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The Engine Oil System

The oil system in the vehicle engine is designed to aid in friction reduction, lubricate, and cool moving parts. The oil system is one of, if not the most important system, that you should be knowledgeable of. When working and maintained properly this system can ensure long life of your engine.

Main Types of Oil Systems

  • Dry sump
  • Wet sump

Dry Sump

This describes a system that continually moves oil by way of internal and external oil pumps. The oil does not sit in the oil pan and wait to be picked up by the oil pump. It is suctioned or pumped out of the sump or pan by an oil pump and sent to an air/oil separator. From here it is moved by another pump and sent back into the top of engine to lubricate and cool the internal engine components. This is not a common system for everyday passenger vehicles. This system is mainly used in race engines and other types of high performance vehicles because of cost and capabilities.

Wet Sump

This describes a system that picks up the oil from the pan or sump and pumps it to the top of the engine while keeping the oil inside the engine. Oil is suctioned from the bottom of the pan through the pickup screen and tube by the oil pump. It is then pumped to the top of the engine through galleys to the internal engine components. Eventually it falls back into the pan via drain holes and gravity. This system is on most all passenger vehicles due to cost, practicality, and reliability.

Components of the Oil System

This is a list of the minimum required parts.

  • Pan
  • Drain plug
  • Suction screen and tube
  • Pump
  • Galleries
  • Filter
  • Filler cap
  • Dipstick
  • Dipstick tube
  • Pressure sending unit
  • Pressure gauge

Optional Components

  • Cooler
  • Level sensor


The pan or sump is mounted to the bottom of the engine. It holds the oil that the engine needs to stay lubricated and cool. Some designs today are made in two pieces. The upper piece is generally considered to be part of the engine block or crankcase. The lower portion is typical of any standard stamped steel or cast aluminum oil pan.

Drain plug

The drain plug allows the engine oil to be drained when it is removed. It is located on the lowest portion on the pan. Drain plugs may require a crash gasket to seal against the oil pan. Note- Some manufacturers and models like Mercedes do not have a drain plug. The oil is suctioned out of the pan through the dipstick tube.

Suction screen and tube

The suction tube and screen are mounted to the oil pump. The suction tube and screen act like a straw to pick up the oil in the pan when the oil pump turns.

Oil pump

The pump is what allows the engine oil to move throughout the engine. It may be driven by either the camshaft or crankshaft. The pump may contain a pressure valve and/or restriction that pressurizes the oil. This pressure created by the pump ensures that the engine oil can flow throughout the entire system adequately.


The galleries are the passageways cast into the engine block that allow the engine oil to flow to various parts of the engine.


The filter removes particles that are generated by normal operation. The oil filter is a critical maintenance item on any internal combustion engine. Always change it and the oil at the specified intervals stated by your vehicle manufacturer.

Filler cap

The filler cap is what is removed when oil needs to be added to the engine. The filler cap is located on top of the engine on a valve cover.


The dipstick allows the operator to check the oil level in the engine. Always check both side of the dipstick and trust the low side of either side.

Dipstick tube

The dipstick tube houses the dipstick. It may be mounted into the oil pan or engine crankcase.

Pressure sending unit

The pressure sending unit is a switch that measures the amount of pressure in the system. It is mounted on the engine and intersects an oil galley. It sends oil pressure information to a gauge and/or light on the instrument cluster.

Pressure gauge

The pressure gauge is a display on the instrument cluster that informs the operator of the amount of pressure in the engine. Normal pressure ranges vary. Consult your manufacturer or trusted technician for proper specifications.

Optional Components

The following components may be offered by the manufacturer or as an aftermarket install.


Coolers are optional on some vehicles. They allow the engine oil to flow outside the engine and cool down. Cooling may occur by air flow, heat exchange with the cooling system, or a combination of both.

Level sensor

The level sensor indicates the amount of oil in the crankcase. This is accomplished by some form of notification to the operator on the instrument cluster.

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