A Guide To How Different Car Oil Pumps Work

Did you know your vehicle needs oil to run smoothly? Not sure how the oil pump works? In any vehicle, there are many highly stressed and constantly moving components which require continuous lubrication to help reduce the risk of excessive wear along with stopping the components from seizing up. The overall function of an oil pump is to supply adequate amounts of oil to those parts when they’re under-pressure. The reliability of the engine largely comes down to how efficient lubrication is and how well the oil pump is working. The job of the oil pump is to force the oil needed out of the sump and into the system at a high enough pressure to reach all the contact points and bearings. Because of this important task, the oil pump must be long lasting and reliable. The vehicle type will depend on what type of oil pump is used. The following is a guide to how the different oil pumps work.

Different Oil Pumps And Their Operation

Gear Type Oil Pump

The gear type oil pump is one of the most common types used in vehicles. This type consists of two meshing gears that are designed to easily rotate within a close-fit housing. When the gears rotate they help to carry the oil around and against the housing. The meshing gear teeth forces the oil out of the oil pump. The gear type oil pump produces a positive oil flow to numerous engine components to help keep everything lubricated. Alternatively though, if the engine oil used is thick, it can cause a pressure build-up due to the force needed to push the oil through the small bearing clearances. This in turn could damage the pump. To help eliminate this from occurring, an oil pressure relief valve is installed. This helps to return the oil to the sump when the pressure which is created exceeds the maximum value.

The Rotor Oil Pump

Another common type of oil pump is the rotor oil pump. This pump features a rotor with up to four or five external lobes. These lobes rotate within the outer ring which has five to six internal lobes. The inner rotor axis is offset by the outer ring axis. The effect of this setup is to have a balanced volume between the lobes as the two rotated. This results in the oil to be pulled between the lobes and forced out into the discharge tube of the pump. This action is similar to that of the rotary engine. The rotor oil pump also features a pressure relief valve in its design.

Eccentric Rotor Oil Pump

In modern cars today, the eccentric rotor oil pump is the most commonly used oil pump. An external and internal rotor which are installed eccentrically to one another make up the main components of this oil pump. There’s a number of lobes within each rotor. For example, the inner rotor features up to four lobes which are mounted on the exterior face. The outer rotor features up to five lobes which face inwards. The configuration of each pump differs, however the number of lobes which are on the outer rotor is always more than the number that the inner rotor has. These rotors are installed within the body of the pump and feature crescent-shaped outlet and inlet ports. The inner rotor rotates when the camshaft is moved thus resulting in the rotation of the outer rotor. During this process, the vehicle oil is drawn inwards through the inlet port before being trapped between each opposing lobe.

The clearance between lobes decrease when the rotor revolves faster. This can cause a pressure build up until the outlet port is exposed. When the rotor’s edge passes the outlet port under pressure, the oil is forced into the lubrication system. The process is repeated until a continuous flow of oil is created. The rotor pump is the most efficient of all pumps and is fitted these days by many manufacturers.

Double Gearwheel Oil Pump

Although not as commonly used in modern day cars today, the double gearwheel oil pump is still used in some Audi vehicles. This type of pump works similar to an eccentric rotor pump, however the difference is that the oil is pumped by the spaces which are formed between each of the gear teeth and not the lobed rotors. Both gearwheels are meshed together with one being driven by the camshaft while the other rotates in turn. These are housed with only a small clearance in the body of the pump. On opposite sides of the pump, inlet and delivery ports are provided. The rotation of the gearwheels form an inlet port depression and draw oil into the pump. Oil is then carried between the adjacent gear teeth and around the pump. The meshing movement of the gearwheels on the opposite side of the pump forces oil into the delivery port from the tooth spaces and into the lubrication system. Depending on the design of the double gearwheel pump, some gearwheel pumps have one less tooth than others. This helps to create even wear of the gearwheel over time. This type of oil pump is reliable and simple but does have a tendency to leak when exposed to higher pressures. This can be overcome however by mounting the oil pump lower within the crankcase where it’s immersed within the oil. This can be 25 percent less efficient than the rotor pump.


The above oil pumps are just some that are used in vehicles right around the world. The oil pump is one of the crucial parts of the entire function of a vehicle’s whole operation. Without it, the components within the vehicle would seize up, resulting in an inability for the vehicle to move as it normally would. Oil pumps should be serviced each year to ensure proper function and operation. This should be carried out by a trained professional. So how is your vehicle running? Do you think the oil pump needs a service?

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