Mazda Training manual — part 249

5 – LUBRICATION SYSTEM

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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.

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REVIEW EXERCISE 7

Fill in the words that correctly complete these sentences. Check your answers with the
answer key on page 85.

1. The component in the bottom of the oil pan that filters out large particles is called the

______________________.

2. The largest oil passage in the cylinder block is called the

__________________________.

3. As oil is pushed off lubricated surfaces by new oil, it collects at the bottom of the engine

in the ______________________ .

4. An oil pump that uses two rotors, one turning inside the other, is called a

_____________________ -type pump.

5. The ________________________ contains a bypass valve and an anti-drainback

diaphragm.

6. Which of these symptoms would you expect in an engine that has a damaged oil

pump? More than one answer may be correct.

A. high idle

B. noisy engine

C. dirty oil filter

D. low oil pressure

6 – COOLING SYSTEM

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Most engines are cooled by a steady flow of liquid coolant through the cylinder block and
heads. The cooling system is one of the automobile’s most important systems. It removes
excess heat produced during combustion and keeps the engine operating at its most
efficient temperature. If the cooling system fails, the engine can overheat and seize. An
operating temperature that is too cool results in poor gas mileage and incomplete
combustion. The hot coolant is also used to operate the heater for the passenger
compartment. This section describes how the cooling system works.



OBJECTIVES

After completing this section, you will be able to:


• Identify important parts of the cooling system and describe how they work.

•

Identify the important parts of a water pump and describe how they operate.

•

Describe the differences between downflow and crossflow radiators.

•

Describe how the radiator reservoir works.

•

Identify the important parts of the pressure cap and describe how they work.

•

Describe how the thermostat works.

•

Describe the differences between mechanical and electric fan drives.

•

Describe how a viscous drive clutch works.

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FIGURE 56. The
cooling system
circulates coolant
throughout the
engine.

Water pump

Coolant
passages

Thermostat

Radiator
reservoir

Fan

Pressure cap

Radiator

COMPONENTS

The cooling system maintains an efficient operating temperature. About
one third of the heat created by combustion is removed by the cooling
system. Important parts of the cooling system are shown in Figure 56.
These parts are described in the following paragraphs.


Coolant

In early engines, water alone was used as coolant. Today, most engines
use an ethylene-glycol-based coolant mixed with water that lowers the
freezing point of water, raises the boiling point of water, adds water pump
lubrication, and prevents engine corrosion.


Because coolant is toxic, never dump it down a drain.