Mazda Training manual - part 250

 
6 – COOLING SYSTEM 

 

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Piston Engine Fundamentals

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Water Pump 

 

The water pump circulates coolant throughout the cooling system.

 

 
Coolant Passages

 

 
Coolant passages are cast into the cylinder block and cylinder head. 
These passages carry coolant around the cylinders and combustion 
chambers. The coolant picks up heat and carries it away from these 
parts.

 

 
Thermostat

 

The thermostat regulates engine temperature by controlling the flow of 
coolant until a certain preset temperature is met. This helps the engine 
warm up quickly and maintain a more even temperature.

 

 

Radiator Reservoir

 

 

As coolant becomes hot, it expands. The coolant recovery system 
stores the excess coolant released from the radiator. When the engine 
cools, the coolant in the reservoir is drawn back into the cooling system. 
This keeps the cooling system constantly full, increasing cooling system 
efficiency.

 

 

Fan

 

 

The radiator fan pulls cool outside air over the radiator surface to pick 
up heat from the coolant for faster heat transfer, especially during idling. 
Models equipped with air conditioning usually have an additional fan for 
increased cooling.

 

 
 

Pressure Cap

 

 

The pressure cap maintains pressure in the system which raises the 
boiling temperature of the coolant, preventing the coolant from 
evaporating or boiling off. This cap also allows excess pressure to 
escape from the system.

 

 

Radiator 

 

The radiator transfers heat from the coolant to the outside air. The 
radiator core contains tubes and fins. Coolant flows through the tubes, 
and the fins increase the radiator’s surface area exposed to the air. This 
allows the air to carry away more heat, reducing the coolant 
temperature.

 

 

Answers to Review 
Exercise 7

 

 
1. oil strainer

 

2. main gallery

 

3. oil pan

 

4. rotor or trochoid

 

5. oil filter

 

6. B & D

 

 

 
6 – COOLING SYSTEM 

 

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Piston Engine Fundamentals

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FIGURE 57. Coolant 
flows from the 
cylinder head 
passage through 
the radiator and 
water pump to the 
cylinder block.

 

HOW COOLANT CIRCULATES

 

 
Figure 57 shows how coolant circulates through the cooling system. The 
numbers in this figure match the numbered steps in the description that 
follows. 

 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 

To/from heater

 

 
6 – COOLING SYSTEM 

 

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When a cold engine is started, the water pump only circulates coolant through the 
cylinder head and engine block coolant passages, quickly raising the engine 
temperature.

 

 

When enough heat is created to open the thermostat, the water pump circulates 
coolant throughout the engine and into the radiator.

 

 

The hot coolant flows from the upper tank of the radiator, to the lower radiator tank. 
Cool air passing over the radiator fins removes heat from the coolant. 

 

From the lower tank, coolant flows through the lower radiator hose to the water pump 
inlet.

 

 

The water pump circulates the coolant through the pump outlet into the cylinder block 
coolant passage.

 

 

Coolant flows from the cylinder block passage into the cylinder head coolant passage 
to complete the circuit.

 

 
   

As Figure 57 also shows, some of the coolant may be diverted to the heating system, which 
heats the passenger compartment of the vehicle. 
 
 
WATER PUMPS

 

 
Most water pumps are impeller or non-positive displacement pumps. This means that all the 
water that enters the pump does not necessarily have to come out of the pump. This design 
is different from the oil pump (a positive displacement type), in which all the oil that enters 
the pump is pumped out. 
 
 
Impeller-Type Pump

 

 
Water pumps are usually designed as simple impeller-type pumps. Figure 58 shows the 
parts of a typical impeller-type water pump. 

 
 

 
6 – COOLING SYSTEM 

 

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Piston Engine Fundamentals

TC010-05-01S

FIGURE 58. 
Water pumps are 
simple impeller- 
type pumps

. 

 
 

Pump pulley 
 
Shaft and 
bearing 
assembly

 

 
Pump body

 

 
Water seal

 

 
Impeller

 

 
Pump inlet

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
FIGURE 59. 
Centrifugal force 
pushes coolant 
from the center of 
the impeller to the 
outside edges of the 
impeller.

 

 

Pump inlet

 

Impeller

 

Pump outlet

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

The water pump has a pump body, which holds the impeller (also called 
a vane or rotor). The impeller turns on a shaft that is connected to a 
pulley driven by the crankshaft. The impeller shaft is supported by a 
bearing. A water seal keeps coolant from leaking out of the pump. A worn 
bearing or impeller shaft causes the seal to leak.

 

 
 

Centrifugal Operation

 

 

The impeller-type pump operates on centrifugal action, which is the 
tendency of a rotating weight to be pushed outward. Coolant flows 
through the pump inlet and enters the center of the impeller, as shown in 
Figure 59. As the impeller rotates, it “slings” the coolant to the outside 
edges of the impeller. The coolant is trapped by the pump body and 
forced into the pump outlet.