Crankcase dilution is a phenomenon of internal combustion engines in which unburned diesel or gasoline accumulates in the crankcase. Excessively rich fuel mixture or incomplete combustion allows a certain amount of fuel to pass down between the pistons and cylinder walls and dilute the engine oil. It is more common in situations where fuel is injected at a very high pressure, such as in a direct-injected diesel engine. When a mixture of air and fuel enters the cylinder of an engine, it is entirely possible for condensation of fuel to occur on the cooler parts of the cylinders. The condensate may wash the lubricating oil from the cylinder walls, travel past the piston rings and collect in the oil pan, thus increasing wear and also diluting the lubricating oil. Since the less volatile components of the fuel will have the greatest tendency to condense, the degree of crankcase-oil dilution is directly related to the end volatility temperatures of the mixture. Causes Crankcase dilution occurs when the fuel oil from the engine gets into the lube oil of the engine. This can be caused by the walls being wetted due to the fuel condensing in the cylinder. If the engine is cold, or there is an excess amount of cooling around the cylinder, the fuel oil will condense and have a higher chance to end up in the crankcase. Another way that the fuel oil can end up in the crankcase is because there is too much wear on the piston compression rings. The job of the piston compression ring is to keep the oil and the exhaust gases from entering the crankcase, but when there is too much wear it can no longer do its job. Other than the piston rings, “blow-by” gases can push the fuel oil past the rings and into the crankcase. “Blow-by” gases are a mix of fuel oil and exhaust gases that push past the piston rings. Crankcase dilution is caused more when the lube oil is fresher. Another cause of crankcase dilution is a slow or delayed injection cycle. This causes the timing to be thrown off and the oil is most likely to enter the crankcase at this point. Water and dirt can also further the effects of crankcase dilution. Also, soot getting into the lube oil can cause crankcase dilution, but there are additives that can keep the soot at the top