Every car enthusiast who plans to purchase a vehicle inevitably faces the question: "Which engine is better: petrol or diesel?". The truth is, there is no unequivocal answer since vehicles of any type have their advantages and disadvantages.
To make an informed choice, it's crucial to understand all the factors car fuel influences, from regular expenses to the vehicle's overall performance. In this guide, we've covered all the essential factors you should keep in mind when deciding between petrol and diesel.
Difference between petrol and diesel cars
There are significant differences between petrol and diesel vehicles, accommodating varying needs. Only by taking all of these distinctions into careful consideration can you ensure that the car you obtain will be a perfect fit for your lifestyle and goals.
Below is the list of key points, the importance of which you shouldn't underestimate:
As a general rule, and when buying a diesel car, you will pay a larger amount than you would have for its petrol counterpart.
Here are some examples:
- In November 2020, a petrol-powered 1 Series BMW at entry-level, the 118i SE, cost £24,965 in the UK. A diesel car of the same status, the 116d SE, was sold starting at £26,485.
- In 2021, a Ford Focus Titanium 1.5 litre TDCi diesel cost £680 more than a similarly powerful 1.0 litre EcoBoost petrol.
- The same year, a Volvo V40 Momentum D2 diesel was £1,860 more expensive than the T2 petrol model.
Diesel cars are typically more expensive to buy because their engines often require extra hardware compared to petrol vehicles. One such add-on is an AdBlue-reliant selective catalytic reduction (SCR) system, the aim of which is to convert harmful emissions into neutral ones.
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There are two main types of emissions that need to be taken into account when deciding whether you want to opt for an engine running on petrol or diesel - CO2 and NOx (nitrogen oxide). Generally speaking, diesel engines play a lesser part in CO2 emissions than petrol ones. However, keep in mind that the smaller the engine, the lower the CO2 emissions. This means that it's possible for a manufacturer's petrol-powered car to emit less carbon dioxide than a diesel vehicle.
Yet, as you compare engines of larger sizes, you'll notice that in similarly powered petrol and diesel cars, the latter typically demonstrate lower carbon emissions.
NOx emissions have an adverse impact on air quality and may cause severe respiratory health problems. Diesel vehicles are responsible for a higher percentage of NOx and soot-like particle emissions compared to those that run on petrol. That's why the above-mentioned AdBlue solution was invented to neutralise the harmful effect.
Expense-wise, the level of CO2 emissions determines the Benefit-in-Kind (BIK) and Vehicle Excise Duty (VED) tax rates. As for NOx, it is becoming a key factor to consider when paying for access to urban areas marked as Clean Air Zones, as well as surcharges like London's Toxicity Charge.
While unleaded petrol tends to be less expensive per litre than diesel, cars using the latter are known for being more economical with fuel use. Thus, in terms of fuel expenses, diesel-powered cars are a more budget/friendly choice in the long run.
Another factor that diesel vehicle owners should keep in mind apart from fuel costs and tax is the need for a regular supply of AdBlue. Although a five-litre bottle of this liquid typically costs approximately £5 at petrol stations and should last for about 3,000 miles, it is a recurring expense to consider.
Here are some average fuel economy figures, tested on 135 diesel engines and 169 petrol engines:
|Fuel type||Average mpg|
|Combined||Around town||Out of town||Motorway|
These numbers demonstrate that diesel vehicles outperform petrol ones in terms of fuel economy in every given environment.
However, a comparison of a Nissan Qashqai Tekna running costs over three years has shown the following results:
|Engine||Car price||Fuel economy||Value after 3 years||Running costs (10,000 miles / year)||Running costs (15,000 miles / year)|
|Diesel - 1.5 dCi 110||£25,910||70.6mpg||£10,882||£17,179||£18,253|
|Petrol - 1.2 DIG-T 115||£24,290||48.7mpg||£10,687||£16,720||£18,277|
Thus, if you're covering approximately 10,000 miles yearly on a previous-generation Nissan Qashqai, a car that runs on petrol will be a more economical choice. However, if you are planning to drive for longer distances, the diesel model proves to be cheaper.
All in all, there is no way of saying that one type of fuel is more economical than the other in all situations. The running costs depend on the car's usage, year of issue, and multiple other factors.
Therefore, when purchasing a car, you must have a clear plan on which purposes it will serve and how much it will be used.
When it comes to insurance costs, the car's engine size and market value will have a larger impact on the price than the type of fuel it uses.
Yet, a significant factor associated with diesel cars is higher costs of repair and replacement parts. This often means that owners of such vehicles are likely to pay more for insurance, as demonstrated in the figure below:
|Engine Type||Percentage||Average Annual Premiums|
The amount of road tax you will be paying for a petrol and diesel car depends on when it was first registered. The vehicle will maintain the initial tax rate even in the event of resale.
The existing tax systems in the UK are as follows:
- Before April 2017: This scheme uses official CO2 emissions as a basis for tax rates. Vehicles that produce no more than 100g/km of CO2 are exempt from car tax. Diesel and hybrid cars registered in this period experience low tax rates or are tax-free due to lower carbon emissions.
- After April 1, 2017: The owners of cars registered during this time frame only made the first payment based on CO2 emissions. After that, they are subject to a fixed rate that equals £155 per year (£145 for hybrid cars). The only cars exempt from car tax in this scheme are zero-emission vehicles.
- After April 1, 2018: Unless a diesel-engine car meets the Euro 6d standard, it will be subject to a higher tax rate during the first year.
- After January 1, 2021: At that time, Euro 6d became compulsory for all new cars sold in the UK, meaning that the owners of diesel cars that were registered after this date don't pay higher tax during the first year of ownership.
As you can see, if you own an older diesel vehicle, you may end up paying higher car tax.
There are some differences between driving petrol and diesel cars. For instance, the latter have more torque than their petrol counterparts, which means their pulling power is greater.
Thus, if you are an owner of a trailer or a caravan and need to tow it on a regular basis, a diesel vehicle is a sure winner. Yet, be prepared for the fact that diesel cars are rather noisy.
On the other hand, cars that run on petrol need more gear changes when overtaking. However, there are petrol engines that have entered the market fairly recently and provide many advantages similar to those of diesel engines and featuring fewer drawbacks.
Vehicles like this are designed to deliver more power with better fuel economy. Some examples of car brands using such petrol engines include Ford's 1.0-litre "EcoBoost" and Nissan's 1.3-litre "DIG-T."
As mentioned before, diesel cars have higher fuel efficiency than petrol ones. Besides, one litre of diesel fuel has approximately 15% more energy than a litre of petrol. Thus, a diesel car will typically need fewer refuelling stops on a long journey, with the efficiency of its engine being roughly 20% higher than that of a petrol car. This gives a significant advantage to diesel cars for long-distance travel.
If you plan to use your vehicle for low-speed journeys around town, it's almost always the right decision to go for a car that runs on petrol. Not only will it be cheaper but also more reliable than a diesel car, as the latter would require regular high-speed runs to keep its systems functioning properly.
What are the pros and cons of petrol?
If you live in an urban environment and don't go for long trips, it is worth considering getting a petrol car. Here is an overview of the advantages and disadvantages of such vehicles:
|Lower price||Less fuel-efficient than diesel cars|
|Short trip efficiency||Higher CO2 emissions|
|Less local air pollution|
|Low noise level|
|Good low-temperature tolerance|
The pros of getting a car that runs on petrol are:
- Lower price. Petrol is cheaper than diesel by approximately 2p per/litre. While it only saves you £1 per 50-litre fill, you'll notice the difference in the long run.
- Better for short trips. If you're looking to buy a car that will help you perform routine tasks like taking your kids to school or doing groceries, a petrol car is the ultimate solution.
- Less local air pollution. Vehicles fueled by petrol produce less particulate emissions that contribute to local pollution issues.
- Low noise level. When driving a car that runs on petrol, you'll feel fewer vibrations and hear less noise than you would've in a diesel-powered vehicle.
- Cheaper maintenance. Cars that use petrol are typically cheaper to maintain than the diesel ones, both with paperwork and automotive services, unless you put many kilometres on the vehicle.
- Good low-temperature tolerance. The freezing point of petrol is -60°C, making it impossible for the tank to freeze even during the coldest UK winter.
The disadvantages you may experience with a petrol car include:
- Less fuel-efficient. Even though petrol car owners pay less for fuel per litre, their vehicles consume more of it.
- Higher CO2 emissions. The ratio of carbon dioxide emitted by petrol cars is significantly higher than that of diesel vehicles. Since CO2 is linked to climate change and other environmental issues, such engines aren't the most eco-friendly choice, and they may also result in higher taxes.
What are the pros and cons of diesel?
Now that you've learned about the key advantages and disadvantages of petrol vehicles, let's take a closer look at diesel cars. Here are their main pros and cons:
|Great for long journeys||Higher purchase costs|
|Better fuel economy||May cause poor air quality|
|Lower CO2 emissions||Lower frost resistance|
|High torque||Expensive maintenance|
Some of the advantages of diesel vehicles are:
- Being great for long journeys. If you're in for long car trips, choose diesel over petrol engines since they provide more power at lower engine revs.
- Featuring better fuel economy. Diesel cars give their owners better mpg than their petrol counterparts due to their fuel containing more energy per litre.
- Lower CO2 emissions. Cars running on diesel produce less carbon dioxide emissions than equivalent petrol cars.
- High torque. Diesel cars are great for towing - take it into consideration if that's a task you need to perform often.
Despite all the pros of diesel fuel and the cars that use it, there are also some cons to keep in mind before you buy such a vehicle:
- Higher purchase costs. In the majority of cases, diesel cars cost more than their petrol equivalents.
- May cause poor air quality. Older diesel cars emit iNOx gases that may cause poor air quality in built-up areas.
- Low frost resistance. Diesel is prone to gelling in cold weather conditions.
- Expensive maintenance. If a repair is needed, fixing a diesel vehicle is likely to cost more due to modern filters and emission-busting systems.
What's the Future for Diesel Cars?
The UK government plans to fully transition to zero emissions vans and cars by 2035. This programme entails that in 2030 the sales of all new diesel and petrol cars will end. Although the proposed changes are still a few years away, the short-term future of diesel cars seems hazy.
Will diesel cars be banned?
Even though the timeline for banning the sales of petrol and diesel cars is already set, there have been no official plans to outlaw the use or resale of second-hand cars. However, the government's plan to minimise harmful environmental impact implies local councils taking such actions as:
- Changing road layouts at congestion points
- Stimulating the use of public transport and investing in low-emission buses
- Encouraging people to buy electric vehicles
If these measures don't prove to be successful, authorities can introduce local restrictions. Yet, if the emission levels decrease to the point of being legally compliant and there is no more risk of the legal thresholds being breached, the restrictions should be relieved.
Are electric and hybrid cars the future?
According to the Society of Motor Manufacturers and Traders (SMMT), diesel vehicle registrations dropped by 60% in 2020. There was a 47.5% decrease in petrol vehicle registrations and a 161% increase in battery-electric vehicle sales.
Besides, as a part of the ten-point plan for a green industrial revolution published at the end of 2020, the government undertook the initiative of equipping England's motorways and major A roads with approximately 6,000 high-powered charging points.
The UK government is also promised the following:
- Aiming to introduce a new low-emission regulatory regime in 2024.
- Investing £582 million for plug-in grants to reduce zero-emission vehicle sticker prices until at least 2022/23.
- Placing zero-emission cars in a favourable position with car tax rates until at least March 2025.
Thus, it is safe to say that electric and hybrid cars will be experiencing even more of an uplift than they do now.
Hybrid vehicles have two motors and use multiple sources of energy - combustible petroleum products and electricity. The powertrains work together to transfer power to the wheels through a complex transmission.
Usually, the electric motor assists the internal combustion engine in difficult situations, such as a steep road incline and when overtaking. It reduces the speed of the main engine, slows down its wear, and reduces fuel consumption.
Hybrid cars can go longer without refuelling and, consequently, have lower running costs. However, their purchase price turns out to be higher due to their complex mechanism.
As the name suggests, instead of an internal combustion engine, EVs use an electric motor with a battery as a power source. Its design is simpler than that of petrol or diesel engines since it has fewer moving parts and requires less maintenance. Such vehicles are safe for the environment, are virtually silent, have a high torque from low revs, and provide a great level of safety on the road. Their downsides include a limited power reserve, high price, sensitivity to cold temperatures, and a fairly small number of charging points.
Should I buy a diesel or petrol car?
So, after all, which car fuel option is better in the petrol vs. diesel pair? Which engine is more reliable? The answer depends on the requirements you have for your vehicle and the priorities you set - power or efficiency, low or high frost resistance, better performance for long or short-distance travel.
Or, perhaps, after weighing all the diesel-petrol pros and cons, you'll realise that you have to consider a more modern option to accommodate your needs, such as an electric car. Either way, after reading this guide, you have the knowledge you need to make a conscious and informed decision.
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