Driver tools Choosing between petrol and diesel

Petrol-and-diesel

Will a diesel car save you money in the long run? 

Boasting superior fuel economy and lower car tax, diesels have been considered the obvious choice for frugal motorists since the first mainstream diesel-powered cars appeared in the early 1980s. But with manufacturers asking a premium for diesel models, and the development of super-economical petrol engines and cheaper petrol prices, is diesel still the answer to cheaper motoring?

We look at the factors you should consider when deciding between a diesel or petrol model.

Read the full results of the petrol and diesel investigation to find out our petrol or diesel recommendations for the models we've tested. 

Both petrol and diesel now carry the same duty

Price differential is in favour of petrol these days

Petrol and diesel fuel prices

In the UK, diesel can be more expensive than petrol. With fuel pricing favouring petrol, and advances in petrol engine technology, making their efficiency ever closer to that of a diesel, there must be question marks over the diesel price premium - typically £1000 to £2000 more, for models of the same specification. 

It could take longer than you think to recoup the price premium on a diesel car - use our petrol and diesel fuel calculator to determine how long it will take.

In our petrol or diesel investigation we've picked identical-spec petrol and diesel versions of popular models and calculated the annual fuel bill for each. In four of our six examples, the petrol engine was the best choice for a driver covering around 11,000 miles a year. If you do fewer miles than this, petrol will almost always be the best choice.

Residual values of petrol and diesel cars

Diesel cars generally retain their value better than petrol versions. They’re currently in high demand, thanks to people looking for cars with better fuel economy and lower car tax rates. However, the 2012 Which? Car Survey shows, on the whole, that diesel-powered cars are still slightly less reliable than petrol ones. And while routine maintenance costs are similar for petrol and diesel, it is potentially more expensive to repair a diesel if anything serious goes wrong. In particular, diesel engines use particulate filters, which can get clogged (especially if only used for short journeys), and the cost of replacement can stretch into thousands of pounds.

Car tax, insurance and servicing costs

Diesel engines are inherently more efficient than their petrol opposites, so the CO2 levels are usually lower, resulting in correspondingly lower car tax liability. The difference in servicing costs, however, is negligible. 

The price of insurance can vary by model and can favour either option, so check before you buy.

Car tax and insurance should be factored into your estimations, but the difference will be small compared the likely fuel savings.

Diesel cars tend to have lower emissions

Diesels tend to have lower emissions than petrol cars

Petrol vs diesel – other factors to consider

  • Conventional wisdom says that petrol models tend to be faster, smoother and quieter than their diesel counterparts. However, diesel cars have become more refined, as carmakers have developed ways to mask the trademark signs - to the point where you may even struggle to tell the difference in some upmarket models. Often, the visible give away is the rev counter, which will have a much lower rev limit than one for a petrol car.
  • Diesel engines also offer increased torque (pulling power) from low revs, which is especially useful when towing or overtaking.
  • Diesel cars are more efficient, and so use less fuel for a given mileage, potentially causing less damage to the environment (especially if fitted with a diesel particulate filter to trap the nasty soot-like emissions many associate with diesels).

The Which? petrol or diesel investigation

Read the full results of the petrol and diesel investigation to find out our petrol or diesel recommendations for the models we've tested. 

We've picked identical-spec petrol and diesel versions of popular models and calculated the annual fuel bill for each base on the latest figures and tests.

More on this...

Other sections in this guide

  1. Overview
  2. Petrol and diesel fuel costs
  3. Choosing between petrol and diesel

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