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Can you run your car on cooking oil?

  • Is cooking oil really a suitable alternative to regular fuel?
  • Find out if it's cheaper to make your own biodiesel
  • Parkers weighs up the pros and cons

Written by Graham King Published: 19 April 2022 Updated: 18 January 2024

Is vegetable oil a suitable alternative fuel, given the high price of petrol and diesel? As leftfield as the question may seem, it’s fair to ponder at a time when drivers are considering every option to relieve the pressure on strained household budgets. While some are prepared to simply drive less and walk more, ride a bike or use public transport, others might be considering switching to an electric car or fuelling their car with cooking oil.

When fuel prices rocketed in early 2022, a video of one driver filling his fuel tank with cooking oil went viral, sparking a lot of interest in the concept. Here, we look into the viability of using Hydrogenated Vegetable Oil (HVO) and Waste Vegetable Oil (WVO), how it affects your car and the costs involved.

Can you use cooking oil in modern cars?

The first thing to note is that cooking oil cannot be used in petrol engines. It’s too viscous (thick) to ignite when a spark plug fires, in the way petrol does. What’s more, it can clog fuel lines and confuses the sensors that gauge how much fuel to send to the engine’s cylinders. So, if you drive a petrol car and you’re looking at alternatives, consider switching to an electric car, maybe car share or (insert side hustle of choice).

If you run a diesel car, though, you may be thinking ‘Right then, let’s go grab some sunflower oil.’ But hold on because it’s not quite that simple.

The high viscosity of cooking oil means it can clog the ultra-high pressure fuel injectors modern diesels use, and there’s still the problem of it confusing fuel metering sensors. As a result, there’s a school of thought that cooking oil is best left for much older diesels with low-pressure injection and few electronics. But, even in those cars, cooking oil can still clog up the fuel filter and lines, causing other problems and expenses further down the line. Cooking oil also doesn’t burn as completely as diesel, so the engine won’t run as smoothly. The car will also smell vaguely of chips.

There are, however, ways of getting around the problems of using cooking oil to fuel a modern diesel car.

Mazda CX-60 - Can you run your car on cooking oil?
Sophisticated modern diesels like the Mazda CX-60 don’t take kindly to cooking oil.

Modifying vegetable oil for use in cars

Firstly, you can change your cooking oil. But don’t go tipping the waste oil from last night’s dinner into your car’s fuel tank (we’ll come onto that). We mean the clean, unused HVO available from the supermarket.

Modifying the oil means adding regular diesel to it. That thins the oil, reducing the rate at which the fuel system will eventually clog. The oil also burns better so the engine runs more smoothly. Modifying the oil doesn’t eliminate the problems it can cause, but it does increase the time between trips to the garage.

Converting your diesel engine 

As we’ve established, fuelling your car with cooking oil presents some problems. But you can modify your car to get around them.

First thing that’s needed is another fuel tank for the oil. Having separate tanks allows you to choose whether oil or diesel is used at any moment, though the car will always start on diesel. The oil tank is heated to reduce viscosity, so it’ll flow through the fuel lines and atomise into the cylinders more efficiently.

On top of that, the engine needs new fuel injector nozzles with better filtration, specially designed glow plugs and new coolant lines. Add all that up and you’re looking at around £2,000 for a full conversion.

There are actually a few vehicles that run on HVO available to buy brand-new. But, as they’re Mercedes Unimog off-road trucks, they’re not exactly practical family transport!

Mercedes Unimog - Can you run your car on cooking oil?
Mercedes Unimog is the only factory-spec vehicle able to use HVO.

Do I need clean cooking oil to fuel my car?

You can’t just tip cooking oil straight from the pan into your car’s fuel tank. It’s full of food particles and fats that will clog the engine in very short order. You can filter oil by straining it through fine fabric, but that’s fiddly and messy. Besides, a single domestic kitchen is highly unlikely to generate enough WVO to fill a fuel tank.

WVO filtration is big business, though, worth almost £6 billion globally in 2019. Big-name oil suppliers like Oileco and Cator Oils buy WVO primarily from commercial kitchens and other sources which generate over 100,000 tonnes of the stuff annually in the UK alone. The WVO is filtered several times to make it clean enough to use as fuel. McDonald’s famously runs its fleet of commercial vehicles on WVO collected from its restaurants’ fryers.

Filtered WVO is generally only available to commercial vehicle fleets. It may take some time to find a supplier who’ll sell you some to run your car on, and you might have to buy in bulk. But there could be an enterprising local chip shop that filters and sells its own WVO.

WVO filtration plant - Can you run your car on cooking oil?
WVO filtration is big business.

What’s the difference between vegetable oil and biodiesel?

Biodiesel is essentially vegetable oil with the glycerine removed – that’s the stuff that makes oil thick and gloopy. However, there are many standards biodiesel must meet for it to be sold as such, which cooking oil doesn’t.

According to Oileco, one of the biggest WVO refiners in the UK, biodiesel burns 88% cleaner than regular diesel. Biodiesel is a good way of reducing your carbon footprint, then, but it’s not without environmental issues. Planting crops for biofuel can reduce biodiversity and divert agricultural capacity from the food chain.

Is is cheaper to use cooking oil in my car?

Until early 2022, 80% of sunflower oil sold in the UK was sourced from Ukraine. Since the country was invaded by Russia, the price of all cooking oils has spiked. At the time of writing, one litre of supermarket own-brand vegetable oil costs an average of 188.6p. By contrast, diesel costs 147.6p on average. The maths aren’t in oil’s favour.

You could buy in bulk from a cash-and-carry or Amazon. You can also find WVO sellers on Facebook Marketplace and eBay, though it’ll probably need filtering which leaves a lot less oil than you started with.

Once you factor in the cost of converting your car’s engine to run on vegetable oil and any filtration equipment you need, it starts to look quite expensive. Unless you can find a friendly local chippy selling cheap, filtered WVO, it’s best to stick with the black pump.

Vegetable oil bottles - Can you run your car on cooking oil?
Using HVO as fuel makes more financial sense if you buy in bulk.