The good oil on fuel

Making sure your engine has good, clean fuel is just one way you can stack the odds in your favour to make sure it works when you need it, writes John Tylor.

It has been a trying day. A confused sea and un-forecast wind against tide have dogged you for hours and you are tired. Then to cap it off, the engine dies just as you reach the sea wall. You let the anchor go and while you sit waiting for a tow you calculate how much you will get when you sell the boat — just as soon as you get home that is. Far fetched? Not at all — it happens far
too often.

The fuel filter you changed only yesterday has suddenly choked with sediment that was stirred up from the bottom of the tank by the pounding. When the filter (which just did an admirable job of protecting the engine) filled up, the fuel stopped flowing, starving the engine. While there are few things as annoying as having an engine that is hard to start, one that stops right at the wrong moment can
be fatal. Good fuel management is one way to minimise these problems.

The main fuel contaminants are sediment and water and while most of the fuel we buy is good, how we store it can have quite some bearing on its quality when we need it later. Engines need three things to run well: clean air, clean fuel and clean oil. A quality air filter, even in the relatively clean environment we operate in, will ensure only clean air reaches the cylinders. Clean oil requires regular oil changes, usually every 100 to 150 hours — see the maintenance manual. But clean fuel requires more effort than just changing the filters at the specified interval.

Diesel fuel

Diesel engines are built to finer tolerances than most other engines, and while they will run forever if looked after properly, they are particularly critical of fuel quality. Poor fuel will not only clog filters and starve the engine, but damage the expensive injector pump or other engine components. While every boat should have a series of filters to remove contaminants, it is always better and safer in the long run to prevent the junk getting there in the first place. On my Duncason 35, Ard Righ, we buy our fuel from the local truck stop which has a high turnover. This ensures the fuel is as fresh as possible, then we syphon it from the jerry can into the boat’s tank via an inline filter.

Good fuel tank design can reduce many problems. Sediment and water will inevitably collect at the bottom of the tank, so a fuel pick-up pipe a short distance above the bottom of the tank will, hopefully, prevent water or particles being drawn up into the fuel delivery mechanism. It is vitally important to keep tanks clean. Taking regular samples from the bottom of the tank will quickly tell you if any sediment or water is present and a drain at the lowest part of the tank will simplify this. If this is not possible because of design or location, then use a pump to take a test sample. To be really sure, drain the tank (do this after you have used most of the fuel anyway). Once the tank is empty, open the inspection port and take a good look around. No, mine is not easy to get at either, so I lower a small light into the tank through the internal filler and look around as best I can.

While we try to keep water out at source there is still moisture available from the atmosphere. This condenses onto the fuel tank walls and, being denser than diesel, settles to the bottom. This is unavoidable, so a good primary filter that collects water into a glass bowl as well as trapping particulate matter in a paper element will both clean the fuel and allow you to monitor its quality.

There is yet another problem particular to diesel fuel. Microbes (fungi, bacteria and yeast particles) which float around in the air can get into our fuel at any one of the links in the delivery chain. Once they get into the fuel tank they can react with any water that happens to be there and will reproduce rapidly by cell division. They go particularly well in areas with high relative humidity and a temperature range of 15 to 40 degrees C. After the microbes feast, they accumulate at the bottom of the tank, producing a semi-solid rubbery slime that can be any colour from khaki through to dark grey or black.

Removing it mechanically

Once you have the fuel sludge in your tank, simply treating it with a diesel fuel additive (biocide) may kill the bug but does nothing to get rid of the sediment. The only sure way to achieve this is to remove it mechanically. Drain all fuel, sludge, water and other contaminants from the tank. Scrub it and flush fuel lines and other components in the system with clean fuel to remove any bugs that may be present in other parts of the fuel system. If the tank can be removed, steam-cleaning may be a better option before scrubbing with methylated spirits. Heat will dislodge and kill the bug and the alcohol will both sterilise the tank and dissolve any water left after cleaning. Thoroughly drain the tank and all lines. Only when it is clean, add a biocide to the new fuel and refill the tank. Be careful because both biocide and fuel are bad for our health. Wear hardy rubber gloves and do not breathe any vapours. Dispose of all rags ashore after use. If you store fuel in a jerry can, then clean this and treat it with a biocide as well. It will be difficult to remove all contaminants, so check the filters and change them at the first indication of dirt build-up, then as recommended by the service manual.

Diesel fuels have a higher flash point than petrol. This means it needs a much higher temperature than petrol before it can evaporate; 61 degrees C for diesel (while petrol will evaporate below -40 Degrees C) making the fuel safer to use on a boat. Diesel fuel contains waxes which are an integral part of the fuel, but at low temperatures they can solidify. To minimise the effect of this, refiners make up fuel batches to suit specific locations and seasons. For example, a fuel mix designed for use in Adelaide in the middle of summer will have a different composition to one destined for use in Hobart in mid-winter. The fuel you loaded in Adelaide in summer could solidify or at least thicken if transported to Hobart (in the boat tank or jerry can) in mid-winter; just another reason for not hoarding fuel any longer than absolutely necessary.

Governments are now mandating bio fuels to reduce our dependency on imported petroleum and to care for the environment. Bio diesel is made by blending locally grown animal fat or vegetable oil with the raw petroleum before refining it into fuel suitable for our boats. The amount of bio-additive is usually determined by government mandate and is denoted by a B number. For example, a B5 mix contains five percent of bio material added to the petroleum fuel before refining. In fact, some of the diesel fuel we buy now has a small component (up to two percent) of animal or plant oil. Bio diesel has been around for ages and while it has been proven to not cause problems to engines, because of the nature of some of the by-products of the bio-additive, it may attack natural rubbers which can absorb the fuel and soften. It can also attack copper, zinc, brass, bronze and lead, some paints and wooden decks, especially the caulking on teak decks. However, despite all of this, there is little difference to engine performance and power output with blends of about five percent.

Petrol

This is a dangerous fuel and must be treated with the utmost respect. It has a low flash point so evaporates quickly. Safe storage on board requires that petrol is kept in lockers in approved containers that are isolated from the interior of the boat (they must drain out to the atmosphere). Petrol vapour is denser than air and will ignite readily in low concentration, between two percent and eight percent volume in air, needing only the smallest spark to trigger an explosion. It is most dangerous when pouring. Store only enough petrol to satisfy your immediate needs to minimise the risk of explosion and fire. If you have a petrol inboard motor, then shut it down while filling, ventilate the bilge before starting and be aware of all safety precautions. Remember that the boat alongside can provide both the fuel and the ignition source because the vapour will drift downwind. A vapour alarm is useful, but there is no substitute for a good sniff before starting up. Regularly inspect the whole fuel line. Check for any leaks, corrosion or abrasion, and pay particular attention to joins.

Petrol as it ages

Petrol consists of a blend of highly volatile components. Some of these will inevitably evaporate while petrol is stored (either in a can or in the fuel tank). This reduces the petrol’s volatility, making the engine more difficult to start and also lose power once running. Varnish-like deposits can often form, especially in carburetors, where they may clog needle valves. Injectors can also be affected in a variety of ways. Old petrol may darken in colour, but by this stage it is usually too late to save. Hotter weather will cause it to deteriorate more quickly.

A survey of fuel and engine experts suggests that all fuels should be used as quickly as possible, but in any case not more than 6 to 12 months; less if not kept cool and stored carefully. If you use petrol slowly, top up with fresh fuel frequently rather than leaving it until the tank is completely empty. Some small engine mechanics I spoke to recommend not draining fuel from the carburetors because there is the potential for diaphragms and gaskets to dry out, but others prefer to drain them. Check with your engine supplier and follow their advice; at least if something goes wrong you have a point of discussion. Fuel manufacturers and mechanics recommend not using alcohol-mix petrol in marine applications. Alcohol (ethanol) has a strong affinity with water and will absorb any that gets into the fuel tank. If it absorbs too much water it will settle to the bottom of the tank, called phase separation, and will cause the engine to lose power or become difficult to start. It can also accelerate deterioration of gaskets, grommets, fuel lines, etc, if they are not specifically designed for this fuel.

Remember that fuels are dangerous; they are all designed to burn. Store them with care and do not store more than is necessary for the immediate need. Only use containers specifically designed to carry fuel. Check they have the Australian standards approval number AS2906 affixed.

SIGNS YOUR FUEL MAY HAVE BEEN CONTAMINATED

Fueltreat Australia Pty Ltd, a Melbourne company specialising in fuel storage and treatment, advises that if you have experienced any of the problems below you may have contaminated fuel:

• Hazy fuel due to water “held” up in fuel phase. Inspect the fuel regularly. It should be clear and bright.

• Damage to injectors and fuel pumps.

• Corrosion of fuel system components and storage tanks.

• Having to change filters frequently or finding black slime on filters or in the bottom of the tank.

• Do not use products that disperse or take-up water into the fuel. In fact, such additives can take fuel out of specification.

FILING JERRY CANS

• Do not smoke while handling fuel.

• Place cans on the ground to earth them; do not fill them in the vehicle.

• Touch a metal part of the car to discharge yourself before filling.

• Touch the fuel nozzle onto the lip of the can — this ensures there is no static buildup while filling.

• Fill slowly to reduce static.

• Do not use a plastic funnel because this can insulate the can from the filler nozzle and increase the possibility of ignition.

• Fasten the cap securely before moving.

• Wipe up any spills and dispose of the rag or paper towel safely (do not store it on board). Petrol will evaporate from the rag, increasing the chance of an explosion; oil in the rag can increase the risk of spontaneous combustion.

• Authorities recommend not using a mobile phone or other radios while filling.

MINIMISING DIESEL CONTAMINATION

*  Keep the fuel tank full, especially if not using the boat for some time, because this can minimise condensation.

*  Regularly sample fuel from the bottom of the tank; use the pump if there is no drain tap. Check with a water-detecting paste if it is difficult to drain the tank.

*  Always use a water separating filter and check it regularly.

*  Avoid filling the tank during rain and make sure the deck filter O-ring is in good condition.

*  Always buy fuel from reputable suppliers with a high turnover (truck stops or fishing fleets) because the fuel is likely to be fresher.

* Try to avoid filling just after the supplier has received a bulk delivery because this may have stirred up sediment from the bottom of the tank.

* Use a biocide or fuel stabiliser to treat fuel that will not be used immediately.