When burning the hydrocarbon fuel leaves materials and products that one of the most important is water. If the engine is hot, produced waters exit as vapor from the exhaust. However, if the engine is cold, water vapors due to the condensation may come in liquid, found its way into the engine and mixed with oil. Idle of engine and moving at short distances makes the engine doesn't find enough time to get warm. Under these conditions generated a significant amount of water that by combustion compressed and come in to cylinder and sits on the cylinder walls and finally by entrance gases passes from rings and come in to carter. The presence of water in the oil, especially in carter and elsewhere that oil temperature is low, causes formation of soft and sticky sludge.
Also, when fuel comes in to carter, the value of the combustion products carry out to carter. Such substances contain solid residues, soot and may lead-containing compounds. With warming the engine evaporates the oil of carter but remains solid materials in oil and as a result the sludge is produced in carter. So mixture of water, oil, fuel and other pollutants resulting from combustion can be arrived to carter and converted to sludge.
Of course the high compression ratio of diesel engines isn't very sensitive towards of sediment formation in combustion chamber. If these deposits in gasoline engines are constantly exposed to the combustion process may be red and source spark to ignite the fuel in the combustion chamber which results in undesirable phenomena such as strike, pre-ignition and abnormal noise in the engine. Used of fuel with high octane number and oil that is resistant to the formation of sediments and sludge to reduce these phenomena. Since the formation of sediment and sludge are causes of erosion in the engine and lack of suitable lubrication, the engine oil should be changed according to a good program. Of course, other factors may have an impact on engine failure by oil. For example, the presence of even small amounts of antifreeze to the oil can cause irreparable damage to engine parts. To find the presence of glycol antifreezes in the oil, the best method is colorimetric chemical method. If small amount of sodium is in the oil, indicates anti-freeze entered to oil. However sodium may also be present in some additives that should be noted.