Diesel Fuel Filters

Diesel Fuel Filters Choose Your Filters Carefully and Install Them Yourself. Your Engine Will Reward You. By Paul Esterle Updated June 23, 2009 Diesel engines are relatively simple devices. They only require three things: clean air, clean oil and clean fuel. On a boat, clean air is easy, just keep the air filter clean and you're good. Clean oil is slightly more difficult, but as long as you follow the manufacturers' suggested oil change schedule, it too can be had. It is the need for clean fuel where things start to get dicey. Depending on the source of the fuel and your storage arrangements, diesel fuel can be infiltrated by water, particulates and various chemical contaminates. Water, in particular, can be very damaging to the precision fuel management components in a diesel engine. Under the typical pressures used in diesel fuel pumps and injectors, water can actually act as an abrasive, quickly wearing down components. And so, every engine has a filtration system to combat contamination. Note that I said "system," because proper and effective fuel filtration should include two types of fuel filters: a primary filter and a secondary filter.

RACORThe Racor 120 is a widely used spin-on element fuel filter.Installing a diesel fuel filter is easily done by the average boater. But you must take your time and do your homework. This is, after all, your fuel system – an organ your engine cannot run without. Do it right, however, and your engine will be easier to service and run more reliably. FILTER BASICS

Most diesel engines come equipped with a secondary filter as part of the enginemounted fuel delivery system. This on-engine filter is most often rated at two microns (see graphic). This is sufficient to remove hard particles that can damage precision fuel delivery components. However, a secondary filter typically does not usually remove water from the fuel. That job is handled by a primary filter, which is usually added by the boat builder or engine installer between the tanks and the engine. If your boat lacks a basic two-filter system, you can install new filters easily – and you should. Single-filter systems are much more prone to clog and lose effectiveness. Diesel fuel filters can be divided roughly into two groups"” spin-on or drop-in. Spin-on fuel filters utilize a paper element to strain fuel, which is then encased in a metallic case, similar to an oil filter. These filters screw onto a bracket and have a separate bottom bowl that screws onto the filter unit. This style of filter is usually relegated to lower capacity applications (capacity is rated in Gallons Per Hour, or GPH). One popular diesel filter is the Racor model 120RMAM. This filter is available with spin-on elements of either two microns or 30 microns (the 30 micron is used for primary filtration). This unit is rated at 15 GPH. It has a metal bowl and requires only 2-inches of service clearance underneath the unit for removing the spin-on filter element. It has two inlet and two outlet ports, to accommodate multiple tanks and engines, or inlets and outlets can be plugged for use in a single-engine or single-tank installations. The filter is less than 6-inches high and 4-inches wide, allowing a compact installation. Drop-in element filters have a housing that can be opened up to receive a separate drop-in element. These filters usually accommodate higher capacity than spin-on filters. One example of a widely-used drop-in element filter is the Racor 500FG. This filter is rated at 60 GPH with a 10 micron element. This filter is much larger than the spin-on type, at 11.5-inches high and 5.8-inches wide. The inlet and outlet ports are also larger, at ¾-16 UNF. You will also need more room under the filter unit for maintenance, 4 inches in this case. This unit is also available in a dual filter setup, the 75/500FGX.

SYSTEM CONFIGURATIONS Most primary filters are installed on the vacuum side of the fuel pump. Vacuum gauges are also sometimes installed to gauge the health of the primary filter. When the vacuum gauge rises to a given level, it is time to change filters. A filter change can result in some additional problems when air is induced into the lines, requiring the dreaded "bleed" of the fuel system. To avoid this, new filters should be filled with clean diesel before being installed. In fact, many drop-in element filters have ports on the top of the filter to pre-fill the assembly. This helps reduce the chances of getting air into the fuel system – and the need to bleed. You can also minimize the chance of getting air in your fuel lines and make filter maintenance much easier by installing dual filters and plumbing that allows you to isolate each filter. In this arrangement, a two-way valve allows you to switch from the clogged filter to a new filter. The clogged filter then can be changed out while the engine is still running. Many filter manufacturers, including Racor, offer these units pre-plumbed, though they can be expensive. Typically, the two filters are mounted side-by-side on a metal mounting bracket, with the filter selector valve between the two. Another option is to create the system yourself, creating a plumbing scheme with a bypass feature that will allow you to switch the filter out of the fuel line. It requires three on-off fuel valves and some extra plumbing, but the price is much more reasonable than a preassembled commercial unit. The system has an on-off fuel valve before and after the filter unit. A bypass fuel line with another on-off valve is installed before the first valve and after the second valve (see graphic). By closing the valves before and after the filter and opening the valve in the bypass line, the fuel will flow around and the filter. After changing out the filter element, you open the two valves in the main line and close the bypass valve, putting the filter back on line. If the stars are aligned and your luck holds, bleeding the engine won't be necessary. You take a slight chance

running on bad fuel while the filter is changed, but the secondary filter should still protect the engine – and the cost savings is substantial.

RACORThe Racor 500 series is a popular drop-in fuel filter.In addition to the vacuum gauges, several other filter options are available. Water probes can be installed in some filters, as can manual fuel pumps to make bleeding the filter and engine easier. Some diesel fuel filters are available with an optional see-through bowl on the bottom. This makes it easy to inspect the quality of the fuel and drain off any water using the fuel drain on the bottom of the bowl. However, a little-known ABYC (American Boat and Yacht Council) standard requires any fuel filter installed in an engine space have a fire rating. This requires a metallic bowl or bowl protector. A standard option in Racor filter elements is something called Aquabloc. This is a chemical treatment for the element paper that keeps water from passing through the filter. This water then drops down to the filter bowl where it can be drained. The one caveat with this treatment is that the effective life for the treatment is one year, after which its effectiveness falls off. INSTALLATION CONSIDERATIONS Once you have decided on the rating of your primary filter (10, 20 or 30 microns), your next decision is the size of the filter in GPH. Most engine manuals will provide a fuel consumption curve or maximum fuel consumption figure. If not, you can roughly estimate the fuel consumption of your engine by using the formula: Gallons Per Hour = Horsepower (max) x 0.18 In other words, maximum fuel consumption in GPH is 18 percent of the maximum horsepower rating. Proper sizing is important because many diesels pump much more fuel than is actually consumed. That additional fuel is used to cool parts of the fuel system

and to insure sufficient fuel is present for throttle increases without any lag. The excess fuel is then returned to the tank. Unless properly rated, filters should be installed outside of the engine or generator space. Size-up the hose requirements before starting any installation. Check the routing of each hose to avoid any hot spots or areas where the hose may rub or chafe. Plan on supporting the hose every 18 inches or so to avoid any unnecessary flexing or rubbing. Resist the temptation to increase the size of the fuel line; a larger fuel line means an increase in the weight of the fuel to be pumped and may overtax the fuel pump. Pay particular attention to the size and style of the hose connections. Most filters come with female NPT ports into which you can screw different fittings. Never use Teflon plumbers tape when installing these fittings. Use a thread sealant instead.

RACORThis is an example of a pre-packaged dual filter unit.In some cases, standard barbed fittings and hose clamps are used. In many larger installations, specialized hose ends and fittings are required. In all installations, do not assume that fittings are compatible. For example, JIC fittings are machined with a 37-degree bevel on the sealing end. SAE fittings, on the other hand, have a 45-degree bevel, so the two are definitely not interchangeable. If you don't know exactly what type of fitting is used, take a sample hose to a local chandlery or diesel shop and have them identify it. If your installation will require hoses be made up at an outside shop, spend the time to properly – and definitively – determine the hose path and lengths. Having to leave the boat to have a hose re-made will be more time consuming than measuring twice. ROOM TO WORK It sounds elemental, but make sure there is enough clearance and access to properly service the filter. There should be plenty of room above the filter if you are using a drop-in filter, and room below to place an appropriate sized container to control any drips or spills.

Your filters will also need an adequate surface for mounting. A filter full of fuel represents a considerable amount of weight, and that can stress weak bulkheads. Use thru-bolts and locking nuts for security. One of the most critical steps in installing a filter is eliminating leaks. On the suction side, air will leak into the fuel system, making successful bleeding problematic. This is why plumbers putty or thread compound, such as Permatex Pipe Joint Compound, is used, rather than Teflon plumbing tape. While the suction side of the system is the usual location for a primary filter installation, you can also install a filter on the pressure side of the pump. But the maximum allowable pressure and fuel flow ratings for the filter must be well above the fuel pump pressure and flow. The downside of this location is that the pressure, coupled with the need for more connections, can result in an increased chance of fuel leaks. While on the suction side, air will leak into the system, on the pressure side, fuel will leak out of the system – and under pressure at that. No matter where you locate your filters, make sure you change them regularly. Check the filters evey time you check engine fluids. By monitoring the pressure gauges (for systems on the vacuum side), you can see when filters need changing. Carry several spares and change at the first sign of trouble, making sure to fill the unit with fuel to eliminate the need to bleed. Your engine will thank you