In the modern engine, the lubrication system is more vital than every due to the very low tolerances and higher temperatures that the engines must perform at.
System Components
- Oil pan – holds the oil required for the system, provides a means of draining the oil through the oil plug and houses the oil pump and
pick up tube. - Oil pump – provides a continuous supply of oil at sufficient pressure and quantity to provide adequate lubrication to the entire engine. The pump is driven either by the crankshaft, camshaft, distributor or timing belt.
Pressure regulator – usually an internal part of the oil pump assembly, relieves excess oil pressure by a spring and check valve. - Oil filter – the function of the oil filter is to remove dust, dirt, sludge, and water before it reaches engine parts.
- Oil galleries – passages for oil to flow to various engine parts.
- Oil pressure indicator – gauge or light to indicate oil pressure problems. The indicator is connected electrically to an oil pressure switch or “sending unit”.
- Oil cooler – cools motor oil to reduce oxidation. Not all vehicles are equipped with this item.
- Oil level indicator – also known as dipstick, indicates the level of the oil in the oil pan and sometimes has information such as the type of oil recommended by the manufacturer. Some vehicles have an electronic sensor in the oil pan to indicate low oil levels.
Oil Route
The oil starts in the oil pan where it is drawn up through the pickup screen and tube, and forced through the oil pump. The pressure relief valve bleeds off any excess oil pressure and re-routes it back to the oil pan. The pump directs the oil to the oil filter where it is cleaned. If the oil filter is too dirty the pressure in the filter will build until a bypass valve, built in the filter, opens and allows the oil to go to the engine without cleaning. From the filter, the oil makes its way through oil galleries in the cylinder block to the crankshaft main bearings. It then flows through the hollow crankshaft to lubricate the connecting rod bearings. Other oil galleries in the block bring the oil to the top of the engine where the camshaft bearings, lobes and the valve lifters are lubricated. On some engines, push rods on top of the lifters deliver oil to rocker arms and valve stems.
The oil returns to the oil pan via gravity. Drain passages in the head allow the oil that has collected to flow through. Some of the oil returning to the pan hits the rotating crankshaft and is splashed around lubricating the piston, piston rings and cylinder walls.
Oil pump and pressure regulator
The oil pump must provide a continuous supply of oil at sufficient pressure and quantity to provide adequate lubrication to the entire engine. It 
picks up oil from the reserve in the oil pan through the inlet screen and pickup tube. The oil is forced out of the pump outlet to a pressure regulator valve, incorporated in the pump. Bearing clearances and metered oil holes in the engine restrict the flow of oil from the pump resulting in a pressure build-up. To limit this pressure, oil is returned to the oil pan through the pressure regulator valve.
Two types of pumps
a) the rotor type
b) the gear type
One of the rotors, or gears is driven by a shaft from the crankshaft, camshaft, distributor shaft or timing belt. Because the oil can not flow through from the inlet to the outlet without being pressurized by the rotors or gears the pumps are classified as positive displacement pumps.
As the oil pump starts to wear the oil can bypass back to the inlet side causing the oil pressure to drop resulting in insufficient lubrication and parts failure.
Oil Filters
The function of the oil filter is to remove dirt, sludge and dust from the oil. Oil filters should be changed every time the engine oil is changed. 
Oil filters are designed to trap foreign particles suspended in the oil to prevent them from getting to engine bearings and other parts. Modern engines use the full flow filtering system. This means that all the oil goes through the filter before it goes to the engine parts.
The filter accomplishes the filtering task with the use of a filter element made from folded (pleated) paper. The folds provide a large filtering area within a small container. If the filter becomes clogged a special valve called the bypass valve will open and allow the oil to go to the engine parts without going through the filter. Another valve prevents the oil from draining out of the filter when the engine is stopped.
Filters come in different sizes and are rated in micron ratings. Micron rating refers to how small the dirt particles are that the filter will let through.
Oil Filter Identification
Oil filters are identified by a number printed on the outside metal shell and/or on the box the replacement filter comes in. The number can be cross-referenced in books or data base to find out which application it is intended for. Each of the oil filter manufacturers has their own numbering system.
How to find the correct oil filter for your vehicle or application.
- Look in the vehicle’s owner’s manual and/or service manual.
- Look on the old filter and find the number.
- Find the year, make, model and engine size of the vehicle and look it up in the reference book or data base or contact the dealer.
- Use the Vehicle Identification Number (VIN) on the registration or the vehicle and look it up in the reference book or data base or contact the dealer.
Oil Pressure Indicators
Oil pressure indicators inform the driver of the pressure or lack of pressure in the lubrication system. There are two types:
- oil warning light
- pressure gauges.
Pressure gauges use pressure sensitive, direct acting gauges or variable resistance sending unit switches.
Oil Route
- Starts in oil pan
- Drawn up through pickup screen and tube to pump
- Pressure relief valve bleeds off excess
- Pump directs oil to filter (bypass)
- Through oil galleries to main bearings
- Through crankshaft to connecting rod bearings
- Through oil galleries to top of engine (camshaft bearings, lobes, valve lifters)
- Returns to the oil pan via gravity
Key Terms and Definitions
- Bypass: When oil is diverted from its’ regular route.
- Full Flow: All the engine oil used in the engine must pass through the oil filter.
- Inlet: Where oil enters the pump.
- Lubrication: Reduce friction between two (2) parts by using oil, grease, etc.
- Micron rating: System for classifying oil filters.
- Oil cooler: Cools motor oil to reduce oxidation.
- Oil filter: Removes impurities in the oil.
- Oil galleries: Passages in the engine used to move oil to the various parts.
- Oil level indicator: Also referred to as a dip stick.
- Oil pan: Detachable lower part of the engine made of sheet metal. Encloses the crankcase and provides a reservoir for the oil.
- Oil pressure indicator: Gauge or light that indicates oil pressure.
- Oil pump: A mechanical device that forces oil, under pressure, to the moving engine parts.
- Oxidation: Air (oxygen) is mixed in with the engine oil due to excessive heat.
- Pressure regulator: A valve that limits engine oil pressure.
- Pick up tube: A pipe that extends from the oil pump into the oil.
- Sending unit: Changes oil pressure (mechanical) into a voltage (electrical).
- Sump: A reservoir for storing the engine’s oil. Also referred to as the oil pan.
Safety
Engine oil should be changed hot. If the engine is cold when the oil is changed, it gives particles of dirt and water time to stick to parts of the engine. When the oil is drained, the dirt and water stay in the engine. If the oil is still hot the particles remain suspended and are thus flushed out when the oil is drained.
- Always wear eye protection when changing oil. Hot oil could splash into your eyes and/or dirt get into your eyes while under the car.
- Be careful not to let any of the hot oil get on your hands as it may burn you.
- Oil is a carcinogenic and should not be left on your skin. Be sure to wipe off all the oil from your hands.
- When loosening the drain plug, pull the wrench toward you rather than pushing it away from you so that you are able to maintain your balance.
- Always apply some resistance when pulling to prevent the wrench from hitting you in the face.
- Be cautious of the exhaust system when under a vehicle. If the engine is still hot, the exhaust will also be and can burn you.
- If necessary, wear gloves to prevent any injury.
- Dispose of the used oil in the appropriate waste oil container.
-
Note: Observe all the safety rules related to the floor jack and hoist module. If you are unfamiliar with the rules related to this module, see your instructor for further information.
NEVER POUR THE USED OIL DOWN THE DRAIN.
This is an excellent well written article. Very informative.