Six things you didn’t know about filling up your car with petrol

Carlton Boyce / 03 November 2015 ( 31 March 2017 )

How far can you drive with the fuel light on? Is it cheaper to fill up in the morning? We bust six myths about petrol and filling up your car.



Filling your car with petrol or diesel is a necessary evil and something we all do without a second thought. Which might be a mistake, because it can be a bit more complicated than you think…

Here are six things you might not know about filling up your car.

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1. How far can I drive with the fuel light on?

Every car has a reserve of fuel built in, so when your low fuel warning light comes on you don’t need to panic as you aren’t going to run out there and then.

In fact, the amount of fuel left in your car might surprise you – it certainly surprised us and spurred us on to produce this infographic

However, be warned: driving your car with only a small amount of fuel in the tank is not a good idea as you will be dragging sediment through your fuel system, which could result in a bill for hundreds, if not thousands, of pounds. 

Oh, and if you run out in some situations, like a motorway, for example, you risk being issued with a fixed penalty notice too…

Find out about other driving offences you can be penalised for...

Infographic to show how far you can drive with the fuel light on

2. What should I do if I put petrol in my diesel car by mistake?

More than 150,000 motorists put petrol in their diesel car by mistake every year, so you are in good company. Nor is it an expensive mistake, providing you immediately take the right action:

  • Do not turn on the ignition. Petrol acts as a solvent, weakening the lubricating effects of diesel and turning on the ignition starts the fuel pump, which circulates the petrol/diesel mix, causing catastrophic and expensive damage.

  • Ask for help to push your car away from the petrol pumps and into a safe place.

  • Call your breakdown service, which will take you to a garage to have your fuel tank pumped out.

Putting diesel in a petrol car is a less likely scenario, as the nozzle on a diesel pump is bigger than the one for petrol, making it almost impossible to put it into your car’s filler neck. However, if you do manage to put diesel in your petrol car, the advice is the same: don’t turn on the ignition and call your breakdown service.

Read our guide to what you should do if you break down

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3. Is it worth paying the extra for ‘premium’ fuel?

Most fuel retailers offer a premium petrol and diesel option and while the claims vary, most claim you’ll benefit from a cleaner engine and fuel system, more power, and/or reduced fuel consumption.

At a cost of around 10p a litre more than the standard fuel, the average motorist will pay around £5 more to fill their tank, adding around £100 a year to the average motorist’s fuel bill.

My experience is that it is worth it, especially if your car is old enough to need an MOT as the exhaust gases are generally cleaner, helping you pass the annual test.

So, if you are on a tight budget, the standard fuel will be fine but if you can afford it – or run a performance car – premium fuel does deliver what the retailers claim and is worth paying the extra for.

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4. How much petrol can I store at home?

The law says you can store up to 30 litres of petrol at home without registering with your local Petroleum Enforcement Authority. However, you must not exceed the following:

  • A maximum of 10 litres in a single plastic container; or

  • A maximum of 20 litres in a metal container.

In any case, you must store them in an approved container and in a well-ventilated area, preferably well away from the house; your garden shed or garage is ideal. It cannot be stored in any living accommodation, ie, inside your house.

The law also allows you to carry up to 30 litres inside your car in an approved container, but I wouldn’t recommend carrying any more than five litres at a time: remember, petrol is such a powerful explosive that it is capable of propelling a couple of tonnes of metal over a distance of more than 30 miles…

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5. Is supermarket petrol bad for my car’s engine?

No. Generally speaking, petrol is petrol and diesel is diesel and I’d be much more worried about filling up with stale fuel from a small village garage than a discounted supermarket that turns over a lot of fuel, ensuring a constant and fresh supply.

However, if you are worried – and there have been cases of poor quality fuel causing problems in the past – just tuck your petrol receipts in the glovebox and if you ever do have a fuel-related problem, you’ve got the evidence to hand to support your claim for damages.

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6. Are there any tips you can give me on buying fuel at a petrol station?

Yes, lots! Here are some of my favourites:

  • If you see a petrol tanker filling up the underground tanks of a petrol station, don’t buy fuel there for a few hours. Pumping fuel into the tanks stirs up the sediment that lies at the bottom of even the cleanest one. It will then be pumped into your car’s fuel tank and then into your engine.

  • The density of petrol varies according to the temperature, so it makes sense to buy petrol in the cool of a summer’s morning, when you’ll get more bang for your buck.

  • Don’t pump petrol or diesel into your tank at the fastest rate you can, as this will churn the fuel up. Pumping slowly ensures you get 100% liquid, not a mixture of fuel and fuel vapour.

  • Use a price comparison service to find the cheapest fuel in your area, but the best way to reduce your fuel costs is to drive more economically.

For more useful hints and tips, visit our motoring section.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.