How many different opinions or recommendations have you heard concerning changing the engine oil. One fact for sure, if the oil is not changed frequently enough it will cause a sludge build up in the engine. Oil change frequency varies depending on the driving conditions. This sludge can cause restrictions in the flow of the engine oil and ultimately damage the engine. The illustrations above are two different engines the black looking pictures are the sludge build up and the lighter is an engine that had more frequent oil changes.