Fuel services · Diesel bug
Diesel bug treatment & removal
Blocked filters, black sludge and slime in your diesel tank? That's diesel bug: microbial growth living at the water/fuel interface. We test, treat and polish the fuel on site so your generator, fleet or plant keeps running.
- On-site fuel sampling and contamination testing
- Fuel polishing, water removal and biocide dosing
- Tank cleaning where sludge has built up
- Nationwide engineers covering the UK & Ireland
Get diesel bug sorted
Tell us what's happening and our service team will call you back with next steps and a price.
Signs you've got diesel bug
If you're seeing two or more of these, the fuel needs testing before it takes a generator or vehicle out of action.
Filters blocking early
Fuel filters clogging well before their service interval, often with a dark, slimy coating.
Black or brown sludge
Sediment at the bottom of the tank or in drawn samples. That's the dead biomass left behind by microbial growth.
Cloudy or dark fuel
Diesel that should be clear and bright looks hazy, with visible water or stringy material in it.
Loss of power or stalling
Engines running rough, losing power under load or failing to start, especially standby generators on test.
Rotten-egg smell
A sulphur smell from the tank or filter housing is a classic sign of active microbial activity.
Corrosion and pitting
Acidic by-products attack steel tank floors, pipework and injectors. That's the expensive end of an untreated bug.
What is diesel bug?
"Diesel bug" is the trade name for bacteria, yeasts and moulds that grow in stored diesel. They live in the water that collects at the bottom of a tank and feed on the fuel above it, producing a slimy biomass and acidic waste.
Modern diesel is more prone to it than it used to be: low-sulphur fuel and the biodiesel (FAME) blended into road diesel both hold more water and give microbes more to feed on. Tanks that sit part-full for long periods, such as standby generators, seasonal plant and farm storage, are the most at risk because condensation keeps adding water.
Dosing a biocide on its own rarely fixes it. The dead biomass still has to come out, and the water that started it has to go, or the bug comes straight back.
Where it starts
- Condensation and rainwater ingress leave a layer of water under the fuel.
- Microbes colonise the water/fuel interface and multiply in warm weather.
- Biomass and sludge get drawn into filters and injectors when the engine runs.
- Acidic by-products corrode the tank floor and fuel system.
How we treat it
One visit, one engineer, fuel kept in service wherever possible.
Step 1
Sample & test
Bottom-of-tank sample, water check and a microbial test so we know how bad it is before touching anything.
Step 2
Remove the water
Free water and the worst of the sludge are drawn off from the tank bottom and disposed of correctly.
Step 3
Polish the fuel
Fuel is circulated through multi-stage filtration to strip out biomass, particulates and emulsified water.
Step 4
Treat & protect
Biocide dosed to kill what's left, tank cleaned if sludge is heavy, and a retest to confirm the fuel is clean.
Who we help
Standby generators & data centres
Fuel that sits for months is the highest-risk fuel there is. We test on a schedule so it starts when it has to.
Fleet & depot tanks
Bulk storage feeding vans, trucks and plant. One contaminated tank spreads to every vehicle on it.
Farms & construction sites
Outdoor tanks, seasonal use and water ingress make agricultural and site tanks a regular callout for us.
Common questions
Can I just add a diesel bug treatment myself?
Off-the-shelf biocides can help as a preventative in a clean tank. Once there's visible sludge or recurring filter problems, the dead biomass and water still need removing or the problem returns.
Do I have to throw the fuel away?
Usually not. Fuel polishing recovers the diesel in most cases, which is far cheaper than disposal and refilling. We'll tell you from the sample if it's beyond saving.
How long does a visit take?
It depends on tank size and how much sludge there is. Most tanks are tested and polished in a single day; a full clean is longer. We'll confirm when we quote.
How do I stop it coming back?
Keep water out (lids, vents, bund checks), keep tanks as full as practical to limit condensation, and put a sampling and polishing schedule in place. We can set that up for you.
Not sure if it's diesel bug?
Fill in the form above or call us. A quick sample will tell you for certain, and it's far cheaper than a failed generator start.
