Diesel vs petrol cars

When weighing up the pros and cons of petrol and deisel, it's easy to feel lost.

The cost, environmental impact, and performance are all things you'll want to consider.

Working out which is better for your car can be a headache, but we're here to give you the facts. 

What's the difference between petrol and diesel cars?

There are a number of differences between petrol and diesel cars. Driving experience, cost, and the environment are all things to consider when working out what's best for you.

What's cheaper diesel or petrol cars?

Petrol cars are generally cheaper to buy and fill up than diesel cars. Though the difference in cost is usually fairly small. Check our petrol prices guide to find the price of petrol and diesel in your local area.

One of the main reasons that diesel cars are more expensive is the engine. Diesel cars ignite fuel by compressing it to a very high pressure rather than using a spark plug. A spark plug is a small part of a car's ignition system. It ignites the air and fuel mixture in the engine's combustion chamber, creating the power that makes the car move.

This means that the engine has to be stronger in a diesel car. There's also the extra cost of emission-control systems like diesel particulate systems and AdBlue. This is a diesel exhaust fluid that helps reduce nitrogen oxide emissions from diesel engines.

Running costs

There are a few factors that affect running costs. Let's go through each one and see how diesel and petrol compare:

• Insurance. Petrol and diesel are on a roughly even playing field when it comes to car insurance. A diesel car may have slightly higher insurance rates because of potentially high repair costs. Overall though, the difference is slim.
• Servicing. Because diesel cars have more systems, there's more things that could go wrong. Older diesel cars tend to have worse MOT pass rates than petrol cars, so this could lead to more expense.
• Fuel. Unleaded petrol tends to be more expensive per litre than diesel, diesel is usually more economical with fuel use. This is where petrol can fall short slightly. For high-mileage drivers, diesel has better fuel efficiency than petrol cars.
• Tax. Diesel cars generally emit less CO2 than petrol cars, but the difference is small. This can affect how much tax you pay. The current tax system works out your first-year rate by the amount of CO2 it emits. ULEZ (Ultra-Low Emission Zones) have also made it harder for diesel cars. For diesel cars to be compliant, they need to meet Euro 6 standards. Most diesel cars registered after September 2015 do meet these standards, but there are many that don't. Non-compliant cars are faced with a £12.50 daily charge to drive within these zones.
• Emissions. Older diesel cars can be polluting, and can emit more air pollutants like nitrogen dioxide (NO2). AdBlue and diesel particulate filters have helped to cut this down though. Diesel cars generally emit less CO2 than petrol, but the margins are small. Diesel engines are more efficient with fuel consumption, so they use less fuel to travel the same distance.
• AdBlue. This is diesel exhaust fluid (DEF) that helps to reduce harmful emissions. You'll need to refill this tank periodically. Currently it would cost around £20 to fill up a 10 litre AdBlue tank. The cost is still quite minor though, as 10 litres should last 3,000 to 6,000 miles. 

Purchase price

Diesel cars are typically more expensive to buy than petrol cars. This isn't always the case though, and the price can depend on the age, make, and model of the car.

For example, a used diesel car can be cheaper than a new petrol car.

Car value

Many factors can affect the value of your car in the UK market.

Petrol:

Petrol cars are extremely popular in the UK. They're cheaper to buy than diesel cars and can be more economic for shorter journeys and city driving. But they may be losing value compared to electric and hybrid cars due to ULEZ and Clean Air Zones.

Diesel:

The same can be said for diesel cars, as the UK gears up to ban the sale of new petrol and diesel cars from 2035.

Diesel cars can still be a good investment though, as they tend to fetch a greater MPG (miles per gallon) than other fuel types. Diesel cars can hold their value better over time, especially for larger models with high fuel efficiency and robust performance. 

Driving and Performance

There are a few differences between how petrol and diesel cars drive. Let's take a look through them:

• Noise. Diesel cars are typically noisier than petrol cars. Though diesel cars have become more refined in recent years, the engines are usually louder than a petrol car.
• Revs/engine speed. Petrol cars have a higher rev limit (how fast the engine can spin) than diesel cars.
• Power delivery/torque. Diesel cars produce less power than petrol. Torque is the measurement of a car engine's ability to generate rotational force and turn the wheels. It's what gives drivers the feel of power and control in a car. Diesel cars typially produce more torque than their petrol counterparts. This makes them great motorway cars, and more suited to towing caravans, for example. They don't need to work as hard to accelerate, especially at high speeds. These factors also explain why diesel cars use less fuel, as they're not having to work as hard to gain speed.
<liDiesel particulate filters. While diesel cars are great for high-mileage drivers, they can prove less effective for low-mileage drivers. This is due to diesel particulate filters (DPFs). DPFs absorb tiny soot particles from a diesel's exhaust, trapping it in a filter. The trapped soot needs to be burned off so that the filter doesn't get blocked. This can only be done when the engine is up to operating temperature, and the car's engine and speed is above a certain level. So if you're someone who mainly drives in town and don't usually go above 50mph, you may want to consider a petrol or electric car instead.  </li

What's the environmental impact of petrol and diesel cars?

The UK government have pushed back a ban on petrol and diesel cars from 2030 to 2035.

After 2035, dealers won't be able to sell new petrol and diesel cars. They'll only sell new zero-exhaust emission vehicles (electric cars and hydrogen cars).

At the moment, this legislation will only apply to new petrol and diesel cars. There's no indication that second-hand diesel and petrol cars will face any restrictions to their sale.

It's worth noting that the government could bring in fresh emission control standards before 2035, for example, they might bring in new low emission zones. At the moment though, almost all current zones work on a basis of legislating against pre-Euro 4 petrol cars, and pre-Euro 6 diesels.

But 2035 is still a long way off, so let's look at the environmental impact of both petrol and diesel.

Petrol

Petrol cars can have a significant impact on the environment. They emit carbon dioxide (CO2) and other greenhouse gases (GHGs). CO2 traps heat in the atmosphere which leads to global warming. They also produce methane and nitrous oxide, which are even more effective at trapping heat in the atmopshere than CO2.

The production and distribution of petrol cars also has a negative impact on the environment. Oil has to be extracted from the ground, transported to a refinery, and refined into gasoline. This creates harmful GHGs before it's even transported to our service stations.

Exhaust fumes from petrol cars also harms our health. These fumes contribute to the early deaths of around 40,000 people in the UK each year.

Diesel

Diesel cars also emit harmful pollutants, including nitrogen oxides (NOx), sulfur dioxide (SO2), and particulate matter (PM). These emissions can lead to smog and acid rain which damage crops, trees, and other vegetation.

Just like petrol, diesel cars also contribute to global warming by producing greenhouse gases. They do have lower CO2 emissions than their petrol counterparts though.

The emissions from diesel cars can still be harmful to health though, particularly for children and the elderly.

What are the pros and cons of petrol cars?

Let's recap the main advantages and disadvantages of petrol cars:

Advantages

• Petrol cars are usually cheaper to buy.
• Their engines are typically more refined.
• Cheaper fuel.
• Potentially higher MoT pass rates and lower servicing costs.
• Most have no DPF to clog. It's worth noting that some petrol cars now have particulate filters.

Disadvantages

• Higher fuel consumption. Petrol cars are less economical with fuel than diesel cars.
• Higher CO2 emissions.
• Not so well suited to towing.

What are the pros and cons of diesel cars?

And on the other side, here's the main advantages and disadvantages of diesel cars:

Advantages

• Better fuel efficiency than petrol cars.
• Good motorway performance.
• Lower CO2 emissions.
• The engines don't have to work as hard.
• Longer range between refuelling stops.
• Well suited to towing.

Disadvantages

• They're more expensive to buy.
• Potentially higher servicing costs and lower MoT pass rates.
• The DPFs can get clogged.
• Loud engine noise.

Older diesel models probably don't meet the emission standards for low emission zones.

Are electric and hybrid cars the future?

Now this is where it gets tricky. For many people, the shift towards electric and hybrid cars can be worrying. We all have different needs when it comes to buying a car. And we want to know that those needs can be met. Whether that's our budget, annual mileage, or our typical daily journeys. Let's take a look at what electric and hybrid cars can offer:

• A win for the environment: Electric and hybrid cars are more environmentally friendly than diesel or petrol. Electric cars (EVs) are better when it comes to the environment because they don't produce emissions while running.
• Fuel economy: Hybrid cars can be extremely economical when it comes to how much fuel they use. While a diesel car still tends to be best for long motorway trips, hybrid cars are great around town. Regular slowing and accelerating allows the batteries to recharge under braking.
• Cost: Full hybrids, or self-charging hybrids, are cheaper than plug-in hybrids.

One of the main concerns for electric cars is charging access, especially on longer trips. There's also the issue of how electric cars are made. Making lithium batteries also uses large amounts of energy.

Despite the manufacturing and their electricity source, EVs in the UK still have much lower carbon emissions than traditional cars. With the government set to ban the sale of all new petrol and diesel cars by 2035, sales of EVs are set to be on the rise. Before deciding whether to buy an EV, it’s important to consider many factors, such as your driving habits, charging access, and overall cost of ownership.

FAQs

Should I buy a second-hand diesel car in 2025?

Diesel cars retain their value well, but these values may be affected as the 2035 ban approaches.

They're good value for money though, but they can have higher taxes and charges overall.

Which is healthier petrol or diesel?

Petrol is generally healthier than diesel because diesel fumes are more damaging to your health. This is because diesel engines emit NO2 which can cause poor air quality in built up areas.

Diesel exhaust is a known human carcinogen according to The World Health Organization. Exposure to it can also trigger asthma attacks. Diesel can also irritate the skin, eyes, and respiratory system.

Is petrol cheaper than diesel?

Petrol is generally cheaper than diesel in the UK.

Diesel cars can be more economical with fuel use though. This makes them more cost-effective for long journeys.

Why do diesel engines get such a bad time?

There's a few reasons why diesel engines can get a bad rap. They may need more maintenance and troubleshooting than a petrol car.

Water, dirt, and other contaminants can enter the fuel system through a damaged tank or a poorly sealed fuel cap. Diesel injectors can also become clogged, causing the engine to work harder and overheat.

Diesel vehicles can be more expensive to fix due to modern filters and emission-busting systems.

Are diesel cars banned in London?

No, diesel cars aren't banned in London. But they might have to pay to enter London's ULEZ zones.

The ULEZ area has grown significantly since its introduction in 2019. It now applies to most of London and many of its suburbs. The sale of diesel cars has dropped by almost 40% since these measures have come into place.

Are diesel cars better than petrol?

This all depends on your personal driving habits, the environment, and your budget.

Diesel cars are usually more expensive to buy new than petrol cars. But they can be much more cost-effective when it comes to fuel economy.

If you're someone who regularly drives on the motorway, and for many long distances, diesel might be the better choice. For short-distance and city driving, petrol might suit you better.

When it comes to being environmentally friendly, diesel cars emit less CO2 than petrol cars. But petrol cars are generally better for the environment overall because they emit less NOx and particulate matter.

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