

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Additional costs

Diesel-powered vehicles not only tend to cost more than petrol models but also, according to What Car?, are also pricier to service.

However, they can qualify for lower road tax and sometimes cheaper insurance. Of course, the price of insurance varies hugely depending on the model of car, so it’s always worth checking prices before you buy.

You can check the cost of a vehicle’s road tax on the Gov.uk website and compare car insurance prices online.

Even if you’re not stuck choosing a petrol or diesel-powered engine, it makes sense to check the affordability of a new car before handing over your cash.

Depreciation

How much a car loses or keeps its value is one of the biggest motoring costs but it’s all too easy to overlook when you’re buying a new car.

As a general rule, diesel-powered vehicles depreciate less than petrol cars. What Car? worked out that even though the Mazda 6 diesel version costs £1,100 more than the petrol model, lower taxes and depreciation means that it is £1,191 cheaper on average over a three-year period.

Check out the values of similar second-hand cars on a website like Autotrader to get an idea of whether a diesel-engine will retain significantly more value over the time you keep it.

Drivability

I regularly drive a diesel-powered Ford and a petrol-fuelled Vauxhall. There’s no doubt that the Ford is far louder (and more juddery, although that may well be my driving). Personally, I prefer the petrol engine.

However, our Ford is pretty ancient and I am told that diesel engines have massively improved over the last few years.

Browsing a few motoring forums, it’s clear that many drivers think petrol vehicles are simply more fun.

It’s also worth considering that diesel-powered cars are usually more expensive to repair. Diesel engines use particulate filters and these can get clogged – replacing them can cost thousands of pounds.

Some examples

The consumer champion Which? examined a number of popular vehicles to discover which was cheapest over three years or 36,000 miles.

For example, a diesel VW Golf is £442 cheaper on average over those three years, whereas the petrol Ford Fiesta was cheaper than the diesel engine, unless you kept it for more than eight years.

Overall, Which? found that the petrol engine was almost always the best choice for motorists covering 11,000 or less miles a year.

It has a useful tool that can help you work out whether you’d save money buying petrol or diesel, although it doesn’t factor in things like resale value. There’s a similar tool on the What Car? website.

There’s no rule of thumb to which kind of car is cheapest; too much depends on the specific model, how you drive it, how long you keep it and the number of miles you’ll cover in a year. But there’s no doubt that making the wrong choice could end up costing you.

My advice? Once you’ve decided on the make and model(s) you’re looking at, spend a few minutes checking out the numbers online to see if it’s worth paying more for the diesel – you could save yourself hundreds of pounds.

What do you think? Have you found one cheaper than the other? Is it worth paying more for a car that’s more fun to drive? Have your say using the comments below.