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What’s in your fuel? Common Contaminants and the Damage they do

What’s in your fuel? Common Contaminants and the Damage they do

What’s in your fuel? Common Contaminants and the Damage they do

What’s in your fuel? Common Contaminants and the Damage they do

Having clean fuel is essential if your engines are going to run as they should.

Contaminated fuel has a big impact across your engine – reducing efficiency and performance, impacting on lifespan and reliability and increasing emissions. It’s why fuel filtration is so important, and why it’s vital that you specify the right, high quality fuel filters, filter assemblies and accessories for your machinery.

In this guide, we take a quick look at a list of the most common contaminants. We examine how they get into the fuel, and the damage they can do to your vehicles and machinery.

Dirt, debris and particulate

Diesel might look clean, but storage tanks are rarely 100% airtight. Over time, tiny dirt particles get into fuel, and additional particulates get into the diesel whenever it’s transferred between storage tanks.

These particulates can cause friction damage to the engine and wearing on the injectors, which will reduce their lifespan. They can also disrupt engine combustion – reducing efficiency and performance, whilst increasing the engine emissions.


Water in your fuel is bad news. Like dirt and debris particles, water gets into fuel whilst it is in storage. It reduces the lubricity of fuel, and can cause corrosion throughout the fuelling system – reducing the efficiency and lifespan of the engine, whilst creating further corrosive contamination within the engine itself.

In addition, water negatively impacts on the combustion process. It can damage system components and significantly reduce performance.


All diesel fuel contains paraffin. In the cold winter months, this can freeze, forming crystals of wax in fuel storage tanks and vehicle tanks. These don’t unfreeze – once waxing has occurred, the wax crystals don’t melt. Instead, wax builds up, blocking the fuel line and choking the engine, starving the engine of fuel and causing damage.

Bacteria and fungus

Bacterial microbes and fungal spores can thrive in fuel tanks if the conditions are right (especially if there is some water contamination) and over time, they build up. It doesn’t matter whether you’re using diesel, red diesel, jet fuel or biodiesel - if they are not filtered out properly, these microbes begin to ‘eat’ the fuel, degrading its quality and causing widespread fuel system corrosion.

If not managed properly, using the right fuel filters, fuel will eventually degrade into a slimy sludge. This can render the whole tank of fuel unusable.

Fuel Degradation Products

Fuel has a shelf life, and over time, it starts to degrade – thanks to its oxidative instability.

Gums, sediments, acids and thickeners begin to form in the fuel, which then start to hamper engine performance. Filters get clogged, and the particles cause abrasive damage to key parts within the fuel system. The fuel can also become more viscous, reducing fuel economy and engine performance. Acids start to corrode the tanks and fuel systems, reducing the lifespan of components.


Asphaltenes are compounds naturally found in crude oil – but more recently, they are becoming more prevalent in refined fuels as well, especially with the introduction of ULSD (Ultra Low Sulphur Diesel).

Asphaltenes form over time (especially when water is present), and manifest themselves as a black, tar like sludge. This can quickly clog up fuel system components, like the fuel injectors and fuel filters.

How Alexis Filters can help

Whilst proper storage, regular maintenance and the right additives are all part of the solution, keeping fuel clean starts with choosing the right fuel filters and filtration systems.

Alexis Filters are fuel filtration specialists – providing a comprehensive range of high performance fuel filtration products and replacements for all kinds of vehicles and machinery, across a full range of industries.

Choose Alexis, and you’ll benefit from the best prices on quality components from leading brands like Donaldson and HiFi, responsive, personal service and expert advice on all your filtration needs.

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“I moved over to ALEXIS FILTERS some 4 years ago when our previous supplier changed brands. Since then the staff have helped with the transition to DONALDSON which is a quality product. They have been very helpful and the service has been very good especially on short notice requirements usually having whatever we need on stock!”

Chris Adaptable