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Diesel Bug Contamination Guide

Diesel bug is an increasing problem as FAME content increases in UK fuels. But luckily, it can be avoided with some simple steps. Our guide explains everything there is to know about diesel bug

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Your Guide to Beating Diesel Bug Contamination

Diesel bug is responsible for 8 out of 10 diesel engine failures. At Crown Oil, many of our customers come to us as they are struggling to cover the rising costs and damage from using diesel bug-contaminated fuel. Therefore, knowing what causes it and how it can be avoided is key in helping keep your business running smoothly.

Diesel bug poses an increasing problem as FAME content increases in UK fuels, but luckily, following some simple steps can help save your stored fuel from causing damage to your equipment.

diesel bug contamination

What is diesel bug?

Diesel bug, also known as fuel bug, diesel virus or diesel fungus, is a term used for microbial and bacterial organisms and their subsequent reaction product. It’s not just one single type of organism; there are many variations found living in fuel systems, which largely fall into four categories:

  • Degrade the quality fuel over time
  • Single-cell organisms, generally from 0.3 to 60 micrometres in size
  • A group can double its numbers in 20-30 minutes
  • One cell can multiply into 2 million in 7 hours
  • A form of fungi with long multi-cellular filaments
  • Due to its long strands, it blocks filters
  • Relatively slow-growing fungi
  • Typically, 3-4 micrometres
  • Complex structure of microbes which stick together and to tank walls
  • Begins to form when free-floating microbes fall on tank walls and attach to it
  • Grow drastically over time and produce a protective slime
  • Excrete acid which can corrode metal fuel tanks
  • Slough off periodically, providing microbes with the opportunity to infect other areas of the fuel system and block filters

What causes diesel bug?

Diesel bug is caused by the presence of water in the fuel combined with FAME biodiesel that is blended with all mineral diesel. The FAME content in the diesel allows water to mix in the diesel and the bio content of the biodiesel acts as a food source for microbial growth.

More technically, diesel fuel contains up to 7% biodiesel by volume which is great for the environment and improving air quality but not so great for your engines or machinery. Biodiesel and diesel producers are consequently sometimes facing stability issues due to legislative increases in FAME content.

Regular biodiesel (FAME) consists of fatty acid methyl esters with differing degrees of saturation which are at risk from oxidation. FAME is hydroscopic which means it attracts water and increases diesel bug attack over time, meaning these fuels must be closely monitored to avoid equipment and machinery failure.

Diesel remains stable in normal storage conditions for up to 12 months. After that, it begins to deteriorate in quality as it reacts with oxygen from the air. At this point, sediments build up which can be pulled through the fuel lines and clog filters.

Water in the fuel is the biggest contaminant for diesel fuel. This combined with fuel (hydrocarbons) and typical UK mild temperatures create the perfect breeding ground for contamination.

Oil storage tanks heat up during the day and cool at night, which can cause condensation to form on tank walls, as well as rainwater ingress and absorption from the air. This creates the perfect conditions for bacteria to flourish in stored fuel.

Diesel bug lives at the point of blend between water and diesel or on the tank walls, creating a sludge which will damage your tank and engine. It multiplies rapidly and doubles in size every 20 minutes. This means that it doesn’t take long for diesel bug to amalgamate and cause mayhem within the tank and engine.

What does diesel bug look like?

Once built up, diesel bug often has the appearance of slime. Its colour depends on the type of bug, varying from a dark brown to a blackish shade. It often smells like rotten eggs.

Signs of diesel bug

  • Blocked filters and injectors that regularly need changing
  • Sediments in filters that have a coffee-like appearance
  • Engines suddenly lose power
  • Egg-like smell
  • Fuel discolouration
  • Black smoke from the exhaust
  • Corroded fuel tank
  • Increase in fuel consumption
  • Problems starting engines

How to avoid diesel bug

As the old idiom says, prevention is always better than a cure. The key to good fuel quality is good maintenance.

  • Get your fuel regularly tested by a professional company at least twice a year, ideally once before summer and again before winter
  • Ensure your fuel tank is sealed as airtight as possible
  • Ensure a regular fuel maintenance programme
  • Full tanks have less room for moisture accumulation – keep your fuel tank topped-up.
  • Inspect tanks for damage and leaks
  • Ensure a regular turnover of fuel – diesel bug grows more easily if fuel is left dormant
  • Buy fuel from a reputable supplier

Are FAME-free fuels like HVO fuel affected by diesel bug?

Unlike fossil diesel, HVO fuel contains no FAME, bio and sulphur, allowing it to be a stable product that doesn’t react with water. This makes it far less susceptible to diesel bug attack and ensures its performance isn’t affected at both the point of use and after prolonged storage.

These properties allow HVO to be stored for up to 10 years, compared to up to 1 year for mineral diesel. It has a high purity and flashpoint which provides improved safety, storage and handling, reducing the need for regular testing and expensive fuel replacements.

How is diesel bug treated?

The best form of diesel bug treatment that will kill fuel bug is to treat the fuel stored in the tank via fuel polishing to remove any contaminants. However, if it’s too badly degraded, you must also get your fuel storage tank professionally cleaned; there’s no point in cleaning or replacing your fuel and then keeping it in a dirty tank.

If you suspect diesel bug is attacking your fuel, it’s important to get in touch as soon as possible. Call us today on 0330 123 1444 to ensure your business is protected all year round.

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