Which car fuel?

What you need to know to make the right choice

Think carefully about the type of fuel you choose for your new car

Think carefully about the type of fuel you choose for your new car

If you're thinking about buying a new car then it's important to think carefully about the type of fuel – changes to emissions regulations and engine design mean that what was the right choice last time you changed your car may not be this time.

The European regulations that define exhaust emission limits for new cars (Euro 5 since 2009, and Euro 6) are becoming much more stringent, especially for diesel, in terms of reduction of particulate matter (tiny bits of soot) and oxides of nitrogen, both of which are blamed for causing breathing problems.

To meet these new regulations, car manufacturers have to fit extra emissions control equipment. This increases the cost of building the car, but can also makes it less suitable for certain types of use.

Diesel with DPF

We used to recommend a diesel engine for frequent short journeys as the engine works more efficiently earlier in the journey. Now though, the fitting of diesel particulate filters (DPF) means that diesel vehicles need regular long runs, some of which must be at high engine speed to clean (regenerate) the filter.

More about diesel particulate filters »

Lean burn petrol

Petrol engine emissions have to be reduced too.

Some manufacturers are adopting 'lean burn' in conjunction with direct injection fuel systems (the petrol is injected into the cylinders rather than being mixed with the air in the inlet manifold) to achieve improvements in fuel economy.

The higher temperatures at which these very lean mixtures burn results in more oxides of nitrogen so car manufacturers may have to fit nitrogen oxide (NOx) traps.

At high and mid-range engine speeds, these engines run very lean, using less fuel so direct injection engines are ideal for motorway runs, but much less suitable if the car is predominantly used in town.

At lower vehicle speeds the mixture returns to normal and cannot make use of the lean burn technology so there will be no fuel consumption advantage from this more complex and expensive system if most of your car use is for local trips.

Comparisons

  • Diesel cars usually cost more to buy, but generally have better resale values.
  • Petrol and diesel servicing costs are similar. Both require servicing, particularly an oil change, at least once a year.
  • Vehicle Excise Duty (Car tax) is based on CO2 emissions and diesel engines are more efficient so VED can be less.
  • Company cars still pay three per cent extra tax for a diesel car because its emissions are more toxic, but the lower CO2 emissions mean overall the company car tax should be lower.

If you cover a high mileage and the bulk of your driving is on motorways then a new diesel (with a DPF) is still a good option. If your driving is predominantly short journeys on local roads then a normal (not direct injection/lean burn) small petrol will be more suitable.

If you're buying a used diesel car first registered since around 2005 then check the specification carefully as it could be fitted with a DPF.

Biofuels

All road diesel and petrol now contain some biofuels – up to 5% ethanol in petrol (although this will soon increase to 10% in standard Unleaded and 5% in Super Unleaded) and up to 7% biodiesel in diesel.

You should not use a higher biofuel blend without checking with the vehicle manufacturer, that it's suitable for your car.

LPG

This is a by-product of crude oil extraction and the refining process.

LPG costs a little more than half the price of petrol or diesel, but fuel economy will be about 20-25% lower. Overall running an LPG car costs approximately a third less than a petrol only car – but only once you've recovered the cost of the conversion.

Conversion of an existing petrol car so it can run on petrol or LPG costs between £1500 and £2500, so you'll need to travel around 14,000 miles a year to make the conversion worthwhile.

LPG burns very cleanly and is an ideal fuel for town use, but remember you can't take an LPG powered car through Eurotunnel, even if the tank has been emptied or disconnected. There are also restrictions in some underground car parks here and in Europe.

Make sure the conversion is carried out by an approved installer.

UKLPG  Vehicle Register

UKLPG maintains a register of vehicles converted to run on LPG and only UKLPG Approved Autogas Installers can put vehicles onto the Register.  Your vehicle should be added to the Register as soon as the conversion is completed.

The Register is the only way for insurance companies, brokers, taxi licensing officers and the public to verify that a particular vehicle has been converted safely and meets the required standards.

An LPGA Approved Installer may inspect and, if found safe,  put any vehicle on the Register even if they have not converted it themselves.

If you have one of the old lpg conversion certificates and your vehicle does not appear on the Register, UKLP will add it on receipt of the old certificate.

London Congestion Charge

When the London Congestion Charge was introduced some LPG conversions qualified for an alternative fuels discount (AFD).

The AFD was closed to new applications in December 2010 and has been replaced by the Greener Vehicle Discount (GVD).

Only cars which emit 100g/km or less of CO2 and that meet the Euro 5 standard for air quality will qualify for the GVD.

More about the London Congestion Charge »

Hybrids

Several different hybrids are available which have a small petrol engine, an electric motor and a very large battery pack. During stop, start driving the battery is charged by the engine and a process called 'regenerative braking' which slows the car down by converting kinetic energy into stored electrical energy. With conventional braking systems the kinetic energy is wasted as heat in the brakes. For high speed motoring the battery/electric motor may assist the engine.

Hybrids are ideal for town driving, but if your driving is predominantly on a motorway then a diesel car might be a better bet for the best fuel economy.

Electric

With zero emissions in service, electric vehicles are ideal for use in towns and cities but their limited range and the need to plug in to recharge means that they will not be suitable for everyone.

If you're considering buying an electric car it's important to carry out an extended test drive so that you can be sure that range and charging needs suit your own lifestyle.

Read more about test driving an electric car »

(5 October 2012)

 

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