How to Filter Diesel

Diesel engines use a fuel that contains gasoline mixed with oil. The oil serves as both coolant and lubricant. This self-lubricating design makes diesel engines very durable, but they are also very easily affected by contaminants in fuel. The fuel pump that lies at the heart of a diesel engine operates at very high pressures, and will not function with even a small amount of grit inside it. For this reason, diesel fuel must be filtered before it reaches the engine. This happens in several stages.

• 1

  Filter the fuel as you pour it into the gas tank using a filter funnel. As of November 2010, these funnels range in price from $6 to $200, but some of the funnels at the lower end of that range did an acceptable job of filtering grit out of diesel fuel. To use these filters, simply insert the narrow end into your fuel tank and pour the diesel from the pump slowly enough to avoid overloading the filter.

• 2

  Use your engine's fuel filters. Diesel engines include fuel filters between the tank and the engine. All engines have a primary filter on the suction side of the fuel pump with holes 10 to 30 microns wide; this catches grit in the fuel from the tank and prevents the secondary filter (if there is one) from clogging. Secondary filters are mounted between the fuel pump and the fuel injectors and are much finer, with holes between 2 and 10 microns wide. These filters must all be cleaned regularly to work properly.

• 3

  Filter water from your engine with its fuel/water separator. This is a component built into the engine that removes water that would otherwise cause rust and damage to the interior of the engine. It does so by using specially treated water-repellent paper to force water to the bottom of a storage tank. This tank must be regularly drained for this system to keep working.

• 4

  Filter fuel before putting it in your tank. If you are making biodiesel at home from cooking oil or plant products, this will be necessary. Pour the diesel through polypropylene bag filters, available from water filtration suppliers. The fuel can first be poured through a wide (25-micron) filter, then through 10-micron, and 5-micron filters. This will keep the finer filters from clogging.