When an unexpected shortage hits the fuel pumps or a generator runs dry at the worst possible moment, many people start to wonder whether kerosene could serve as a temporary substitute for diesel. It’s a common question in rural parts of the UK, especially in communities where both fuels are kept on-site for heating and machinery. While the idea sounds like a practical workaround, the reality is more complicated.

With over two decades of experience in researching and writing about fuels, engines, and safety regulations, I’ll walk you through everything you need to know—including whether it’s safe, legal, or financially sensible to pour kerosene into a diesel engine, even “just this once.”

What Are the Key Differences Between Diesel and Kerosene?

To understand whether kerosene can replace diesel, it’s essential to know what sets them apart.

1. Composition and Refining

Diesel is a heavier fuel with higher lubricity, which helps keep fuel pumps and injectors working smoothly. Kerosene—used commonly as heating oil (Kerosene 28) and even for aviation fuel—is lighter, cleaner burning, and less oily.

2. Flash Point

Diesel has a higher flash point, meaning it is less flammable and safer to handle and store. Kerosene’s lower flash point makes it ignite more easily, which affects how engines handle combustion.

3. Lubrication

This is one of the biggest issues. Diesel engines rely heavily on lubricity within the fuel to protect high-pressure injection components. Kerosene lacks this lubrication, increasing wear and tear.

4. UK Tax and Regulations

The UK has strict rules regarding fuel use, and using non-approved fuels in road vehicles can lead to hefty penalties. Even if the vehicle runs perfectly, the legal consequences alone can outweigh any emergency benefits.

Can Kerosene Be Used in a Diesel Engine in an Emergency?

Short Answer:

It should be avoided unless you have absolutely no alternative, and even then, it is risky, may cause damage, and may be illegal depending on the circumstances.

Let’s break this down further for clarity.

Mechanical Risks: What Happens Inside the Engine?

1. Lack of Lubricity Can Cause Major Damage

Modern diesel engines—especially common-rail and high-pressure systems—depend on diesel’s lubricating properties. Running kerosene can cause:

  • Premature wear of fuel pump components

  • Injector failure

  • Reduced fuel system life

This damage might not happen instantly, but even a few hours of use can accelerate wear in ways that lead to costly repairs later.

2. Higher Combustion Temperatures

Kerosene burns hotter and cleaner. While that may sound positive, the increased combustion temperature can stress engine components not built for that heat profile.

3. Reduced Power Output

Because kerosene has lower energy content than diesel, the engine may:

  • Lose power

  • Run rough

  • Struggle under load

This is especially problematic if the emergency involves towing, farm work, or powering essential generators.

Is It Legal to Use Kerosene in a Diesel Vehicle in the UK?

For Road Vehicles:

It is illegal to use heating kerosene (Kerosene 28) as road fuel. HMRC considers this rebated fuel, and using it in a vehicle intended for public roads constitutes fuel duty fraud.

Penalties can include:

  • Fines

  • Vehicle seizure

  • Back-dated duty fees

Even in a genuine emergency, the law does not allow the substitution.

For Generators, Agricultural Machinery, and Off-Road Equipment:

Here's where things get more nuanced. Following the 2022 UK red diesel rule changes, only specific industries can legally use rebated fuels. Using kerosene for off-road diesel engines may still fall foul of regulation depending on the equipment type.

In short, legality depends on what the engine is powering—and in most cases, it’s still not permitted.

Will the Engine Start and Run on Kerosene?

Technically, many older diesel engines may run on kerosene—particularly pre-2000 designs with simple mechanical injection pumps. This is partly why kerosene was historically mixed with diesel in colder climates to prevent gelling.

However, today’s engines are far more precise and far less tolerant of poor lubrication or low-viscosity fuels. Your modern car, van, or diesel generator is far more likely to suffer damage than benefit from such improvisation.

Safe Emergency Alternatives You Should Consider Instead

If you ever find yourself without diesel, here are safer and more reliable options:

1. Keep a Backup Supply of Diesel

Legally stored diesel can last 6–12 months, or longer with stabilisers.

2. Use Emergency Diesel From Approved Containers

Many businesses and farms keep emergency reserves specifically for power outages and essential equipment.

3. Call a Mobile Fuel Delivery Service

Across the UK, several services deliver diesel to vehicles, farms, and generators 24/7.

4. If Using a Generator: Switch to a Battery Backup

A UPS or solar-battery system can provide power long enough to safely refuel.

What About Mixing Diesel and Kerosene?

Some people consider blending rather than using 100% kerosene. While a diesel-kerosene mix was once used to improve winter performance, this practice is not recommended for modern UK vehicles.

Even a small quantity can:

  • Reduce lubricity

  • Void manufacturer warranties

  • Increase engine wear

And again, legal issues still apply.

Final Verdict: Should You Do It?

For UK drivers:

Do not use kerosene in place of diesel—mechanically, legally, and financially, it’s not worth the risk.

For off-road machinery:

Even in emergencies, it is still risky and often illegal. Check your industry’s specific fuel allowances before even considering it.

For generators:

Some older models may tolerate kerosene better, but it still increases wear and may void warranties.

Conclusion

While kerosene and diesel may seem similar, their differences are significant enough to make kerosene an unsafe and often unlawful substitute in the UK. The risks—engine damage, safety hazards, and legal penalties—far outweigh any short-term convenience.

In a real emergency, it’s far better to rely on approved diesel supplies, delivery services, or alternative power solutions. Kerosene should remain where it belongs: in heating systems, aviation, and other applications specifically designed for it—not inside your diesel engine.