Diesel Polishing

The vast majority of boats we see on the inland waterways rely on diesel for propulsion. Like the rest of your boat, it is important to look after your fuel and fuel system. Neglecting this will eventually lead to diesel bug developing. This article talks about preventing diesel bug, diesel polishing and chemical fuel treatments.

Call Floating Boatyard on 07886 388 689 or contact us here if you think you may need diesel polishing.

What is diesel bug?

Diesel bug is a colloquial name for a host of different microbes (mainly bacteria but also yeasts and moulds) which live inside diesel tanks. These microbes live in water and feed off the biological components of your diesel.

Modern diesel is a biofuel mix. While this is better for the planet it is more prone to bug.  These microbes are most commonly found at the interface between diesel and water in your fuel tank. As they grow, reproduce and die, they form polysaccharide polymers (long, gross, slimy strands to you and I) which clog up the fuel system and cannot be burned by the engine. These microbes often produce acidic by-products, this can cause pitting and corrosion in steel fuel tanks – similar to how bacterial plaque build up on your teeth causes cavities.

Diesel Bug - Tanks Needs Diesel Polishing

Diesel bug residue in the bottom of a canal boat tank.

Diesel Polishing – Preventative Maintenance

With care, you can probably avoid the need for diesel polishing for some time. As diesel bug forms in water, preventing water ingress into your tank is key. Make sure your filler cap fits tightly, as rainwater could run down the screw thread and into your tank. Keep your fuel tank as full as possible. This prevents condensation on the walls, which drips into the fuel. Diesel which is allowed to sit for a long period of time (such as over winter) without being disturbed by running the engine is more prone to diesel bug. We recommend that you use a diesel additive such as Marine 16 as per manufacturers instructions. Especially if you are not using your engine on regular basis.

Diesel fuel – especially fuel with a higher biodiesel content – does have limited shelf life. We recommend that you buy your fuel from suppliers with a good turnover of stock. Most marinas and coal boats on the London waterways are always busy, but if you are venturing to lower traffic waterways this is worth bearing in mind.

The microbes which cause diesel bug do not come from one particular source, they are airborne and live on almost every surface of this planet. Ultimately, while you will never be able to maintain a totally sterile fuel system these tips should give you some respite from diesel bug problems.

Diesel Polishing – How Do I Know I Need It?

Usually, the first symptom of diesel bug is an engine which starts but cuts out. This also suggests issues with the fuel supply system in general. When fault finding, our mechanics will remove and examine the fuel filter. If diesel bug is present, it will show up in the filter as clumps of black slime. By this stage, the diesel big problem is usually very bad. For prior warning, keep up to date with your engine service intervals and pay attention to how your engine sounds. You might hear it struggle and cut out when in higher revs if the fuel system is getting blocked up.

We recommend checking for diesel bug once a year. This can be done by us as part of your annual engine service. You can also test the fuel yourself with a fuel testing kit.  If you find that the bug is present, then we recommend you also check the inside of the tank for corrosion.

Diesel bug seems to get worse when the weather warms up after winter. During winter, water collects inside the diesel tank. Microbes love temperatures around 30°C. When the diesel tank gets to a higher temperature, the population of microbes explodes. We get many calls in early June for bug problems. That said, it can be a problem that strikes at any time of year.

Diesel Polishing – How It Works.

If you find you have a diesel bug problem, the first stage is to use some Marine 16 as per manufacturers instructions. In less serious cases this is usually enough to clear it. The product kills the bug and breaks it down into materials which can be burned by your engine. If once you have tried this, you are still having problems with diesel bug, you will need diesel polishing.

A Diesel Polishing Machine Cleaning Diesel Bug

Our diesel polishing machine in action, filtering diesel bug from the fuel.

Attacking nasty diesel bug infestations needs a multi-pronged approach. The first step is to remove the diesel from the tank and polish it as we go. We have specialist equipment for this. Basically, the diesel fuel is pushed through filters which are fine enough to remove microbes and water but not the fuel itself. At this stage, we also recommend inspecting and cleaning inside the tank.

If your diesel tank does not have an inspection hatch, one will need to be made by us. At this point, it is usually a good idea to visually check for any signs of corrosion of steel tanks. At Floating Boatyard, we are not surveyors so do not offer full thickness tests. We will inform you if we see any signs of pitting or corrosion which looks concerning. After this, we clean out the tanks, removing any residual biofilms or other matter.

Finally, we put the diesel back and seal up the fuel tank. We then bleed your engine and start it up with some diesel treatment in the fuel. This ensures that the system is cleared from the inside. Any contaminants which find their way back into the diesel tank at this point will be at such low concentrations as to have no effect on the system, and the diesel treatment will take care of microbes.

For free quotes and consultations ring 07886388689 or message our here.

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