How to Tell If a Vehicle Is Using Red Diesel

Written by Danny Collins
Last updated: June 1, 2023

Red diesel is a popular off-road fuel that finds its application in various industries such as agriculture, construction, heating, mining, and powering diesel generators, among others. It is essentially the same as regular diesel but with a red dye added to differentiate it and prevent its illegal use on road-using vehicles.

Red diesel is subject to different taxation regulations, and tax is not paid on this particular fuel. This article aims to provide insights into how one can identify if a vehicle is using red diesel, focusing on the UK context.

What is Red Diesel?

Plastic jerry can with red diesel inside

Red diesel, also known as gas oil or agricultural diesel, is a specialised fuel used predominantly in off-road vehicles and machinery. It shares many similarities with regular diesel in terms of chemical composition and performance. However, the distinctive feature of red diesel is the addition of a red dye, which acts as a marker to indicate its intended use and differentiate it from the diesel used in road vehicles.

Why is Red Diesel Illegal?

Red diesel itself is not inherently illegal; rather, its usage on certain types of vehicles is strictly prohibited. The legality of red diesel usage revolves around the payment of appropriate taxes.

In the UK, red diesel is subject to a lower level of taxation compared to regular diesel, making it more affordable for industries operating off-road vehicles. However, using red diesel on road-using vehicles, such as cars, vans, and trucks, can be considered as tax evasion, which is illegal.

If a vehicle is found to be using red diesel on public roads, the consequences can be significant. While there is no immediate fine for using red diesel in a road vehicle, the owner may face charges from Her Majesty’s Revenue and Customs (HMRC) for the restoration of the vehicle’s system. This includes expenses associated with cleaning the fuel tank and filters to ensure compliance with legal requirements.

3 Signs a Vehicle Is Using Red Diesel

Red Dye Marker

Red dye

One of the most apparent signs that a vehicle is using red diesel is the presence of a red dye marker. Red diesel is dyed with a distinctive red colour to distinguish it from regular diesel. If you come across a vehicle emitting red-coloured exhaust fumes or notice red staining around the fuel cap or on the hands while refuelling, it is a strong indication that red diesel is being used.

Vehicle is Untaxed

Untaxed car

Another sign to look out for is the absence of valid taxation. Vehicles running on regular diesel or other fuels must be taxed appropriately. However, vehicles using red diesel are not subject to road tax, as this type of fuel is intended solely for off-road use. If a vehicle does not display a valid tax disc or digital tax status, it may suggest the usage of red diesel.

Higher Sulphur Content

Sulphur gas cylinders

Red diesel generally contains a higher level of sulphur compared to standard diesel fuel. This is because the fuel is not subject to the same stringent environmental regulations as regular diesel used in road vehicles. While it may not be feasible to test the sulphur content directly, a distinct and pungent smell from the vehicle’s exhaust could indicate the use of red diesel.

Frequently Asked Questions

Is Kerosene the Same as Red Diesel?

No, kerosene and red diesel are not the same. Kerosene, also known as heating oil, is a different fuel primarily used for heating purposes in domestic and commercial settings. While both fuels share similarities, red diesel has a lower tax rate and is specifically formulated for off-road use.


Is Red Diesel Toxic?

Red diesel, like regular diesel, contains various hydrocarbon compounds and combustion byproducts that can be harmful if not handled properly. It is important to follow safety precautions while handling and storing red diesel, such as using appropriate containers and ensuring proper ventilation. It is essential to adhere to safety guidelines and regulations to minimise any potential risks associated with fuel handling.


Why is Red Diesel Cheaper?

Red diesel is subject to a lower level of taxation compared to regular diesel. The reduced tax rate is designed to support industries that rely on off-road vehicles and machinery, such as agriculture and construction. By offering a more affordable fuel option, it aims to facilitate the growth and productivity of these sectors.


What Happens if I am Caught with Red Diesel?

If you are caught using red diesel in a road vehicle, the consequences can be severe. While there is no immediate fine, you may face charges from HMRC for tax evasion. The charges can include the cost of restoring the vehicle’s system to comply with legal requirements, such as cleaning the fuel tank and filters. It is important to note that the responsibility lies with the vehicle owner to ensure that the correct fuel is used.


Can I Check if My Car’s Previous Owner Used Red Diesel?

Identifying whether the previous owner of a vehicle used red diesel can be a difficult task. However, there are several indicators that can offer some clues or insights. Firstly, you can inspect the fuel system for any signs of red dye residue, such as around the fuel cap or on fuel filters. Additionally, you can check the vehicle’s service history or contact previous owners to inquire about the fuel used. However, it is important to note that these methods may not provide conclusive evidence, and it is advisable to rely on the current fuel status and proper fuel documentation.


Identifying if a vehicle is using red diesel requires attention to specific signs and factors. The red dye marker, untaxed status, and potentially higher sulphur content are indicative of the usage of red diesel. However, it is crucial to note that red diesel itself is not illegal but rather the use of it on road-using vehicles. Compliance with taxation regulations and using the appropriate fuel for specific vehicles are essential to avoid legal repercussions. If there are any doubts about the fuel type used, it is advisable to consult local authorities or experts for guidance.