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.

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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.

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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

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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.