Recently, you might have answered the diesel or petrol question with diesel. After all, those cars returned the highest mpg for years, and they built a reputation for longevity in many models. But things have changed. Ignoring, for now, the option of electric cars – which fuel is best for your needs now?
Considering the immense diversity of used cars for sale in the UK, drivers can pick and choose styles, performance and fuel types no matter what their taste. Even something like a modern classic SAAB 9-3 Convertible can be found with petrol or diesel options, and when it comes to family MPVs and SUVs there’s usually a petrol version to be found in the piles of diesel derivatives.
Which one is right for you depends on a number of factors, but as a rule, if you only do short drives petrol is better overall. Or a plug-in hybrid, really.
If you do small runs infrequently, you might think diesel is the better option – but it takes longer to warm up and pollutes more while doing so. The price difference at the pump means you won’t save much money, particularly if the car hasn’t been maintained well. Remember to check the MOT history when looking for used cars and watch for emissions-related failures; all you need is the registration number.
For the everyday, family car:
The case for diesel is strong for an every day, hard working car. The torque on offer means that a relatively small engine can feel brisk even with everyone on board and some luggage, and the allure of higher mpg is hard to resist. Depending on the age of car you are looking at, diesel models tend to be harder on their gearboxes and suspension as well as the engine itself needing more maintenance, and newer cars need regular top ups of AdBlue.
The case against diesel is, generally, driven by that maintenance cost on a used car. Aside from the fact that older diesels attract ULEZ charges in London when a similar age of petrol car won’t, the common failures of injector pumps, dual-mass flywheels and turbochargers, and the generally sooty, mucky nature of the fuel being burned makes keeping an older diesel car in top health an expensive exercise. Remember, too, that most recent diesel cars have particulate filters that only clean themselves on long, fast runs.
The case for petrol has, traditionally been weak since diesels arrived. They’re thirsty when cold; even a small engine is doing around 10mpg for the first couple of miles. The engines are often lighter and more highly tuned, feeling less robust. And for a lot of older designs you have to rev them to match the pace of modern traffic. However, the emissions are less toxic – hence London’s ULEZ allowing cars as old as 2005 – and once up to temperature the engines are usually efficient and quiet. Unless they’ve been thrashed, gearboxes and clutches tend to last longer, too.
The case against petrol can be seen at the pumps. Older petrol cars may need E5 or Super Unleaded, and for short trips that fuel won’t last long at all. Their emissions equipment is simpler, but in some areas the catalytic convertors are highly prized and stolen regularly.
So which is best? As a rule of thumb, the older the car that’s suitable for you – back to the end of the 1990s – a well maintained diesel is still a good choice, then consider the petrol versions unless you are in London, when the petrol is the only realistic choice. If you’re looking at nearly new or used cars from 2016 onwards, small economical petrol engines became popular and these are by far the better choice, avoiding AdBlue and other systems and delivering comparable economy once warmed up.
For a hard-working commuter car:
If you rely on your car for miles of driving every day, diesel is still a better choice. When the right choice of big Mercedes or BMW diesel can achieve over 50mpg at motorway speeds it’s hard to ignore, and some Audis can achieve 60mpg. However, don’t reject the modern small turbo petrol engine – while you won’t often see more than 40mpg, some models such as the Skoda Octavia 1.0-litre can match a diesel while being quieter and cleaner to live with.
For modern classic cars:
There are more potential diesel classic cars than ever. If you want a car for fun, there’s plenty to recommend going for a 1990s diesel, particularly if you want to undergo long journeys. However, remember that many cities are banning them now, particularly in Europe, so that Beetle TDI Cabriolet may not be quite as amusing as you first thought. Some Mercedes diesels are very impressive, though, particularly the straight six.
However, a petrol engine is usually easier to work on. Familiar things like spark plugs and simple means of pumping fuel make diagnosis of faults easier even in the age of computers and sensors. Aside from the need to stick with E5 fuel and its associated costs, we think petrol is still the way to go for your classic or fun car.
But which fuel is best overall?
So which is best? Diesel or petrol, the choice really depends on how you use your car and whether you are subject to emissions-based charging. As a rule though, petrol cars under six years old are the most versatile and sensible choice these days.
These days there’s a great argument for looking beyond those two fuels and considering hybrid, plug-in hybrid or even electric models. Although diesel and petrol new car sales end in 2030, many manufacturers are ahead of the deadline and electrifying their ranges, so whatever you choose, the next question may be ‘combustion engine, or electric’.