When you are shopping for a new car, one of the first decisions you will need to make is whether you want a diesel or petrol engine. These days, most car manufacturers offer both for the same model.


Last week, the Government warned drivers to “have a long, hard think” before purchasing a diesel car to try and eliminate air pollution, especially for those that drive in urban areas, and encouraged them to opt for “the least polluting vehicle they can”.


My Car Credit realise this warning could create confusion for drivers who are researching buying their next new car and have weighed up some of the pros and cons of diesel versus petrol engines. With decisions like this to make, it is important to consider practicalities rather than just personal preference.


The cost of the car


Generally, diesel cars tend to cost more than petrol cars. Some car manufacturers can charge up to £1000 – £2000 extra for the same model – just because it has a diesel engine. Diesel cars do however have a reputation of lasting and running for longer.


Diesel cars also generally depreciate at a lower rate (the biggest cost in car ownership) so this is important to consider when deciding whether a petrol or diesel car will be more cost effective overall.


Fuel economy and ongoing costs


Where fuel economy is one of the most important factors, diesel cars have long been considered the best choice for car buyers. However, with diesel emissions currently under scrutiny, car manufacturers demanding premiums for diesel models and petrol engines becoming more economical, is diesel really the answer to lower cost motoring?


Experts would argue motorists travelling less than 10,000 miles per year and more prone to shorter trips and city driving would be better off with a petrol engine. Diesel engines tend to work best for longer journeys and motorway style travelling.


It is also important to consider that a petrol car might deliver up to 30% less fuel economy than a diesel car but the running costs may be less if you keep the car for longer than three years.


We take this example from Driving Test Tips:


Popular mid–sized car, the Ford Focus 1.6 diesel does nearly 20mpg more than its 1.6 petrol equivalent, but its purchase price is £1090 higher.


Based on 10,000 miles per year and with Diesel prices at 141.44p per litre and Petrol prices at 135.96p per litre, the fuel expenses of the petrol version in the first year would generate a saving of £334.95 and the diesel driver £755.05 out of pocket.


After 3 years of driving the diesel car at 10,000 miles per year, the diesel driver will have saved £1,004.84 in fuel expenses compared to the petrol driver. The diesel car, however, cost £1090 more to buy initially so in effect the diesel driver has almost broken even.


The cost of diesel may also increase in relation to tax fuel. Diesel contains approximately 10% more energy than petrol.




Typically diesel cars tend to cost on average 10-15% more to insure than petrol cars.


The two main reasons for this are that 1) diesel cars can often be more expensive to repair due to the complexity of their engines and, 2) the overall replacement costs would be higher for a diesel car if it was stolen.


Servicing Costs


The difference between servicing costs for diesel and petrol cars is usually quite small. Diesel cars need to be serviced less than petrol cars but if they do need any repair work, it’s usually more expensive. However, due to advances in petrol engine technology, petrol cars are getting more reliable, so the need for repairs is becoming much less.


Still unsure? Why not access this handy Fuel Cost Calculator from nextgreencar.com. You can calculate and compare the costs per mile weekly and monthly and also annual fuel costs for both diesel and petrol cars.