What do fuel filters do?
Fuel filters remove contaminants and debris from the fuel before the fuel moves into the engine. Having clean fuel is imperative in keeping your overall fuel system healthy. When debris or other contaminants manage to make it past a fuel filter, everything in the fuel system, including fuel injectors, fuel injection pumps and common rail sensors & controls, can become clogged or damaged. The result is improper fuel injection, poor performance, or even total engine shut down.
PRIMARY FUEL FILTER
Spin on fuel filter cartridges or “drop-in” elements, are what do the work in the fuel filters. The primary filter or element is placed in a tube, where suction pulls from the engine, drawing fuel from the outside of the element into the center. Particulate, typically in the 10 to 30 micron range, is trapped in the primary fuel filter. Simultaneously, heavy contaminants and water that may be present are spun through a centrifugal (centrifuge) action and emptied into a filter bowl (also known as a water trap).
This filter bowl is oftentimes clear (like on a Racor filter) but on classed vessels such as military and maritime vessels the bowls are solid (shatter/flame proof). The primary filter bowl should be inspected as part of your “pre-check” of the engine room. If your filter bowls are not visible, you can open the bottom valve or drain plug and release a bit of fluid from the primary filter into a cup or container to visibly check for water or debris. It is normal to have a small amount of debris in the primary filter. If you do see a lot of water or debris in the primary filters, consult with a fuel polishing company or contact your engine servicing dealer. Do not continue to operate the engine if you suspect something is amiss.
SECONDARY FUEL FILTER
The secondary fuel filter is attached to the engine because this fuel filter, unlike its cousin (primary), is pressurized by the diesel engines’ low-pressure supply system. Secondary fuel filters can be either a spin on filter or cartridge (drop-in) type. The secondary fuel filter traps smaller particulate normally ¼ the size of what the primary fuel filter handles. Typical secondary fuel filter size is in the 2.5 to 5 micron range. Sometimes the secondary fuel filter has a water blocking membrane that will reduce or stop fuel flow to the engine.
We’ve experienced this reduction of fuel flow with fuel filters having less than 25 operating hours on them! After the fuel is filtered by the secondary fuel filter(s) it goes to the inlet side of the high pressure or injection pump. Some engine manufacturers will install an inlet screen as a “last effort” of keeping debris from entering the high-pressure fuel system. Manufacturers will also sometimes install a pre-filter before the engine supply pump as well. MAN has prefilters to trap particulate on the inlet side of the engine and MAN common rail engines are equipped with a screen on the inlet side of the high-pressure pump. If that guy gets clogged, you may see an alarm pop up on your display.
How often should I change my fuel filters?
Fuel filters are typically ready to be changed every 200-300 running hours or once a year. If the fuel quality is suspicious or if you are seeing more debris in the primary filters than normal, you should change the fuel filters at half the normal interval above. Many times, Scott Marine Power will suggest changing fuel filters more often if the engines are losing power or if there is a fuel system related alarm accompanying poor performance.
What kind of fuel filters do I need?
The current industry standard in the US are Racor by Parker Hannifin. Separ primary fuel filters are also popular, especially in European vessels, and are available locally in Fort Lauderdale. Scott Marine Power sells both brands of these primary filters as they can handle the engines’ fuel flow at full throttle- an important factor to consider when choosing a filter.
Once you know what brand of filter you have, the next step is choosing the size for installation of your primary filter. 10 micron is smaller than 30 micron but your engine’s specific fuel flow requirement will determine what micron you’ll need. Refer to the recommendations by your engine manufacturer or engine dealer. If you are still unsure of what filters or cartridges to use, give us a call and we would be happy to walk you through your choices!
Conclusion: Believe it or not that there is a lot more to the fuel system than what we mentioned in this short overview. Diesel fuel is inherently much different than other fuels and therefore its characteristics are very different. Because diesel is unique, it requires special service and maintenance!
How else can I maintain a healthy fuel system?
While changing your filters is an extremely important part of keeping everything in your vessel running smoothly, there are a few other tips to getting the most out of your fuel system. These include...
- Using your boat regularly to keep fuel from going stale.
- Refueling at reputable filling vendors!
- Adding a fuel stabilizer to keep your fuel fresh.
- Installing a vacuum gauge to check your primary fuel filter condition.
- Calling Scott Marine Power to service your vessel’s fuel system!