There are FIVE main functions of lubricants: Reduce Wear: Fluid lubricants maintain a film between parts to reduce friction and prevent surface-to-surface contact. Surface contact causes wear and for the surfaces to weld together. Cool Surfaces: Lubricants remove the heat produced by friction when acting as a heat transfer medium, or coolant. Heat must be removed to prevent damage of other surfaces. Cooling mechanical parts is an important function of any lubricant. Clean Surfaces: Lubricants flush debris from surfaces and carry it away. This can then be filtered out of the lubricant. By carrying away debris, lubricants prevent it from blocking oil passages and damaging parts. Since lubricants are circulated around mechanical parts, they are a logical choice for a cleaning agent. Seal Parts: Fluid lubricants fill open areas between moving surfaces. This provides a SEAL that prevents foreign matter from passing between moving surfaces. Keeps material from getting between surfaces also helps to keep them clean. Cushion Parts: Lubricants provide a cushion against mechanical shock by filling open areas between moving surfaces. Without a lubricant cushion, components could be damaged by mechanical shock and vibrations.