Mazda Training manual - part 249

 

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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. 

 
5 – LUBRICATION SYSTEM 

 

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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.

 

 

 
6 – COOLING SYSTEM 

 

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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.

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

 

 

 

 

 

 

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