Do you play fuel station roulette? All about when the low fuel light is on

Most people have driven around with the low fuel light or low battery alert on. Some people even play fuel station roulette on a regular basis, driving as far as they dare with the warning light on and their car running on the dregs of its fuel or battery. But do you really know how many miles your car has left in it when the warning light comes on?

What is your car’s fuel light range?

That’s like asking how long a piece of string is. It depends on how the fuel gauge is calibrated. On some cars, the gauge will tell you the tank is empty with zero range when it’s still got around a gallon left in it. On others, the opposite is true. We’ve heard tales of drivers whose cars have stopped running despite the read-out saying they’ve still got a range of 30 miles. 

And the range varies wildly between different models, manufacturers and even whether your car is petrol, diesel or electric.

How accurate are fuel gauges?

This varies greatly, too. Some aren’t very accurate at all, some are; many err on the side of caution. Some modern cars have a range function on their computer. When the fuel or low battery light comes on, the range function will probably pop up to say how many miles you have left in the tank. However, this is usually an average figure gleaned from your overall miles per gallon up to that point. If you’re on a motorway where you’re typically driving quickly, your car will use fuel or battery at a faster rate

Is there really a reserve fuel tank?

Some people think cars have a second ‘reserve’ fuel tank. They don’t. When the fuel light comes on, the fuel is running out.. However, when the fuel light comes on does vary. On some cars it will be when the tank has 15 per cent of its fuel remaining. On others it will be at less than 10 per cent. Check your car’s user manual to find out what your reserve fuel is.

Electric vehicle batteries appear to maintain a reserve, meaning the car can continue driving for up to 20 miles even after the onboard computer displays 0%. This reserve range varies by model. Manufacturers often include this buffer to help drivers avoid getting stranded before the car shuts down.

Our advice though? Don't risk it!

How many people run out of fuel every year?

Around 4.6 million people a year run out of fuel or battery. That’s one in seven motorists. And 10.3 million motorists let their tank get as close to empty as they dare before refuelling. On top of the roadside not being a safe place to spend time, running out of fuel can be bad for many reasons. It could cause potential damage to the fuel pump or the accumulation of debris making its way into the engine - both of which can cost you heartache, time and money in the long run.

What to do when the fuel light comes on

Drivers should view the fuel or battery light as a final warning and head to the nearest fuel or charging station. You can’t be certain how much fuel or battery you have left, so take action. Try to use the accelerator sparingly and attempt to maintain momentum where it’s safe to do so. Your car’s most economical speed depends on the kind of engine it has and its gearing.

But generally, the lower the revs and the less the accelerator is used, the more mileage you’ll get. If you want to make tiny gains in mileage, keep windows up at higher speeds and turn the air-conditioning off. 

Is it harmful to run your car with low fuel?

Petrol and diesel cars

Cars are clever but they can’t defy the laws of physics. Car manufacturer SEAT says it’s perfectly reasonable to expect a car that’s running low on fuel to misfire or for the engine to stutter, particularly on gradients. This is because the fuel pump can’t pick up the dregs of fuel in the tank. Running a car dry can also cause unburnt fuel to enter the exhaust system. This might be harmful to the catalytic converter in petrol cars or the particulate filter in diesel cars. Both are very expensive components to replace.

Modern fuel injection cars use an electric fuel pump which sits in the fuel tank. This is so it can use the fuel as a coolant. Run the car out of fuel and the fuel pump will start to get hot. Experts say this should only result in damage if the car is run persistently with a very low fuel level.

Electric cars

Driving an electric vehicle with a low battery can negatively impact its battery health and potentially affect its performance. While it's generally safe to drive an EV with a low battery, it’s recommended that the ‘sweet spot’ for battery health and lifespan is between 20% to 80%. Electric vehicle drivers should always make sure their car has enough battery life to reach their destination.