What Really Happens When You Run Out Of Fuel

Running out of fuel is more than just an inconvenience it can be harmful to your vehicle and potentially dangerous, particularly if it happens on a busy road or motorway. Whether your car runs on petrol or diesel, letting the tank run dry can lead to costly mechanical issues.

At Bartlett Automotive, we regularly advise drivers across Bedfordshire, Hertfordshire, and Buckinghamshire on vehicle safety and maintenance and this is a topic that catches many motorists off guard.

What Happens Before the Tank Hits Empty?

Even before your fuel gauge hits zero, problems may begin. The bottom of your fuel tank can contain small amounts of sediment or debris, particularly in older vehicles. When your fuel level is low, the fuel pump may draw in this contaminated fuel, which can:

• Clog the fuel filter
• Damage fuel injectors
• Harm engine components due to improper fuel flow

While the risk for modern cars is lower with plastic tanks (which don’t rust) and improved filtration/fuel pump design. The main risk is the fuel pump overheating and failure due to a lack of cooling/lubrication when uncovered by fuel, they’re not designed to cope with long-term exposure to sludge or deposits.

“E” Light vs. Actual Empty (Range Anxiety):

• Recommendation: Mention that the “E” light typically comes on with 40-50 miles of range remaining. Emphasise that this is a buffer, but relying on it is risky because the fuel remaining is an estimate based on recent driving, and things like hill climbs or spirited driving can quickly reduce the actual distance.

Diesel Engines: Why Running Dry Is Worse

Diesel systems are especially sensitive to running out of fuel. That’s because diesel fuel acts as a lubricant for the fuel pump and injectors. When a diesel engine runs dry, air enters the system, causing:

• Fuel pump wear due to lack of lubrication
• Injector damage
• Potential engine misfiring or stalling

In most cases, a diesel system will need bleeding before it can restart, to remove air pockets from the fuel lines, which typically requires a trained technician.  Do not continually try to start the engine as this can cause further damage.  Modern common diesels with electric lift pumps (in the tank) are often designed to be “self-priming” (or self-bleeding) after a few ignition cycles, but this is not guaranteed and still puts significant strain on the system and professional assistance is often still needed to be safe and avoid damaging the high-pressure pump.  Older diesels nearly always require manual bleeding.

Petrol Engines: Slightly More Forgiving, But Still Risky

Petrol engines are generally more tolerant of low fuel levels because they’re designed to operate with a mix of air and fuel. That said, if you run out entirely:

• The fuel pump may draw in air, which can lead to overheating and eventual failure
• Sediment at the bottom of the tank may still cause filter or injector blockages

You might be able to simply top up with petrol and start the engine again, but repeated instances increase wear and tear and could eventually lead to expensive repairs.

What Should You Do If You Run Out of Fuel?

If you do find yourself running critically low or completely out of fuel, follow these steps:

1. Pull over safely as soon as possible, ideally in a lay-by or quiet road. Turn on your hazard lights.
2. Avoid the hard shoulder unless it is a genuine emergency stopping on a motorway hard shoulder is extremely dangerous and should only be done as a last resort.  If on a Smart Motorway where there is no hard shoulder, if possible try to coast to an Emergency Refuge Area (ERA)
3. Call for assistance — either a breakdown recovery service, or a friend/family member who can bring you fuel. If on a motorway and you must stop in a live lane, turn on your hazard lights, and if safe to do so, follow the instruction to exit the vehicle via the passenger side and wait behind the barrier.  Crucially call 999 immediately (or use the SOS button) to alert National Highways. If your vehicle is diesel-powered, you may need professional help to restart it.
4. Stay inside the vehicle if you’re on a fast road and it’s unsafe to exit wait for professional help.

It is technically not illegal to run out of fuel on a UK motorway, as the law allows for stopping on the hard shoulder due to “lack of fuel.” However, you can be prosecuted for “careless driving” if it’s determined you entered the motorway knowing you had insufficient fuel and caused a danger (e.g., sudden stopping, obstructing traffic).

Pack an Emergency Kit

We recommend keeping an emergency kit in your car at all times. Items such as reflective warning triangles, a high-vis jacket, lights, a small high quality UK approved fuel container, a fully charged power bank for a mobile phone and a first-aid kit can make a major difference if you break down in a vulnerable spot.
See our full guide to essential emergency kits here

Carrying Spare Fuel: What the Law Says

It is legal to carry spare petrol or diesel in your vehicle, but only in approved fuel containers. According to the Health and Safety Executive (HSE):

• HSE guidelines for filling up at a forecourt: You may fill a maximum of two approved portable fuel containers with a total capacity not exceeding 30 litres.
• Containers must be purpose-built, securely sealed, and clearly labelled
• Never store fuel inside the passenger compartment always use the boot or a secure external storage area

Improper storage could pose a fire risk and may be considered an offence, especially if containers aren’t compliant with UK regulations. 10L plastic/20L metal is the max size per container in or near a domestic dwelling!

What About Electric Vehicles?

As more drivers make the switch to electric vehicles (EVs), it’s important to understand how running out of charge differs.

Unlike petrol or diesel cars, EVs cannot be topped up roadside unless mobile charging equipment is available and this is still limited in many areas. Running out of battery power typically means:

• The vehicle must be recovered by a breakdown service
• It may require towing to the nearest charging point
• Some recovery providers now offer mobile charging units, but these are not yet widespread

Most EVs go into a “limp mode” well before the battery is fully depleted (usually showing 0% or ‘turtle mode’). This allows a very slow, short-distance drive to a safer stopping point (e.g., off a busy road) rather than an instant stop like a fuel car.

Planning ahead is essential for EV drivers — especially on longer trips — and understanding where your nearest public charge points are can help avoid getting stranded.

Final Thought from Bartlett Automotive

Keeping an eye on your fuel or battery level may sound obvious, but it’s one of the easiest and most effective ways to avoid breakdowns and costly repairs.

If you’ve recently run your tank dry, or suspect your vehicle’s fuel system may have been affected, we recommend booking in for a quick check-up at Bartlett Automotive to prevent long-term damage.