Motor oil contamination causes deterioration of oil. Some of the more common contaminant sources include dirt, sand and dust from the air, soot, unburned fuel in the oil, water from condensation of the combustion process, wear metal particulates that the oil filter cannot trap and hold, corrosion by-products and additive elements that have degraded. As dirt, sand and dust continue to enter the engine; they combine with other contaminants and cause more damage than they would separately.

One of the many by-products of combustion is soot. Soot is created by incomplete combustion of fuel in the combustion chamber. The high temperature and pressure cause particulates to stick to each other and become trapped by the oil which transports these particles into the engine oil sump. In the sump, these particulates cling to internal parts of the engine or are carried out of the oil system into the fuel system by the oil system vent. Soot can be highly abrasive as well as cause filters to become filled and or plugged in extreme cases. Most small engines do not have an oil filter, so these contaminants remain in the oil accelerating the buildup of acids.

Acidic by-products of combustion, which can produce a highly corrosive mixture and cause corrosion and pitting of internal engine components and additional generation of wear debris. These same acidic solutions can also mix with any water inside the engine and form an emulsion that can cause problems with oil filters and oil passageways. For this reason, J & L Industries recommends you change your outdoor engine oil before you store your equipment for the winter.