5 – LUBRICATION SYSTEM
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Piston Engine Fundamentals
TC010-05-01S
To prevent this type of damage, the filter also includes a spring-loaded bypass valve. This
valve “senses” the back-pressure from the filter as it becomes clogged. When the
back-pressure becomes great enough to overcome the spring on the bypass valve, the
valve opens, allowing some of the oil to bypass the filter and go directly to the oil gallery
tube.
Anti-Drainback Diaphragm
Mazda oil filters also contain an anti-drainback diaphragm, which keeps oil in the filter when
the engine is shut off. The diaphragm covers all the filter inlet holes when the oil pump
stops. When the engine is shut off, the pressure of the oil in the filter forces the diaphragm
down on the holes, sealing oil in the filter.
When the engine starts again, oil flows immediately from the filter. In this way, critical
engine parts receive lubrication right away. As the pressure from the oil pump grows, the
diaphragm is pushed away from the holes, allowing normal oil flow to begin again.
SEALING MATERIALS
At various locations in the engine, seals and gaskets keep the oil from leaking. The most
common material used for sealing the lubrication system is synthetic rubber. In critical
areas, it may be bonded to metal or fiber. Natural rubber is never used because engine oil
will break it down.
When seals or gaskets are replaced, the surfaces must be cleaned completely before
the new seal or gasket is installed. In addition, the bolts that secure the seal must be
tightened to the correct tightness, or torque, in the proper order.
When a properly installed seal or gasket begins to leak, the cause is usually excessive
internal pressure, worn bearings, a bent shaft, or a rough sealing surface.