FILTERS, WATER TRAPS & CLEAN FUEL IN DIESELS BY TERRY BUDDELL

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1 FILTERS, WATER TRAPS & CLEAN FUEL IN DIESELS BY TERRY BUDDELL Let s not beat about the bush, clean water and dirt free diesel fuel is the primary prerequisite for along engine life. Next to oil, clean fuel is the most important element in a modern boat diesel engine. A diesel requires only three things to run perfectly, clean air, clean fuel and clean oil. However, more and more of today s fuel delivered at the marina or service station is likely to be contaminated, sometimes to a high degree! How come? In many ways to be frank. You d be shocked at the complete filth that lies accumulated in many underground storage tanks. A few years ago I went to a talk given by a company called Fuel Doctors, the owner had been in the fuel cleaning business for many years and was contracted to clean out major fuel storage facilities around the country. The several demijohns of various sludged up dirty fuel samples he brought along would truly have been more at home in a sewerage plant than a diesel tank. They were brown, green, solid, slimy and oozing. He showed us photos of his workers wearing full protective clothing knee deep in sludge, shoveling the stuff out! Amazing but true. It is astonishing how hundreds of litres of drain and rain water finds its way into bowser tanks, thence to your boat tanks. When another fuel truck dumps a fresh delivery, it churns up the water and dirt at the bottom. Diesel engines are delicate and a fuel injection pump is a precise and expensive piece of gear. Traces of dirt and water can and will stop it dead in its tracks. It is a total nightmare to have to completely remove water from a fuel system but luckily diesel floats on water. Therefore, most tanks and filters in a boat diesel have water drain taps and cocks at the bottom of them for easy access, making the job easier. Page 1 of 6

2 Water in fuel creates havoc and damage. Misfiring and poor reduced performance are the least of your worries, however it is known that salt water hitting an injector at engine temperatures can blow the tip off an injector after turning to steam and exploding. Raw fuel flows into the cylinder, washes away the oil whilst the broken tip is smashed into the piston and valves several hundred or even thousands of times.ouch. Water in fuel tanks creates another foul and dangerous problem. Live microbes live and breed in the diesel/water mixture known as The Black Death. Their excrement falls to the tank bottom growing deeper until, when stirred up by waves it is sucked in to the delivery pipes and to the filters whereupon it immediately blocks them causing fuel starvation. Biocide treatments are of vital importance to kill the bacteria in the tropical areas where fuel/water mix is warm ideal conditions. Rather than let these awful problems arise it is far better to prevent rather than cure. Check fuel for water at regular intervals with a clear plastic tube from the tank bottom or, regularly drain a sample from the tank. Filter all fuel taken onboard through a fine mesh filter. Fill tanks to the top to prevent condensation. Always add a biocide check which is suitable for your motor. CARE OF FUEL FILTER In most modern diesels the fuel filter setup is of vital importance. It should consist of a primary filter (or several together) and an engine mounted secondary filter. Bear in mind there are several different types but their aim is mutual: to separate the water from the fuel. There are several names that are familiar CAV, WATERSTOP, CAV WATERTRAP, CAV WATERSCAN and so on. Some have an alarm built Page 2 of 6

3 in that alerts the operator to water presence build up in the trap, others have fine grain paper filters that suck the water in like blotting paper which then coalesces (drops get bigger) which roll down to the water trap. These are known as Agglomerator filters. There are various methods of water removal mostly from a drain top on the bottom half of the see-through filter bowl. Naturally it follows that a regular check is paramount and a supply of filters be carried always in case of a sudden clogging of the system. Let me make it clear that primary and secondary filters do not do the same job. The primary filter is the first defence line against water. They are known as sedimenter filters and water and large particles are filtered out. The fuel passes through ten to thirty micron filters (a micron is one millionth of a meter of an inch). Secondary filters are designed to remove very small particles of dirt and water droplets that have passed by the primary filter. They have very fine mesh as opposed to filter papers. Any time a primary filter change is undergone because of severe contamination as opposed to a maintenance change always check the secondary filter meshes too. NOTE: Ensure this operation is done spotlessly, any induced dirt can ruin your injector pump enter BIG BILL! On many vessels a sensible arrangement is to have several primary filters in line and each fitted with a separate on/off cock so the engine may be kept running whilst each of the filters can be changed in turn. Sometimes when clogging occurs, it may still require the motors to run if it happens at sea. The moral of this article is change filters regularly as part of a regular maintenance check. Although robust and strong a diesel engine has its own particular Achilles Heels, one of them is clean, spotlessly Page 3 of 6

4 clean fuel. Even the tiniest dirt particle can score the interiors of lift pumps and injectors and lead to expensive payouts. Finally, bear in mind when changing fuel filters, refill them with fresh fuel before replacing otherwise a massive airlock will happen. Change all O rings in the filter body, they are cheap. Never cross thread the filter, it will leak air forever and keep spares at all times. CHANGING A FUEL FILTER (with replaceable filter) Clean the outside spotlessly. Unscrew the thumbscrew, drain all water and sludge. Unscrew centre bolt holding base and remove. Release filter, check for contamination. Discard filter, check base ring undamaged. Clean the base, bowl and check O rings. Fit new filter, check O rings and base ring square. Seat bowl and base correctly. Tighten centre bolt, don t over tighten! Page 4 of 6

5 Articles on Marine Surveying for This article is copyrighted and is the intellectual property and was written especially for the website of Terry Buddell, Marine Surveyor of Mobile ( 061) It may not be copied, stored in any electronic device without the express permission of the website owner and author, Terry Buddell, Marine Surveyor, Australia Wide Surveys, Queensland. If a copy is required or permission to print please contact arcus1@bigpond.com. Page 5 of 6

6 Articles on Marine Surveying for This article is copyrighted and is the intellectual property and was written especially for the website of Terry Buddell, Marine Surveyor of Mobile ( 061) It may not be copied, stored in any electronic device without the express permission of the website owner and author, Terry Buddell, Marine Surveyor, Australia Wide Surveys, Queensland. If a copy is required or permission to print please contact arcus1@bigpond.com. Page 6 of 6