What Type and Grade of Gasoline Should You Use?

The car’s handbook, and sometimes a label near the fuel filler, says what type and grade of fuel you should use.


Most petrol cars on the road now run on unleaded fuel and those with catalytic converters can only be run on it. Petrol with a lead substitute is still available on some forecourts for old cars which still need the additive to protect the engine’s valve seats. Petrol has an octane number which signifies its grade, but in the UK is labelled Premium for 95 octane and Super for 98 octane. Most cars run on Premium and there is no point using a higher grade of petrol than your car requires because it does not improve performance. A few high performance cars do only give their maximum performance on Super, but these days most will also run on Premium and few drivers are likely to notice the difference.


Bioethanol is a petrol alternative made from vegetable sources. If your car is capable of running on bioethanol, it will also run or petrol or any mix of the two. However, you can’t use bioethanol in a petrol engine not adapted for it. Bioethanol cars therefore only need one fuel tank where dual-fuel cars have a conventional petrol tank plus an entirely separate one, with a special filler connection, for liquid petroleum gas.


Diesel has a cetane number but you don’t need to know it because oil companies supply diesel with a higher cetane rating in the winter for easier running and to reduce the risk of ‘waxing’, where a wax-like substance forms in the oil at very low temperatures, clogging the system. However, it is worth seeking out low sulphur diesel fuels because they make the car run smoother and cleaner.

Increasingly, you will see diesel advertised as ‘bio-diesel mix’ where conventional diesel, derived from the same crude oil as petrol, is mixed with diesel obtained from vegetable sources, like oilseed rape. Diesel that is up to five per cent bio-fuel can be used in any diesel engine. It is low in sulphur and other impurities so, as well as making the exhaust cleaner, it seems to make diesels run smoother and, in many cars, results in a slight improvement in fuel consumption.

We shall also be seeing pure bio-diesel more widely available with, hopefully, a considerable tax advantage because it is from renewable sources. However, pure bio-diesel cannot be used in all engines so you must check in the handbook or with your car’s manufacturer to see if it is safe to use it.

Incidentally, don’t be tempted to use tax-free oils like heating oil, vegetable oil or ‘pink’ agricultural diesel in your diesel car. To do so is illegal and though your diesel may run on them, heating and vegetable oil do not have the right additives to protect the engine and agricultural diesel dyes the fuel filter and pipes pink so the authorities can see you’ve used it.

Getting it wrong

The AA alone has around 100,000 calls a year to drivers who have put petrol into a diesel car. You shouldn’t be able to do it the other way round, unless you have a very old car, because diesel pumps have a larger nozzle than unleaded petrol pumps. On old diesels you could get away with mixing a few litres of petrol with diesel as long as you topped up with diesel as soon as possible. But modern diesels’ fuel injection operates at very high pressures using high speed fuel pumps and all this needs the full lubricating qualities of the oil which is diluted by petrol. So with a modern diesel, do not start it if you make this mistake: call your breakdown service because a wrecked fuel pump is extremely expensive to replace and warranties do not cover damage resulting from using the wrong fuel.

Related posts:

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  2. 2011 Volvo V60 Price
  3. How Does a Diesel Pump Work?
  4. Honda Civic Type R MUGEN 2.2
  5. A Guide to Green Car Fuel Types

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