In recent years, petrol engine technology has vastly improved, so many petrol engines now offer similar or better mileage performance compared to diesels.
For years, assumed wisdom said that diesel cars were the most economical choice, delivering higher mpg figures than equivalent petrol cars. This is still the case for diesels such as Peugeot’s e-HDi range, which can deliver an astonishing 94.2mpg with just 84g/km CO2 emissions and still has 120BHP.
Many petrol engines now have lower emissions and higher power output. Take Ford's award-winning Ecoboost engine, which, even with an engine size of one litre, can power a Fiesta from 0-62 in 11.2 seconds, and generate 100BHP at up to 74mpg. These engines use turbo chargers and fuel injection to provide impressive performance.
To choose between petrol and diesel power, you must look at the type of driving you do in your vehicle. If it’s mainly city driving, with short journeys and a lot of time spent in start-stop traffic, diesel is not the best choice. If this is your routine, you should choose a petrol-engined car. This is because of new technology fitted to diesel engines.
Since 2009, Diesels sold in in Europe have included a Diesel Particulate Filter (DPF), which is part of the vehicle’s exhaust system. This filter traps “soot” created during the normal operation of the diesel engine. In order to meet European legislation, all vehicle manufacturers fit a filter to clean up exhaust gasses, so the days of black smoke blowing from diesel exhausts become history.
However, for the DPF to work properly, it has to heat up enough to burn off trapped soot particles. If you drive on A-roads, motorways or dual carriageways at speeds above 40mph, the filter can do its work in perhaps 10 minutes. If you make only short journeys at low speeds, the filter will not reach a temperature to remove soot and 'regenerate' or clean itself. So most manufacturers recommend that you drive a diesel car for 10-15 minutes at speeds above 40mph from time to time, so that the filter cleans itself before any problems arise, or a warning light appears on the dashboard.
Your weekday driving habits - when you may be doing school runs and driving to and from nearby work - is probably different from weekends. Then, you may visit relatives and friends, or drive on faster roads on shopping trips - so if this is your driving routine, the filter can regenerate and clean itself.
It’s important that you follow handbook instructions to regenerate the diesel filter, as the cost of cleaning or replacing the filter at a garage would not be covered under the vehicle's warranty - and these costs are high. So if you only drive on short journeys, or live in a busy city, a petrol car is your best choice.
Whether diesel or petrol power suits your typical journeys best, you should consider a hybrid car. A hybrid system stores energy generated during braking and deceleration in a rechargeable battery, which is used to power the car instead of burning fuel to improve economy.
An added bonus is that hybrids typically achieve their best fuel economy when used for city driving. For example, the Toyota Yaris, urban cycle gives 91mpg, 11mpg above its extra urban mileage figure. So for city drivers, a petrol hybrid is the smart option.
Read more about Diesel Particulate Filters (from the AA)