Diesel Bug

Diesel Bug: What is it?

26/2/2024

Diesel bug

Diesel bug describes the fungi, bacteria and other microbes which grow on fuel tank walls, and at the point where stored diesel fuel meets water. Its sediments and slimy strands can clog and contaminate stored diesel and fuel lines. This can even lead to engine failure in vehicles and machinery.

If you’ve ever seen a pond clogged with algae, similar things can happen to standing diesel stored in fuel tanks when diesel bug gets out of control. The bug also excretes an acidic substance for good measure, risking corrosive damage to fuel tanks over time.

How to get rid of diesel bug

Ask anyone who knows about diesel bug and you’ll hear the words “prevention is better than cure”. This is really about depriving diesel bug microbes of the water they need to survive and breed.

Diesel bug test kits are widely available to identify fuel tank infestations.
Biocide treatments in high doses kill off microbes within the fuel tank, either by starving or dehydrating them.
Dispersant treatments use detergents to suspend water molecules within the diesel fuel, so that any unwanted water leaves the tank with the fuel and is burned up by the engines as it enters.

Smaller maintenance doses of biocide and dispersant additives are actually best used from the very first time you fill a fuel tank, to keep the risk of diesel bug constantly in check.

Regular use of an additive will help ensure that your fuel tank’s environment stays hostile to fuel bug microbes, which should prevent breakouts of the bug over the long-term.

But in the case of full diesel bug contamination, you can’t just use these treatments alone.

Where diesel bug has run rampant, a contaminated diesel storage tank and its fuel lines will still need to be cleaned of the dead microbial matter that a biocide leaves behind. Otherwise, fuel lines, fuel filters and engines will still suffer from a dark, grainy debris that continues to enter hoses and machinery, clogging up components and burning pretty unpleasantly during an engine’s combustion.

Diesel bug contamination can also damage tanks, pipes and components – so it’s well worth checking for any leaks or deterioration in your fuelling hardware after the bug is gone, or better still arranging for a professional fuel tank service to make sure.

Reduce the risk of diesel bug with regular maintenance.

A proactive schedule of fuel testing and maintenance is always the best way to keep on top of any potential diesel bug present in your fuel. But the best strategy of all is to make your fuel tank a hostile place for the fuel bug to live.

Diesel bug hates dry and well-bunded fuel tanks that are used, emptied and refilled regularly. It struggles to grow in fresher fuel which is churned and circulated frequently, especially if that fuel is free of any water, and fortified with additives which kill off those microbes from the start.

There are actually many ways to avoid a diesel bug infestation:

Buy a good-quality diesel fuel and maintain it regularly
Apply an effective preventive treatment frequently, from your tank’s first use
Regularly check your fuel’s appearance for clouding or slime
Test for water and diesel bug mainly at the bottom of your tank
Perform regular tank maintenance and inspections
Schedule regular use of diesel bug testing kits
Have your fuel expertly tested every six months; ideally mid-summer and mid-winter
Use up and refill your stored diesel regularly
Use a fuel recirculation system to avoid the still, standing fuel that diesel bug grows in
Choose a fuel tank designed to radically minimise moisture
The more fuel in the tank, the less space for moisture formation (and diesel bug)
Better to fill and empty a smaller tank regularly, than leave a big tank constantly half-full.

How does diesel bug infestation happen?

Diesel bug relies on the presence of water within a fuel tank, making moisture the number one enemy of anyone storing diesel fuel.

Diesel bug microbes can even sit dry and dormant, just waiting for water to come along.

Rust, cracks, condensation, ground moisture, puddled rainwater and poorly welded tank seams can all give diesel bug the water it needs to spread, and to contaminate a fuel tank and its contents.

Since water is denser than diesel, any water present in a diesel tank will sit beneath the stored fuel in its own separated layer. It’s at the midpoint between these layers of diesel and water that diesel bug survives and spreads exponentially, forming a dark gelatinous mass called biofilm – and causing a whole host of problems too.

What does diesel bug do?

Growing in standing water, diesel bug feeds on stagnant diesel and breeds rapidly, contaminating whole fuel tanks with engine-clogging sediments and eggy-smelling slime. This charming sludge can clog fuel filters, block diesel fuel injectors, and even lead to the costly breakdown of engines and machinery. All of which can cause expensive delays, often when tight deadlines need to be met.

Better yet, diesel bug also excretes acidic waste. This waste is capable of corroding steel fuel tanks over time, which can even lead to leaks and oil spills in extreme cases, when these microbes are allowed to grow and spread unchecked.

Diesel bug symptoms

A diesel bug infestation comes with warning signs:

Your vehicle’s engine doesn’t start up as strongly.
Thick, black, sooty smoke from the exhaust, with a sulphur-like odour.
Your vehicle consumes more fuel than usual.
Engine failure or a noticeable loss of power.
Your diesel fuel looks clouded and murky.
Fuel pumps, lines or injectors are clogged with dark sludge.
You find yourself cleaning or replacing fuel injectors more often.
Engine components wear down faster and need to be replaced.
You find yourself changing blocked filters more regularly.
Fuel filters are mudded up with a dark, grainy sediment.

Clogged engines

A temperamental diesel engine could secretly be choking on diesel bug biomass. If your vehicle or machinery is starting to cough and sputter, or if it just isn’t giving you as many horses as it should, then this could be down to clogged lines and fuel injectors – or even internal combustions that aren’t firing correctly. Less power, less efficiency, poor performance… it could be the bug.

Blocked fuel filters

Shorter lifespans for your fuel filters can be a sure sign of diesel bug blockage. Check your filter for any hint of slime or dark debris, and you can be pretty confident in that case that there’s a diesel bug problem to take care of. This issue really just gets worse for contaminated fuel, so the faster you act, the more work (and money) you’ll save later in clearing and cleaning your fuel tank, and fuel lines.

Clouded fuel

Both white and red diesel are crystal clear, so any clouding is a dead giveaway for the presence of water molecules in your fuel. This is the same water content which, if allowed to stand and separate, gives diesel bug microbes the perfect environment to replicate and spread. (Which they can do in a matter of minutes, and many many times over.) Schedule regular visual fuel tests, and check your fuel tank for any signs of rust or leakage – especially underneath, where rust often spreads unseen.

What causes diesel bug to grow?

Microbes need a food source, which they’ll even find inside a sealed diesel tank. In the words of Jeff Goldblum, “Life, uh, finds a way.”

Diesel bug feeds on the hydrocarbons that make up diesel fuel. It thrives on standing diesel fuel which hasn’t been used for a while – and especially with modern mixes, which contain biodiesel.

FAME biodiesel (Fatty Acid Methyl Ester) is made from vegetable oils, making it better for the environment – but it’s also a better food source than mineral diesel for microbes to grow and multiply.

As for water, diesel bug will exploit any rusty leak or condensation which makes contact with fuel inside the tank. Even as a diesel tank warms and cools through the day and night, the condensation that forms can allow diesel bug to grow.

But diesel itself is also highly hygroscopic, meaning it absorbs moisture from the air around it. This effect is even more pronounced in FAME (vegetable oil) biodiesel, which is now added to mineral diesel in increasing amounts.

Better for the environment is brilliant, and that means better for living things – but that also includes diesel bug!

Minimise diesel bug with the right fuel tank design

Diesel bug microbes are a fact of life, especially with the increasing use of FAME biodiesel added into the mix. While processes like fuel polishing can clean and decontaminate fuel tanks affected by diesel bug, really the best approach is to prevent fuel bug proactively, right from the start.

The risk of diesel bug can be drastically minimised with the right maintenance and additive schedule, and especially with the right fuel tank design.

We specialise in building cylindrical fuel tanks because they’re structurally the strongest, and need fewer welded seams, but also because they’re far more water-resistant. A cylinder on its side lets rain and condensation roll right off, so there’s nowhere for the water to pool on the tank’s surface and potentially turn to rust and leaks. Likewise, our tanks are suspended above the ground (and ground moisture), and every square inch is painted in two coats of extremely tough polyurethane paint. All of which minimises the risk of rust.

Minimise rust, and you minimise corrosion. Minimise corrosion, and you minimise the risk of leaks where water can enter the tank, contaminate your fuel, and create the perfect conditions for diesel bug to grow.

But even in the unlikely event that water enters a cylindrical fuel tank, (and given the fact that some condensation will be present in any fuel tank, regardless of its design), a cylinder’s basic cornerless shape will still keep any standing water to the smallest possible surface area, at the bottom of the tank. Combined with our tanks’ angled positioning, simple gravity reduces the surface area for water even further – and so radically minimises the potential for diesel bug to spread.

Since our tanks’ sloping-cylinder design causes any water to collect at the lowest point inside, we can then use a sump pump at this point to drain it out quickly and easily. This just isn’t possible with a flat-bottomed tank.

You’re welcome to read more about our industry-leading bulk fuel tanks right here – or you can head to our Downloads page, where you’ll find detailed specifications on our full fuel tank range.

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