Can Your Car Run on Cooking Oil? The UK Guide

With petrol and diesel prices remaining stubbornly high across the UK, many motorists are understandably seeking out cheaper alternatives to keep their vehicles on the road. The ongoing cost of living crisis and sky-rocketing fuel prices are putting immense pressure on household budgets, making the idea of unconventional fuels increasingly appealing. While some drivers opt for reducing their journeys, embracing walking, cycling, or public transport, others might be considering the intriguing possibility of running their car on cooking oil, or perhaps making the switch to an electric vehicle to mitigate the expense of filling up.

The concept of powering a car with cooking oil isn't entirely new, but the dramatic surge in fuel costs over recent years has certainly reignited interest in this unconventional idea. This renewed curiosity was significantly bolstered by a viral video in 2022, which showed a driver seemingly filling their fuel tank with cooking oil. In this comprehensive guide, we'll explore everything you need to know about potentially running your car on Hydrogenated Vegetable Oil (HVO), how it compares to Waste Vegetable Oil (WVO), and whether attempting to fuel your vehicle with cooking oil or even making your own biodiesel is a genuinely viable alternative for the average British motorist.

Can Modern Cars Really Use Cooking Oil?

The first crucial point to understand is that cooking oil is absolutely unsuitable for use in petrol engines. Its fundamental properties simply do not align with the requirements of a petrol combustion system. The primary issue lies in its exceptionally heavy viscosity, making it far too thick to be atomised and ignited effectively by a spark plug, which is how petrol engines operate. Furthermore, this thickness can lead to severe blockages within the delicate fuel pump and fuel lines, causing significant mechanical distress. Beyond physical blockages, cooking oil can also confuse the sophisticated electronic sensors that meticulously regulate the precise amount of fuel required for optimal engine performance, leading to ignition problems and erratic running.

Therefore, if you drive a petrol car and are looking for ways to reduce your running costs, directly using cooking oil is not an option. Your best bet would be to consider switching to a more economical petrol model, exploring the benefits of an electric car, or utilising one of the many car-sharing services now available.

For those driving a diesel car, the thought might cross your mind: 'Right then, time to grab some sunflower oil!' However, it's not quite as straightforward as that. Modern diesel engines, particularly those found in vehicles produced in recent decades, utilise ultra-high pressure fuel injectors designed for the much thinner consistency of diesel fuel. The heavy viscosity of cooking oil can quickly clog these precision components, leading to costly damage. The problem of confusing fuel metering sensors also persists in diesel engines, potentially disrupting the delicate balance required for smooth operation. Consequently, there's a prevailing school of thought that cooking oil might only be marginally better suited for much older diesel vehicles, which typically feature lower-pressure injection systems and fewer complex electronics. Even in these older models, however, cooking oil can still cause blockages in the fuel filter and lines, leading to unforeseen problems and expenses further down the line. Another notable drawback is that cooking oil does not burn as completely as diesel, resulting in a less efficient combustion process and a noticeably less smooth-running engine. And, of course, there's the distinct and often amusing side effect: your car will likely emit a faint, yet unmistakable, aroma of chips!

Despite these significant challenges, there are certain methods and modifications that can, to some extent, mitigate the problems associated with using cooking oil to fuel a modern diesel car.

Modifying Cooking Oil for Vehicle Use

While the idea of simply pouring the waste oil from last night's fish and chips into your car's fuel tank is ill-advised (more on that later), it is indeed possible to modify clean, unused cooking oil, such as HVO available from supermarkets, to make it more suitable for vehicle use. The key to this modification is to blend the cooking oil with regular diesel fuel. This process effectively thins the cooking oil, significantly reducing its viscosity. By making it less thick, you decrease the rate at which the fuel system components, such as filters and lines, will eventually clog. Moreover, this blending improves the combustion properties of the oil, allowing the engine to run more smoothly and efficiently. While modifying the oil in this manner doesn't entirely eliminate the potential problems it can cause, it certainly extends the intervals between necessary trips to the garage for maintenance or repairs.

Converting Your Diesel Engine to Run on Cooking Oil

As we've established, simply fuelling your car with unmodified cooking oil presents a multitude of mechanical problems. However, for those determined to pursue this alternative, it is possible to modify your vehicle to better accommodate cooking oil. This involves a more extensive and costly conversion process.

The first and perhaps most crucial modification is the installation of a second, entirely separate fuel tank specifically for the cooking oil. Having dual tanks provides the driver with the flexibility to choose between using regular diesel or cooking oil at any given moment. Crucially, the car will always start on diesel, as cooking oil is too viscous for cold starts. The cooking oil tank is typically heated, often by routing engine coolant through it. This heating process is vital as it significantly reduces the oil's viscosity, ensuring it flows more freely through the fuel lines and atomises more efficiently when injected into the engine's cylinders, leading to better combustion.

Beyond the dual tank system, the engine itself requires several other specialised upgrades. This includes fitting new fuel injector nozzles that are designed to handle thicker fuels and incorporate better filtration. Specially designed glow plugs, which are essential for igniting the fuel in diesel engines, are also often required. Furthermore, new or modified coolant lines may be needed to facilitate the heating of the oil tank. When you factor in all these components and the labour involved, the estimated conversion cost for a full system can be around £2,000 in the UK.

It's worth noting that a number of conversion kits for diesel cars are available on the market for those wishing to undertake this modification. While some brand-new vehicles are sold with HVO compatibility, such as certain Mercedes Unimog off-road trucks, these are highly specialised vehicles and certainly not practical family transport for the average consumer.

Do You Need Clean Cooking Oil to Fuel Your Car?

Under no circumstances should you ever contemplate pouring used cooking oil directly from your frying pan into your car's fuel tank. Such oil is laden with food particles, fats, and other impurities that will rapidly and irreparably clog your engine's intricate fuel system. While it's theoretically possible to filter domestic WVO by straining it through fine fabric, this is an incredibly fiddly, messy, and time-consuming process. Moreover, a single domestic kitchen is highly unlikely to generate anything near the volume of WVO required to fill a typical car's fuel tank.

However, WVO filtration is a substantial commercial enterprise, estimated to be worth almost £6 billion globally in 2019. Large-scale oil suppliers, such as Oileco and Cator Oils in the UK, primarily source WVO from commercial kitchens, restaurants, and other industrial sources. The UK alone generates over 100,000 tonnes of this material annually. This commercially collected WVO undergoes rigorous, multi-stage filtration processes to ensure it is clean and pure enough to be used as a viable fuel. A famous example of this practice is McDonald's, which notably runs its fleet of commercial delivery vehicles on WVO collected directly from its restaurants' fryers.

Filtered WVO is generally more accessible to commercial vehicle fleets due to the large volumes they require. For individual drivers, finding a supplier willing to sell smaller quantities can be challenging, and you might have to commit to buying in bulk. That said, there might be an enterprising local chip shop that filters and sells its own WVO, offering a potential, albeit rare, source for the individual motorist.

What's the Difference Between Vegetable Oil and Biodiesel?

It's important to distinguish between raw vegetable oil and biodiesel. Essentially, biodiesel is vegetable oil that has undergone a chemical process to remove its glycerine content – the substance responsible for oil's thick, gloopy consistency. However, simply removing glycerine isn't enough to qualify a fuel as biodiesel. True biodiesel must adhere to a stringent set of standards and specifications before it can be legally sold and marketed as such, standards which raw cooking oil does not meet.

According to Oileco, one of the UK's largest WVO refiners, biodiesel boasts significantly cleaner combustion, burning approximately 88% cleaner than standard regular diesel. This makes biodiesel an attractive option for those looking to reduce their carbon footprint. However, it's not entirely without its own set of environmental considerations. The extensive cultivation of crops specifically for biofuel production can sometimes lead to reduced biodiversity and the diversion of valuable agricultural capacity away from food production, raising ethical concerns about land use.

Is Using Cooking Oil in My Car Cheaper? The Financial Reality

For many, the primary motivation for considering cooking oil as a fuel alternative is cost. Until early 2022, a significant portion – 80% – of the sunflower oil sold in the UK was sourced from Ukraine. Following the invasion of Ukraine by Russia, the price of all cooking oils spiked to an unprecedented all-time high, significantly impacting its viability as a cheap fuel source.

At the time of writing, a litre of supermarket own-brand vegetable oil typically retails for around £1.99. In stark contrast, the average cost of a litre of regular diesel is approximately £1.53. From a purely price-per-litre perspective, the maths clearly do not favour cooking oil.

While it might be possible to source cooking oil more cheaply by buying in bulk from a cash-and-carry or online retailers like Amazon, or even from WVO sellers on platforms like Facebook Marketplace and eBay, these options come with their own caveats. Bulk purchases can be substantial upfront investments, and WVO sourced this way will almost certainly require extensive filtering, which significantly reduces the final usable volume of oil you started with.

Once you factor in the considerable conversion cost of modifying your car's engine to run on vegetable oil (estimated at around £2,000) and any necessary filtration equipment for WVO, the supposed cost savings quickly evaporate. Unless you are exceptionally fortunate enough to find a friendly local chip shop willing to sell you cheap, pre-filtered WVO on a consistent basis, it is generally far more economical and mechanically sound to stick with the black pump and regular diesel fuel.

Cooking Oil as Fuel: A Comparative Overview

Frequently Asked Questions (FAQs)

Can I put cooking oil in my petrol car?

Absolutely not. Cooking oil is far too thick and has different combustion properties that will severely damage a petrol engine, leading to blockages and ignition failures.

Will cooking oil damage my diesel engine?

Yes, if used directly or without proper modification. Its high viscosity can clog fuel injectors, filters, and lines, and it can confuse sensors, leading to costly repairs. Even in older diesels, problems are likely.

How much does it cost to convert a car to run on cooking oil?

A full, professional conversion of a diesel engine to run on cooking oil, including a second heated tank and modified components, can cost around £2,000 in the UK.

Does using cooking oil as fuel make my car smell?

Yes, it often results in a distinct, lingering smell of cooking chips from your exhaust, which can be quite noticeable.

Is using cooking oil environmentally friendly?

While biodiesel (a refined form of vegetable oil) burns significantly cleaner than regular diesel, the process of growing crops specifically for biofuel can raise environmental concerns regarding biodiversity and the diversion of agricultural land from food production.

Is it legal to run my car on cooking oil in the UK?

The legality often hinges on whether appropriate fuel duty has been paid. Unlicensed use of cooking oil as fuel to avoid duty can lead to fines and seizure of the vehicle by HMRC. Always ensure compliance with fuel regulations if considering alternative fuels.

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