How an Engine's Lubrication System Works

Purpose Of Lubricating System

The lubricating oil performs the following functions in an engine:

• The oil lubricates moving parts to minimize wear by sealing the clearances between moving parts such as bearings, shafts, etc. Thus, the parts move on layers of oil, and not in direct contact with each other, which reduces power loss in the engine.

• The oil obtains heat from the moving parts of the engine which is transferred into the cooler oil in the oil pan. Therefore, the oil performs the function of a cooling agent. Some engines have oil nozzles which spray oil at the underside of the pistons, thereby removing heat from the pistons.

• The oil fills the clearances between rotating journals and the bearings. When heavy loads are abruptly placed on the bearings, the oil acts as a cushioning agent, which reduces the wear on bearings.

• The oil creates a seal between the walls of the cylinder and the piston rings, thereby reducing exhaust gas blowby.

• The oil performs the function of a cleaning agent by picking up dirt particles and taking them to oil pan. Larger particles are retained at the bottom while smaller particles are filtered out by oil filters.

Parts And Operation Of Lubricating System

• Oil Pump: The gear-type oil pump has a pair of meshing gears. The spaces between the teeth are filled with oil when the gears unmesh. The oil pump obtains oil from the oil pan and sends oil through the oil filter to the oil galleries and main bearings. Some oil passes from the holes in the crankshaft to the rod bearings. Main bearings and rod bearings are lubricated adequately to achieve their desired objectives. In the rotor type oil pump, the inner rotor is driven and drives the outer rotor. As the rotor revolves, the gaps between the lobes are filled with oil. When the lobes of the inner rotor move into the gaps in the outer rotor, oil is forced out through the outlet of pump. An oil pump can also be driven by a camshaft gear that drives the ignition distributor or by the crankshaft.

• Oil Pan: Oil also flows to the cylinder head through drilled passages that make up the oil gallery, lubricates camshaft bearings and valves, and then returns to oil pan. Some engines have grooves or holes in connecting rods, which provide extra lubrication to pistons and walls of cylinders.

• Oil Cooler: Oil cooler prevents overheating of oil, by flow of engine coolant past tubes carrying hot oil. The coolant picks excess heat and carries it to the radiator.

• Oil Filter: The oil from oil pump flows through oil filter before reaching the engine bearings. The oil filter retains the dirt particles and allows only clean filtered oil to pass.

Lubricating System Indicators

There are indicator lights which are “on” when the engine oil pressure is low. Electric analog and electronic digital gauges are used to indicate the oil pressure. A dipstick is used to measure the oil level in the oil pan, while in some vehicles oil change indicator lights are used to identify the quality of oil.