There has been a lot of talk regarding petrol vs diesel engines recently so JGS4X4 looks into the story and where we go from here. In the past, we were all pushed to buy Diesel cars thanks to superior fuel economy and less tax. However new diesel cars no longer benefit from low car tax, and with the new ban on Diesel cars in 2040 values are set to decrease.
Increased concerns over air pollution from diesel cars, is it still the right car to choose?
Diesel engines were widely promoted by the government in recent years as they emit on average 20-25% less CO2 emissions than their petrol counterparts, however, this view has seen a shift following more awareness on NOx pollution. It is important to note that current diesel engines are some of the cleanest ever produced.
Oxides of Nitrogen (NO and NO2) are produced as a by-product of internal combustion (in engines). These Oxides of Nitrogen – NOx gases as they are known – and related hydrocarbons and other pollutants have been linked to respiratory problems, smog and poor air quality.
Whilst diesel engines produce less CO2 on average than petrol engines, they produce more NOx. In modern diesel’s, Diesel Exhaust Fluid (DEF) – also known as AdBlue – is used within a Selective Catalytic Reduction (SCR) system to convert NOx back to Nitrogen and Oxygen. Older diesel engines, built before the latest EU6 emission standards were introduced, can produce much more NOx and particulates than the EU6 diesel engines, as they do not have this SCR technology.
Petrol and Diesel – What is the difference?
Due to their low-speed torque diesel cars deliver an effortless, relaxing drive. The narrow power band allows you to change up through the gears earlier and generate significant acceleration, making towing or carrying a large number of passengers much easier.
In the past, there has been a misunderstanding that diesel engines are slower, noisier and more expensive to run than petrol vehicles. However engineering advancements and technologies now inbuilt in diesel engines, means the difference between the two is now barely noticeable.
The widely spread power band in a petrol engine typically requires higher engine speeds to deliver similar torque as a diesel, but the top-end power of a petrol offers a smooth and responsive drive which some drivers prefer.
Car Tax – Diesel vs petrol
How much car tax you pay depends on when you bought your new car.
- Before April 2017: diesel cars are usually cheaper than comparable petrol cars.
- 1 April 2017 onwards: only the first year’s payment is based on CO2 emissions (diesel cars have lower levels of CO2 to comparable petrol cars).
In previous years, diesel cars generally retained their value better than petrol versions. This was thanks to better fuel economy and lower car tax rates. But since 1 April 2017, diesel cars no longer benefit from lower car tax. After two years, owners pay a standard rate of £140 per year. This means a large part of the savings offered by diesel engines has now been swallowed by the change in car-tax rates.
Still not sure if you should choose petrol or diesel?
Before buying any vehicle, you should take into consideration your day to day driving habits. Diesel vehicles come into their own on longer journeys at higher speeds but aren’t necessarily the best choice if your usual drive consists of shorter journeys or regular stopping and starting while held up in traffic in a town or city.
If you are driving more than 12,000 miles a year, a diesel is likely to be the most cost-effective choice. The higher energy density of the fuel and the way energy is released during combustion means diesel can offer a greater return on mileage.
One unique issue for diesel cars is the diesel particulate filter (DPF), which can get clogged. The filter cuts down on harmful particulate emissions from diesel engines being released into the air, but there are many reported cases of these becoming clogged and needing replacement. Most owners’ handbooks advise running the engine at high speed, for example on a motorway run, to keep the filter clear to avoid this. If your DPF does need replacement, the cost can run into thousands of pounds!
How will changes in legislation around diesel affect me?
Diesel cars driven in urban areas are likely to incur additional costs over the coming two or three years, over and above those imposed on petrol or alternative fuelled vehicles, an example of which is T-Charge.
However, owners of newer diesel vehicles which meet the latest EU6 emissions standards will not be penalised in the same way as older less environmentally-friendly diesel vehicles.
All of Land Rover diesel vehicles sold since September 2015 in the EU and EEA markets, meet these EU6 standards.
Will diesel cars be banned?
Yes, the sale of new diesel and petrol cars will be banned in 2040. This was announced as part of the UK Air Quality plan published on the 26 July 2017. The government’s plan requires local councils to reduce vehicle emissions in their area, using a range of measures such as:
- Changing road layouts at congestion and air pollution pinch points
- Encouraging people to buy electric vehicles
- Retro-fitting buses to give lower emissions
- Investing in new low-emission buses
- Encouraging the use of public transport.
If these measures fail, local authorities could introduce restrictions, such as charging zones or stopping certain cars from using designated roads at set times. However, the plan also states that these restrictions should be removed in the event that emission levels fall enough to be legally compliant and ‘there is no risk of legal limits being breached again’.
Several cities around the world have committed to banning diesel cars by 2025.
Ultimately, the decision you make when it comes to buying diesel or petrol is down to you. Factors such as regular journey type, where you drive and the type of vehicle will be the biggest considerations.
When it comes to considering the environmental effects when making your choice, modern technology means the impact of emissions from diesel and petrol are lower than ever before.