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Petrol vs Diesel - The Great Debate

Diesel cars have soared in popularity over the decade, as drivers are tempted by their better fuel economy but with the closing gap on fuel costs, the issues with diesel particulate filters and the increased focus by manufacturers on improving the fuel economy of their petrol engines, it is important to continually assess which fuel is best for YOU, diesel or petrol?


Fuel Economy  

Over previous years, comparing manufacturers fuel economies on paper, diesel engines have been around nearly 30% more fuel efficient than their petrol counterparts.

However manufacturers have started developing a range of fuel efficient manual petrol engines, with the Ford leading the field with their 1.0 litre Ecoboost engine. It is 20% more fuel efficient than its older petrol counterpart but the latest diesel engine is still at least 16% more efficient.

For example, comparing fuel economies for the Ford Fiesta:

In reality as an instructor with ‘real life’ driving especially with pupils in the vehicle you never achieve the manufacturers’ fuel economies that are achieved in test conditions, however they are great for comparisons against your actual fuel spend to roughly what fuel savings you are likely to achieve:

New engine (MPG) / Current engine (MPG) * 100% = Fuel efficiency gain
Fuel Spend (£) * Fuel efficiency gain = Cost saving

Obviously the greatest cost saving is gained by those doing the greatest mileage, but even low mileage users can benefit from savings aswell.  

But be careful as petrol engines do tend to heat up much quicker than a diesel vehicle and therefore becomes more effective more quickly, so if you are doing short runs a turbo petrol can make sense.

Alternative fuel vehicles

The petrol electric hybrids have led the growth of so-called alternative fuel vehicles in the past few years, despite the recent introduction of the diesel-electric hybrid.

There are two factors that have resulted in shrinking premium for hybrid over conventional diesel-engines cars; it has become more expensive to engineer new diesel engines to meet current and future emissions regulations and the increase in demand for petrol-electric hybrid models and improvements in technology has helped to drive down the cost of components associated with the hybrid drive system.  The energy capturing function of a hybrid car, which flees like strong engine braking, reduced wear on brake pads and prolongs their life.

Fuel costs   

In the UK fuel pricing favours petrol, with diesel being around 10% more expensive than petrol per litre. 

Compare your local prices at Petrol Prices (

Diesel Participate Filters (DPFs)

Due to changes to European Legislation (Euro V) to help reduce C02 emissions, Diesel Particulate Filters (or DPFs) have been introduced to modern diesel engines.  This device is designed to remove diesel particulate matter (soot) from the exhaust gas of a diesel engine.  

Diesel cars tend to have lower emissionsThey work by trapping soot and harmful particulates in the exhaust, reducing emission by up to 80 per cent. This benefits the environment, as well as reducing the owners’ car tax. However if the vehicle is not ‘allowed to re-generate’ by the drivers driving style, particularly for driving instructors and the stop-start nature of their business this result in additional bills.

In addition, dependent on the manufacturer the DPF will need to be replaced, but this will vary according to how the vehicle has been driven. 
In order to meet the next set of European Legislation, Euro6, diesel engines will increasingly need exhaust after-treatment, which includes costly particulate filters and could also need a reservoir containing a chemical such as ‘Adblue’ that may need replenishing during or even in between services.  The deadline to manufacturers is currently mid 2015, but this is already in place on some models.

Other factors to consider

Diesel engines tend to offer increased torque (pulling power) from lower revs, which is especially useful when towing or overtaking.  In addition diesels are harder to stall, though each instructor has their own view on whether this is a bad or good thing.
Insurance costs can vary by model and can favour either option, so check before you buy.

So Petrol v Diesel ... the choice is yours

Clara Gibson, General Manager at CA cars commented “Our experience is that diesel is still perceived as the preferred fuel type, but we are continually reviewing advancements in technologies with manufacturers and reviewing this assumption. This enables us to give our customers a range of cost-effective vehicles with the relevant information relating to fuel economy and other issues so that they can make an informed choice. With emerging technologies and new types of petrol vehicles with their better fuel economy, coupled with the increasing legislation around a diesel engine over the next few years we will continue to introduce this new breed of petrol engines to our contract hire range. So watch this space as other manufacturers are due to launch their new petrol products starting from this summer.


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