AUTOMOTIVE ENGINE LUBRICATION BASICS
by Lance Wright

The engine lubrication system includes the lubricating oil, oil pump, oil filter and the oil passages. Oil lubrication provides a barrier between rotating engine parts to prevent damage by friction, damge which can result in huge auto repair bills. The engine oil provides a method of cooling engine parts that are not cooled by the engine cooling system. Engine oil helps to protect engine components from corrosion by neutralizing harmful chemicals that are the by-product of combustion.

To protect moving parts and reduce friction, automotive engine oil provides a barrier between the rotating or moving engine components. Ideally, a film of oil should exist between moving components. This is called full film lubrication. In order to achieve full film lubrication, a constant supply of clean oil is required. The engine oil system constantly filters and circulates engine oil to ensure that all components are protected.

The engine oil is stored in the crankcase. Most engines hold between 4 to 6 quarts of oil. The engine oil pump pressurizes and circulates the engine oil. The oil will flow from the pump to the oil filter, where it is cleaned. The cleaned engine oil then moves through passages, into the crankshaft where it circulates through the engine bearings. The crankshaft has passages bored into it that allows oil to travel to all the bearing surfaces. The cylinder walls and pistons are lubricated by the oil that is thrown from the crankshaft as it rotates. This is sometimes referred to as splash lubrication. Engine oil will leave the crankshaft, usually at a passage in one of the main bearings and is fed to the camshaft and lifters. On some overhead valve engines, oil will travel through the pushrods up to the valve train to lubricate the rocker arms. Other designs use a passage to feed oil through a rocker arm shaft to achieve the same purpose. The oil then returns to the crankcase by return holes in the cylinder heads. It is then picked up by the oil pump to be circulated again.

OIL PUMP
The engine oil pump circulates and pressurizes the engine oil. It is generally located in the crankcase and driven indirectly by the camshaft. Oil enters the pump via a tube that extends into the bottom of the oil pan. This is called the pick up tube. There is a screen attached to the pick up tube to prevent large particles from entering the oil pump and damaging it. Most oil pumps use rotating gears to pressurize and circulate the engine oil. As oil enters the pump, it is trapped between the rotating gears and forced out at pressure. Some oil pumps use a rotor design which is more difficult to repair and/or rebuild. They are driven in the same manner as the gear pump. This pump uses an inner and outer rotor. Oil is pressurized when it is compressed between the two rotors. Oil pressure is controlled by a pressure relief valve that can be located in the oil pump or near the oil filter.

There are many factors that can affect oil pressure. Internal automotive engine wear such as worn crankshaft bearings, can cause low oil pressure due to the excess oil required to fill the gap between bearing surface and mating component. Oil contamination and dilution from another substance can affect oil pressure. High oil pressure can usually be attributed to a sticking pressure relief valve. Engine oil pressure should always be verified using a test oil pressure gauge. Readings from the vehicles dash gauge can be inaccurate or faulty.

OIL FILTER
The normal circulation of motor oil through the engine lubrication system, results in the accumulation of particles in the motor oil. These particles can consist of dirt, rust and material generated from engine wear. During engine operation, the normal path for the circulation of oil is from the oil pump to the oil filter, then on to the crankshaft bearings. If particles were to become embedded in the soft material used in the crankshaft bearings, a barrier to lubrication can occur and cause excessive wear in the bearing material or the crankshaft surface. Therefore, in order to avoid future costly auto repair jobs, it’s best to buy a top oil filter and replace it regularly.

Most vehicles use a full flow oil filtration system. This is a system in which the oil must pass through the oil filter in order to circulate through the rest of the engine. The full flow oil filter system allows better engine protection due to a more complete filtration of the motor oil.

The spin on oil filter cartridge is constructed of a metal outer canister. The top of the oil filter contains a seal and the inlet and outlet passages for motor oil. The oil filter contains a filtering element that traps and stores particles. The filter element usually is constructed of pleated paper. The filter element is rated by the minimum size of the particles it can trap. This is measured in microns.

After extended use, the filter may become saturated with particles, limiting the ability of the oil filter to adequately clean the automotive engine oil. Engine oil flow may become restricted in severe cases. The excess oil pressure resulting from this blockage can cause the engine oil system to bypass the oil filter. Servicing the oil filter at regular intervals is highly recommended to properly maintain and protect an engine and thus avoid unnecessary auto repairs.

ENGINE OIL
Automotive engine oil is a blend of refined petroleum and additives. Its main purpose is to reduce or prevent wear of moving components. Motor oil accomplishes this by providing a barrier between moving components. Motor oil is also used to cool certain engine internal components.

Motor oil is rated by the SAE by viscosity and service rating. Viscosity is the ability of oil to flow at a given temperature. Multi viscosity oils are recommended by most automobile manufacturers today. Multi viscosity type engine oil has the ability to provide good flow during cold temperatures without breaking down at high temperatures. A typical multi viscosity motor oil is 10W-30. The 10W is winter rating for the engine oil. The 30, is the characteristic of the oil at 100∞C. This oil can be considered a 10W oil that behaves like a 30 at 100∞C.

Multi viscosity oils are made possible by the use of complex polymers. A manufacturer will use light base oil and blend it with polymers. During cold temperatures, the polymers will become coiled up in the oil, allowing it to maintain the characteristics of the base oil. As the engine warms up, the polymers unwind causing the oil to resist thinning. The polymers help the engine oil to achieve higher weight characteristics at 100C.

(Lance owned his own auto repair shop for 30 years before retiring in 2006.)