Should I buy a second-hand diesel car?

There’s no denying, diesel cars are under the cosh at the moment. It seems that UK motorists are falling out of love with these less environmentally friendly vehicles fast.

However, despite changes in consumer behaviour and industry regulations, diesel cars still have a place on Britain’s roads and they’re not likely to be banned anytime soon.

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If you are thinking about buying a second-hand diesel car, here’s a handy list of things to think about:

Mileage considerations

If you are doing high motorway mileage, then a diesel may be a better choice for you. Somewhere in the region of 25,000 miles over three year is about right. However, if you’re driving less than 12,000 miles per year then you’re probably better off opting for a petrol car.

Doing more than 12,000 miles a year? Then the additional cost of a diesel car may be outweighed by the savings you make from its better fuel economy; especially if you’re buying a larger car. Petrol engines require a lot more fuel to get heavier vehicles moving.

Whether it's cost-effective for you will depend on the mileage that you do, as well as the specific price and fuel economy of the cars that you are considering.

If your long-distance driving takes you into towns and cities, there is a risk that paying to enter clean air zones will cancel out any fuel savings. To avoid that possibility, you may want to look at a newer diesel car that meets the Euro 6 emissions regulations. These vehicles won’t be affected by the forthcoming London emissions charges, and are expected to avoid other city emissions charges too.

Tough MOT

A tougher MOT came in at the back end of 2018, which focuses on diesel particulate filters (DPF). It states that all diesel cars made after 2009 must be fitted with these filters to pass strict emissions tests. DPFs can clog up and are expensive to repair or replace, so some owners have been tempted to remove them altogether. Under new rules, if the DPF shows signs of tampering in any way the car will fail its MOT.

Cars will also be failed if they produce any “visible smoke of any colour”, which could lead to many failures.
In a lot of cases, the cost of reinstating a DPF or replacing a broken one will be more than the car’s value meaning it is likely to be scrapped.

Tougher MOTs

Value for money

Since the VW diesel emissions scandal in 2015, sales of diesel cars has fallen to around 30% of the market for new vehicles. This is also thanks to higher tax costs and lower residual values as a result of government intervention in diesel.

Values of used diesel cars are starting to fall. According to HPI depreciation, based 3-years-old vehicles with 60,000 miles on the clock, on a diesel executive car is 62% versus 61% on a similar petrol model. The gap is greatest in the convertible market where a diesel convertible depreciation is 65% while an equivalent petrol model has a depreciation of 58%.

But there is unlikely to be ban on diesels in the near future and they are getting cheaper to buy. If you do high mileage and require excellent fuel economy, then a diesel could still be the car for you.

Larger vehicles

If you want an MPV or an SUV, then a diesel engine is the better choice. Torque and power at low revs means that fuel economy is better than on a similar petrol model and they’re easier to drive.

Diesel engines are more efficient than petrol models. In heavy cars, which need more energy to get moving, that difference adds up to greater savings.

The way that diesel engines work also makes them more suited to larger cars: you don't need to press the accelerator hard or rev the engine to feel a burst of power. Even a medium-size diesel engine is powerful enough to get a big and heavy sport utility vehicle (SUV) moving quickly, with little apparent effort.

In contrast, you need to rev many petrol cars to get that same surge of power, reducing fuel economy even further. It’s not uncommon for an SUV with a diesel engine to offer twice the fuel economy of the petrol version of the same vehicle.

That makes diesel the fuel of choice for people carriers, SUVs and pick-up trucks. Some hybrid SUVs combine a petrol engine with an electric motor, which offers impressive fuel economy on shorter journeys, but they aren't ideal for everyone because their efficiency quickly drops on longer trips and the cars are expensive.


Company cars

The new car tax system has reduced much of the advantage that diesel vehicles used to have because it’s no longer solely based on carbon dioxide emissions (CO2). This has reduced the incentive for drivers to buy diesel-powered cars.

However, the current company car tax regime is still linked to CO2, so you may make savings with a diesel vehicle.

It will have to be efficient, though, because rates for diesel cars are 4% higher than petrol vehicles. This makes small petrol cars cheaper for business users. But large diesel-powered cars, including SUVs, are more fuel-efficient than petrol versions, so they tend to attract cheaper rates of company car tax.


Caravan enthusiasts may want to consider diesel powered vehicles for similar reasons to those already mentioned.

Just as diesels are best at getting heavy vehicles moving, they are also the engine of choice for towing. Their pulling power (torque) is much more effective at hauling a heavy caravan or trailer away from standstill or up a hill.

Petrol engines in smaller cars may not be up to the job and stall on steep hills. Even if they can pull away, they will be thirsty at the pumps.


Got a diesel car and not sure what to do with it? You could consider a manufacturer’s diesel scrappage scheme. It’s a good way to trade in an older model for a cleaner eco-friendly model.

If you buy a diesel car registered from 1 September 2016 it will meet the Euro 6 emissions laws.

When you're buying a used car, it's worth checking which emission standard it meets. Some manufacturers only complied at the last minute – selling Euro 5 cars right up to September 2015, when Euro 6 became mandatory. But others sold Euro 6 compliant cars well in advance.

All diesel Mazda CX-5 models have met the standard since 2012, for example, and so should be exempt from inner city charges, based on current information.

Depending on your vehicle, you could be charged for driving in urban areas declared as ultra low emissions zones (ULEZ).
They are already operating in London and later in 2019 in Birmingham. Charges have also been confirmed for Glasgow.
Inner city clean air zones have been proposed for 16 towns and cities outside London, and are likely to focus on older diesel cars.

Looking to buy a used car? Why not have a read of our Used Car Checklist and find out everything you need to know when buying a car; be it petrol or diesel.