Air Leaks in Diesel Engines

Air Leaks


Where do they come from?

Besides the problems of fuel contaminated with sludge, microbes and water, there is another common problem that affects the diesel engine; Air leaks. This is air entering the fuel system through fuel lines, connections, the primary filter and the engine fuel system. Most air leaks happen between the filter inlet and the engine lift pump. When the engine is operating the lift pump creates a vacuum to pull the fuel through the filter to the engine. As the filter starts to clog this vacuum will also increase. Air enters the fuel system thru loose or compromised connections. Depending if the engine is a self bleeding type or not will determine when the engine will shut down due to a lack of fuel. The normal complaint for this problem will be that the engine will run for a given time, the RPMs will surge and then the engine will shut down. The operator will bleed the engine, then restart the engine and all goes well until the problem repeats again. Engine shut downs can create a dangerous situation when having to navigate in tight areas or poor sea conditions.

A simple way to troubleshoot the system is to install a vacuum gage between the filter and the engine lift pump, and a shut off valve on the inlet of the filter. Perform a test that we call the operational test or pre departure check, start the engine and let it warm up, shut off the fuel supply to the primary filter and let the vacuum gage increase to around 10″hg, now shut down the engine and watch the vacuum gage to see if the needle has changed after 5 to ten minutes. If the needle stands at the reading it was when the engine was shut down then the system is tight. If the vacuum gage needle moves towards zero, there is most likely a leak at one of the connections. Now if you want to check the fuel system from the fuel tank to the engine do the same test but shut off the fuel at the tank shut off.  The most common areas for trouble are at the engine connections where there is a high amount of heat, vibration, and/or hose barb type connections. The fuel filter is an another area that must be checked for rolled o rings, loose fittings or valves. Always check any pipe thread connection for proper thread sealant (not thread tape).

The vacuum gage is a very important tool to have onboard your vessel. It allows the operator to monitor the online filter so you know when to change the filter and allows the system to be checked before leaving the dock on a trip or after having maintenance performed. As a complete fuel maintenance system our FilterBOSS COMMANDER units come standard with a vacuum gage. Along with our patented dual filter controller system, our remote Early Warning System (EWS) at the helm and an integrated onboard fuel polishing system, you are sure to have the best protection for your boat. We also offer an Early Warning system kit for single filter installations. Remember it’s easier to fix it at the dock then at sea.   Andy

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