Mazda Training manual - part 251

 

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Mazda Training manual - part 251

 

 

 
6 – COOLING SYSTEM 

 

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Piston Engine Fundamentals

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REVIEW EXERCISE 8

 

 
Fill in the words that correctly complete these sentences. Check your answers with the 
answer key on page 91.

 

 
1.      Coolant lowers the freezing point of water and ______________________ the boiling 

point. 

 
2.   The _____________________ helps the engine warm up by restricting coolant flow 

until a certain temperature is reached. 

 
Use the water pump illustration below to complete the following two items.

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
3.      Item        in this illustration is the _______________________. 
 
4.      Item        in this illustration is the _______________________. 
 
5.      Which of these symptoms would you expect to find in an engine that has a failing 

water pump? More than one answer may be correct. 

 

A. overheating 
 
B. noisy tappets 
 
C. hard starting 
 
D. gasoline fumes 

 

 
6 – COOLING SYSTEM 

 

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FIGURE 60. A 
downflow-type

 

radiator has an 
upper and lower 
tank.

 

 

Coolant inlet

 

 

Upper tank

 

 

Lower tank

 

 

Coolant 
outlet

 

 
Core

 

RADIATORS

 

 
Mazda uses both downflow and crossflow radiators. 
 
Downflow-Type

 

 
Figure 60 shows a typical downflow-type radiator. As its name suggests, 
the downflow radiator has an upper and lower tank. Tubes connect the 
tanks. Coolant flows down from the upper tank through the core and into 
the lower tank. Cooling takes place as the liquid passes through the 
radiator core. If the vehicle has an automatic transmission, the radiator 
may have a separate cooler at the bottom for the automatic transmission 
fluid. 

 
 
 
 
 

 
 
 

 
 

 
 
 
 
 
 
 
 

Coolant Flow

 
6 – COOLING SYSTEM 

 

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Crossflow-Type

 

 
The crossflow-type radiator is also commonly used. In this design 
(shown in Figure 61), the tanks are on the side of the core, so the 
coolant flows through tubes from one side to the other.

 

 
 

 
 
 

 
 

 
 
 

 
 

 
 
 
 

 
 

 
 
 
 
 

 
 
 
 

 
 

FIGURE 61. A 
crossflow-type 
radiator has side 
tanks. 
 

 

Right tank

 

 
Left tank

 

 
Coolant inlet

 

 
Coolant outlet

 

 
Core

 

 
 
 
 
 
 
 
 

Answers to 
Review Exercise 
8

 

 
1. lowers 
 
2. thermostat 
 
3. water seal 
 
4. impeller 
 
5. A — over- 

heating

 

 

Coolant Flow

 
6 – COOLING SYSTEM 

 

92

Piston Engine Fundamentals

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FIGURE 62. As 
the coolant 
expands, the 
excess coolant 
flows into the 
reservoir. As it 
contracts, it is 
drawn back into 
the radiator.

 

 

 

Radiator 
reservoir hose

 

 

Overflow tube

 

Radiator Reservoir

 

 

Coolant level is checked and coolant is added at the radiator reservoir. A 
hose connects the reservoir to the radiator filler neck, as shown in Figure 
62. As engine temperature rises, the expanding coolant flows from the 
radiator into the reservoir. When the engine is stopped, the coolant 
temperature drops and contracts. A partial vacuum develops in the 
cooling system, drawing coolant from the reservoir backinto the cooling 
system.

 

 
 

As shown in Figure 62, the reservoir has an overflow tube that allows 
coolant to escape if the cooling system is overfilled or when the engine 
overheats.

 

 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 

PRESSURE CAP

 

 

The pressure cap on the radiator maintains pressure in the cooling 
system. The boiling point of a liquid rises with the amount of pressure it is 
under. For example, water at sea level boils at about 212 degrees 
Fahrenheit. Water in a typical pressurized cooling system boils at more 
than 250 degrees Fahrenheit. So pressurizing the cooling system 
effectively raises the operating temperature of the engine. 
 
Figure 63 shows a typical radiator pressure cap, which fits on the filler 
neck on the radiator. The cap includes a pressure valve (or blow-off 
valve) and a vacuum valve. Both are spring-loaded to remain closed 
when the system is within operating ranges. 
 

To filler neck

 

 

 

 

 

 

 

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