Microbial fuel contamination is unfortunately common when storing red diesel (gas oil), white diesel (DERV), biodiesel and heating oil (kerosene).

More often than not, when our customers purchase fuel, they keep it in storage and then forget about it until they need to use it – out of sight out of mind one might say. So it can be a huge surprise when it fails to do its job when it's needed the most.

Even the best quality fuels will degrade over time when stored, and it's important to be able to spot the warning signs and take action as soon as possible. One of the most common problems with diesel engines is microbial fuel contamination. Fuel owners and users must regularly be on the lookout for signs of contamination or degradation – both which can cause significant problems.

Contamination spreads quickly in industrial machinery, grain dryers, generators, milk bottling machines or anywhere else where diesel is used and can render your fuel useless if you don’t take steps to prevent it. Fortunately, these problems can be avoided through the implementation of planned preventative maintenance solutions and regular fuel testing.

The cause of microbial fuel contamination

Changes to fuel specifications brought about by rigorous emission regulations for engine designs to meet a higher level of fuel cleanliness have led to a greater need for regular fuel testing to prevent and manage fuel contamination.

In 2004, the British Standard for off-road diesel (BS2869) was amended to mandate up to 7% fatty acid methyl ester (FAME) to be included in white diesel (DERV) to allow renewable fuels to be introduced under the Renewable Fuel Transport Obligation (RFTO).

Biodiesel is a diesel replacement manufactured from renewable materials such as animal fats and plant oils. The production process converts the oils and fats into long-chain molecules called fatty acid methyl esters (FAME).

FAME offers several benefits over traditional fuels such as reduced emissions, low toxicity, low sulphur and biodegradability. However; unlike diesel, FAME is hygroscopic and the methyl esters absorb significantly more water than petroleum-derived diesel and hold it in suspension in the fuel.


FAME is very different from diesel chemically and can cause problems with engine and fuel systems if used in high concentrations. It's the perfect source of nutrients for microbes to grow, leading to foaming, reduced stability and gelling at lower temperatures.

Tips on how to avoid diesel fuel contamination

It's now more important than ever for businesses to have emergency backup and fuel storage facilities to implement planned preventative maintenance strategies into their operations. To avoid the huge costs and inconvenience associated with fuel contamination it's important to follow these steps:

• Have professional inspections annually (at least) – investing in regular fuel tests by a professional company will keep your fuels and oils in good condition and help tackle the problems of microbial fuel contamination. We actually suggest a fuel test twice a year; once before the winter months and again before the spring, as these seasons are the most problematic for your fuel system.

• Buy from a reputable supplier – while oil is a commodity, it's important to shop around and make sure that you're purchasing from a trusted company. If you see unusually low prices, it's likely because it's poor quality and will do more damage to your fuel system than good.

• Maintain your fuel tanks – while regular fuel tests are crucial, it’s also important to invest in tank cleans at the same time. If you put clean fuel into a corroded or damaged tank, it will simply contaminate the fuel again straight away – a waste of time and money!

• Rotate your fuel usage – if you have several bowsers or tanks that you use to store fuel, ensure that you rotate their use regularly so you're using the oldest fuel first.

• Keep your tanks topped up – by minimising the amount of empty space within your tank, you're also reducing the chances of water condensation forming. This, in turn, reduces your risk of microbial contamination.

What to do if your fuel is contaminated

If you suspect that your fuel is contaminated, get in touch with Beesley Fuels today on 0330 158 8225. The longer you ignore contaminated fuel, the worse the problem will get.

We'll collect a fuel sample

Our engineers will come to your site and take samples from the top, middle and bottom of your tank so we can get a full picture of the condition of your fuel. They'll also perform a visual inspection of your tank, checking for the tell-tale signs of corrosion or damage.

We'll test it

Our industry-leading onsite technicians can test for fuel contamination in a large diesel fuel tank, bowser, generator, boiler or any other storage facility you have. They will analyse and test it in our state of the art onsite laboratory to look for signs of water, bacteria, bugs, particulates and provide you with an easy-to-interpret analysis in a detailed report.

If possible, we'll polish it

If possible, we can then come back to your site with a fuel polishing unit and clean it and return it to its former quality, so it's as good as new. This is a more cost-effective option than replacing your entire fuel stock. Learn more about our fuel polishing service here.

If not, we'll uplift and replace it

If your fuel is severely contaminated, it may be that it cannot be polished and instead needs replacing. We can uplift the dirty fuel and take it away and supply you with a fresh, clean fuel delivery. It's that simple!

We'll clean your tank no matter what

Whether you need your fuel polishing or replacing, we will always carry out an industrial tank clean to avoid the fuel becoming re-contaminated.

To avoid the troublesome consequences of fuel contamination, get in touch with the fuel experts on 0330 158 8225 today.