Adding new fluid can be a source of contamination. Even though it’s fresh from the drum, new engine oil isn’t clean. (It may look clean, but, remember, the human eye can only see a particle the size of about 40 μm.) Also, diesel fuel cleanliness varies from pump to pump. Typical fuel cleanliness levels coming out of the pump are ISO rated at 22/21/18. (ISO cleanliness code of 22/21/18 translates to a particle count of 20,000 to 40,000 per millilitre for particles of 4 μm and greater; 10,000 to 20,000 per millilitre for particles of 6 μm and greater; and 1300 to 2500 per millilitre for particles of 14 μm and greater), and water content is typically 200 to 300 ppm. Never assume your fluids are clean until it has been filtered.
Built-in contamination, also called primary contamination, is caused during the manufacture, assembly and testing of the engine and its components. Metal filings, small burrs, dirt or sand and other contaminants are routinely found in initial clean up filtration of newly manufactured engines.
Ingressed or external contamination comes from the environment surrounding the engine or vehicle. Dirt can enter the engine liquid supply through crank case breathers or fuel tank breathers and vents and the air intake system. Ingressed moisture, particularly, can cause longer term problems. As a hot system cools at night, cool moisture-laden air can be drawn into the engine or fuel tank; as the air condenses, water is released into the engine or fuel tank. Water in excess of 0.5% by volume in a hydrocarbon-based fluid accelerates the formation of acids, sludge and oxidation that can attack internal components, cause rust, and adversely affect lubrication properties. The severity of ingression and type of contaminant are dictated by the applications and environment.
Maintenance procedures can introduce contamination into the engine. Opening the engine allows airborne particles to enter. Removing air filters, opening oil caps, fuel tank caps and removal of oil and fuel filters are all possible sources for introducing contamination to an engine. Keep your system closed as much as possible and take care to be sure everything that goes into the engine is as clean as possible. One common example is very often funnels are used fill the engine with oil. The oily funnel will collect dirt between uses. The funnel should be properly cleaned before using it to fill the engine with oil.
The major sources of contamination in the engine are the combustion by-products (soot) and oxidation of the fluids in the engine due to the thermal stressing. Wear-generated contaminants are a hazard during engine operation.
The circuit actually generates additional particles as the fluid comes into contact with the precision machined surfaces of cylinder walls and pistons, injector needles and pistons and crankshaft bearings. Contaminant levels can keep doubling with every new particle generated. The result can be catastrophic if these contaminants are not properly filtered out of the system.
Rubber & Elastomers
Due to temperature, time, and high-velocity fluid streams, rubber compounds and elastomers degrade—thus releasing particulates into the fluid.
Biodiesel can support biological growth and generate organic contamination and microbes.