Mazda Training manual - part 248

 
5 – LUBRICATION SYSTEM 

 

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OIL PUMPS

 

 
The oil pump pulls oil from the oil pan and pressurizes it so it will flow through the 
lubrication system. The oil pump is usually mounted on the cylinder block or the front 
engine cover. Most oil pumps are driven by the camshaft or crankshaft, using a gear and 
chain. 
 
Engine oil pumps are classified as positive displacement pumps. This means that all oil 
entering the pump also comes out. Oil is not allowed to circulate inside 
the pump. 

 

 

 
Pressure Relief Valve

 

 
Oil pumps include a pressure relief valve, which limits the oil pressure that the pump can 
develop. The faster an oil pump is driven, the more oil it pumps. So the capacity of the 
pump will always be more than the engine needs. 
 
If all the oil from the pump were forced into the oil passages, the oil would quickly heat up 
and break down. To limit the oil pressure, the pressure relief valve opens at a preset 
pressure and sends some of the oil from the pump’s outlet back into the inlet. In some 
engines, the oil from the pressure relief valve is diverted back into the oil pan. 
 
Excessive oil pressure damages seals and gaskets, causing oil leaks. Two main types of oil 
pumps are typically used: rotor-type pumps and gear-type pumps. 

 
5 – LUBRICATION SYSTEM 

 

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FIGURE 53. A 
rotor-type, or 
trochoid, oil 
pump uses 
rotors with 
rounded lobes to 
push oil through 
the pump. 
 

Inner rotor 

Outer rotor 

Outlet port 

Pressure 
relief valve 

Inlet port 

Engine oil 

Pump body

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Rotor-Type Pump (Trochoid)

 

 

A rotor-type, or trochoid, pump uses two rotors, one turning inside the other, 
to pressurize the oil. The two rotors turn at slightly different speeds. The 
rotors have smooth, rounded lobes. These types of rotors are called 
trochoid gears. Figure 53 shows a typical rotor-type oil pump. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
In this design, the inner rotor is driven by the crankshaft. The inner rotor 
turns the outer rotor. As the two rotors turn, pumping cavities are formed 
between the lobes on the two rotors. Oil is drawn into these cavities at the 
inlet port of the pump. The pumping cavities become smaller and larger as 
the lobes on the two rotors mesh. This squeezing action pushes the oil 
through the pump to the outlet port. 

 

 
5 – LUBRICATION SYSTEM 

 

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The simple design of the rotor-type pump makes it very reliable. In addition, 
rotor-type pumps can withstand high-speed operation, and they produce a 
smooth flow of oil, rather than a pulsing action. 

 

The rotor-type pump used on Mazda engines has a small hole at the outlet 
side to allow air to escape. If there is no oil in the pump because the 
vehicle has not been driven for a long time, the air hole vents the air 
quickly when the engine is started. This allows oil to flow almost 
immediately to critical engine parts. 
 
 
Gear Pump

 

 

In a gear-type oil pump, two gears are used to push the oil through the 
pump. Figure 54 shows how a typical gear-type pump operates. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The drive gear is driven by the camshaft or crankshaft. As the drive gear 
turns, it meshes with the driven gear, which turns in the opposite direction. 
As the gears turn within the pump body, they create a vacuum  — an 
area that has no gas or fluid in it — at the inlet port. Oil is drawn into this 
vacuum. The oil moves between the gears and the pump body to the 
outlet port. 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

FIGURE 54. A 
gear-type oil 
pump uses a 
drive gear and a 
driven gear 
turning in 
opposite 
directions.

 

 

Outlet port

 

Drive gear 

Driven gear 

Inlet port

 

 

 
5 – LUBRICATION SYSTEM 

 

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FIGURE 55. The 
paper element in 
the oil filter traps 
particles and dirt 
in the oil.

 

 

Paper 
element

 

Flow to 
main gallery

 

Flow from 
oil pump

 

Spring 

Bypass 
valve

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

OIL FILTER

 

 
The engine oil filter traps very small particles that may get through the oil 
strainer. Mazda oil filters are the full-flow type. This means that all the oil 
pumped by the oil pump passes through the oil filter. The filter contains a 
paper element that screens out particles in the oil. 
 
A typical oil filter is shown in Figure 55. Oil flows from the oil pump and 
enters the oil filter through several holes. The oil first flows around the 
outer part of the filter element. Then it passes through the filter material 
into the center of the element. Finally, the oil flows out to the main gallery 
through a tube in the center of the filter. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The filter screws onto the main oil gallery tube. A seal prevents oil from 
leaking at the connection between the filter and the cylinder block. 
 
 

 

Bypass Valve

 

 

As the element in the oil filter becomes dirty, the oil pump must work 
harder to push oil through the filter. If the filter becomes fully clogged, the 
engine could be starved of oil, and important parts such as the crankshaft 
bearings could be damaged.