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It’s all-change in the world of buying, selling and running a motor vehicle. Legislation already passed in the UK means that diesel vehicles will be banned from 2040 and other countries are likely to follow suit eventually, if they haven’t done so already. Germany, Ireland, India and the Netherlands have already set an even tighter schedule, planning to affect the ban by 2030.

Whenever it finally happens where you live, there is still a full range of options open to most car buyers when it comes to choosing the type of fuel the vehicle will run on. In the unlikely event of your vehicle still being functional in 20+ years’ time then there is a chance that you might not be able to use it anymore, but that’s a risk that we will all just have to take, unless of course we can buy an electric car and they still are not available in sufficient numbers to be a realistic option for everyone.

What Are The Relative Benefits of Diesel vs Petrol-Based Engines?

The answer to this will depend to a large extent on where you live. In the USA and the UK diesel is slightly more expensive than petrol. The rest of Europe is a mixed bag with each country being slightly different and petrol being more expensive than diesel in most countries, but usually the difference is only slight.

Diesel engines are generally more expensive than petrol engines so vehicles will be priced accordingly, and you will usually pay more for a diesel version of a car compared to the price of the same car with a petrol engine of similar size and power.

Choosing Petrol Vs Diesel 

The main criteria for most people will be the MPG (miles per gallon) obtained from the vehicle.

The mileage you get from a typical diesel vehicle compared to a similar petrol vehicle is usually higher – not massively so but over time it is enough to make a diesel engine more economical, given that the number of miles covered is sufficient.

For the purposes of illustrating this we have chosen a very popular vehicle from VW; the Golf Match.

Petrol Engine Version: – 1.4 TSI 122hp

The value after 3 years will be approximately 40% of new car price, depending on mileage and condition.

Diesel Engine Version: – 2.0 TDI 140hp

Note that the diesel version has a higher horsepower, 140hp vs 122hp thereby delivering more power to the road. The value of the diesel version will be, after 3 years, approximately 45% of the new car price depending on mileage and condition.

Therefore, diesel vehicles can be said to keep their value slightly better than petrol ones, but this can vary a lot and future legislation is likely to affect it considerably.

VW Golf comparison

Model Urban MPG Combined MPG
Petrol Version 1.4 TSI 34.4 45.6
Deisel Version 2.0 TDI 46.3 58.9

 

So, the diesel car is more expensive to buy when new, but it should be worth more, after, say, three years than the petrol version, everything else being equal. Obviously, you would need to make a realistic estimate of your likely annual mileage in order to work out whether the additional MPG obtained from a diesel engine version, and the savings in fuel used, would make up for the higher initial cost of the diesel engine option.

Research has shown that for those covering average, or less than average, annual mileage it can take between 4 and 10 years to recoup the extra cost of a diesel engine version of a vehicle so the headline figure of a higher MPG for a diesel engine vehicle may be misleading. Obviously, anyone who covers a lot of miles will enjoy those benefits and the diesel is likely to be the most economical option, over time, for those motorists who use their vehicles a lot.

How Accurate and Reliable Are Official MPG Figures?

The problem here is that fuel economy tests are not really representative of the way that people actually drive in the real-world. It would be fair to say that not many drivers ever drive in such a way as to match the standards required to meet the official figures. Careful and strict adherence to driving best practice would be a must if the optimum performance were to be achieved, with particular attention paid to keeping driving speeds within economical driving limits, along with the correct use of brakes, acceleration and other factors.

When deciding how to choose between a diesel and a petrol driven car, however, there are other considerations over and above the financial ones outlined above, to bear in mind.

Petrol Vs Diesel – Which Pype of Engine is Best For Which Type of Car?

The choice of petrol Vs diesel should not be made purely on the basis of MPG and fuel costs.

A diesel engine will develop more torque, and this makes them very suitable for certain types of vehicle, especially SUVs and four-wheel drive models where occasional off-roading will take place and rough terrain will be encountered.

On the other hand, those just looking for a small vehicle which is unlikely to go off road or be needed to carry heavy items may be better served by a cheaper petrol engine version of the vehicle they are considering buying. Those requiring a vehicle for work purposes and needing to use it for delivering goods, especially in remote areas, would be well advised to look closely at the diesel option.

Those looking for a sports car or other high-performance vehicle are unlikely to consider a diesel engine version, even if one is available, because the performance is never likely to be as good with acceleration and maximum speed on a diesel engine as it would be with a petrol driven option. It would be fair to say however that these performance differences have narrowed over recent years and a turbo driven diesel is nowadays quite capable of turning in a great performance.

So, How do They Differ in Performance?

Petrol engines have always been seen as being capable of delivering a smoother drive than a deisel with a more responsive performance, whilst diesels offer higher levels of torque (which equates to pulling power), making for a more relaxing drive, especially when coupled with an automatic gearbox.

It is fair to say that petrol engine vehicles need to be driven “hard” to give their best, so they naturally suit a ‘sportier’ style of driving coupled with a manual gearbox, if at all possible, to really get the best from that type of engine. Petrol engines are also better for smaller vehicles since they generally tend to be lighter and smaller and are therefore more suitable for today’s more compact vehicles designed for making short “hops” rather than longer journeys.

With the advent of the turbo charger it is quite reasonable to expect great performance from both types of engine but, if you are looking for pure acceleration and high-speed performance a petrol version is still likely to be your best bet.

Diesel Vs Petrol – The Environmental Argument

There is a bit of an urban myth surrounding petrol and diesel engines. Because of views formed back in the days when diesel was mainly used on commercial and agricultural vehicles, the general understanding was that the toxic emissions from a diesel engine vehicle were higher than petrol and that therefore diesel engines were less environmentally friendly.

In fact, modern diesel engines use more of a “lean-burn” technology which means that they typically use less fuel and more air in the process of powering the engine and by that method they can get close to the same level of performance as a petrol engine. It is true that whilst diesel fuel does contain a slightly higher level of carbon (2.68kg CO₂/litre) than does petrol (2.31kg CO₂/litre), the overall CO₂ emissions of a diesel engine vehicle tend to be that much lower.

In everyday use, as an average, the overall emission levels equate to around 200g CO₂/km for petrol engines and 120g CO₂/km in the case of diesel engines.

CO₂ however is not the only factor which determines the overall toxicity of an engine. CO₂, although not good, is not immediately harmful to humans whereas other toxic emissions from a motor vehicle engine certainly can be. Of these, perhaps the best known is Nitrogen Oxides, most often in the form of Nitrogen Dioxide, (NO₂), which is extremely toxic and Nitrous Oxide, (N₂O), more often referred to as a “greenhouse gas”. Another substance, Nitric Oxide, reacts with Oxygen and produces yet more Nitrous Oxide. Overall this makes for a toxic cocktail of unpleasant gases which are most certainly harmful to human beings and to the environment in general.

In the case of a petrol engine this problem can be significantly reduced by fitting a device known as a catalytic converter to the engine’s exhaust system. A catalytic converter will usually remove enough of these substances to mean that a petrol engine will emit around 30% less toxic gas than its diesel counterpart.

Sources:

  1. Do I choose petrol or diesel? – What Car
  2. Diesel vs Petrol Car: Which is Better? –  Auto Glass

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