DIESEL BUG – THE BLACK DEATH!! (Part 1)
Sludge, the Black Death, Microbiological Growth or DIESEL BUG!!! Whatever you call it it's basically just a combination of Bacteria, Yeast and various Fungal infections in your vessel's fuel tank/s. A serious problem if you are unfortunate enough to get a bad dose of it.
Diesel Bug blocks filters, causes loss of power, poor fuel economy, excessive wear to your fuel pump and injectors and can result in your engine/s shutting down at the most inopportune time.
Some will say they've never had it while others have had a nightmare dealing with it. What is not commonly known though is that all diesel fuel carries the bug, it's just that in most cases the levels of microbial contamination are low and normally well within acceptable limits. The problem arises when the environmental conditions in fuel storage systems change. And yes your vessel's tanks are fuel storage systems!
When water is allowed to ingress or become present in your fuel tanks and the temperature is right it provides an ideal environment for microbial growth to occur (Diesel Bug to grow). This can result in loss of fuel quality and problems with blocked filters and in severe cases blocked fuel lines as well. However, while heavy infections are not uncommon they only usually occur as a result of inaction, either because the vessel has remained out of action for quite sometime or because no action was undertaken when signs of the bug were first noticed. Usually contamination can clearly be seen in your primary filter sight glasses or water collection bowls.
Water that enters the fuel tends to drop out and result in what is known as Free Water. This water can sit in the bottom of your tank under the fuel and may at some stage get picked up and deposited along with the bug in your fuel water separators. In addition very small amounts of water can become emulsified in the fuel (normally the result of a Yeast infection). Water, in particular saltwater can result in corrosion of fuel tank linings, pipework and metals including aluminium and even stainless steel in severe cases.
Micro-organisms can selectively degrade various hydrocarbon components of the fuel and fuel additives (supplier blended not the after-market types). Dozens of different micro-organisms (bacteria, yeast or fungi) can grow in fuels depending on the conditions present. This makes the fuel particularly vulnerable to contamination during transportation and prolonged storage, which is why the marine industry is hit so hard with the problem. Many of the additives in fuel act as nutrients for the growth of these various organisms with most of the visible contamination occurring at the fuel-water interface. This is something that can clearly be seen when visible free water is present in the fuel.
A couple of points worth noting here is that as the Government and fuel companies introduce lower sulphur levels into our fuel stocks one of the draw backs I understand from experts in the industry is that it will allow microbial growth to prosper. High sulphur levels in the past have assisted in suppressing the bug unless water ingress became a problem and resulted in the perfect environment for the bug to grow. With sulphur levels in our fuel dropping those with fuel storage systems that store fuel for long periods of time may feel the effect. Another issue that has come to light lately is the introduction of Biofuels. With the added nutrients available the bugs will have a field day so good housekeeping in conjunction with a suitable on-going treatment process will be an absolute must.
As it only takes very small amounts of water to kick start the microbial growth into life it is imperative that any water is kept at bay. In the marine environment water can ingress a number of ways. Aboard vessels we generally see three types of water – them being saltwater, fresh water and condensation or in some cases a combination.
Seawater can enter via incorrectly placed breathers and deck filler points (replace your o-ring seals in these fittings yearly) while fresh
water can enter similar ways particularly after a trip when you are washing the vessel down with hose tap water. Condensation on the other hand is caused by the tanks breathing in moist air and allowing it to build up on the walls. This can occur when wall space is available i.e. when the fuel tanks are half full or less. Therefore the simple answer is to keep your tanks above 80% full most of the time and to use the top third of the fuel in your tanks not the bottom third. Understandingly for various reasons this may not always be possible, however, at least try to full them up just before the onset of winter as months of inaction can start the problem off and leave you with a headache just in time for the up and coming season.
Another good way of keeping water at bay is to drain off a small amount of fuel from a low point in the tank. That's of course if you have a drain valve. Hopefully any water will have settle to the bottom close to the valve and will drain out before or with the fuel. A clean white container comes in handy here so as to observe the quality of the fuel.
Well that's all for this month. Next time we continue this subject and look at the different types of microbial contamination and some useful ways of dealing with it.
Written for Professional Skipper Magazine, Issue 67
Written By Kelvin Hieatt
Marine Diagnostics Ltd
Specialists in Used Oil and Petroleum Analysis
