1. Chapter 39
Cooling System
Fundamentals

2. Functions Cooling System 1. Remove Engine Heat
Combustion can reach 4500 ºF (2500 ºC)
This is hot enough to melt metal parts
Cooling system removes excess heat

3. 2. Maintain Operating Temperature
180 ºF to 210 ºF (80 ºC to 100 ºC)
When an engine warms to operating temperature, parts expand
Ensures that clearances are correct
Ensures proper combustion, minimum emissions, and maximum performance

4. 3. Reach Operating Temperature Quickly
This minimizes several conditions:
poor combustion (poor fuel vaporization)
part wear
oil contamination
reduced fuel economy
increased emissions

5. 4. Heater Operation
Cooling system circulates coolant to the vehicle’s heater
Engine heat is used to warm the passenger compartment

6. Cooling System

7. Cooling System Operation
Water pump forces coolant through engine water jackets
Pump is belt or gear driven off the crankshaft

8. Cold Engine Operation Thermostat is closed
Coolant circulates inside the engine
Engine warms quickly

9. Hot Engine Operation At operating temperature, thermostat opens
Heated coolant then flows through the radiator
Excess heat is transferred from the coolant to the air flowing through the radiator

10. Cooling System Types Two common types: 1. air cooling
2. liquid cooling

11. 1. Air Cooling Systems
Large cylinder cooling fins and outside air remove excess heat
Cooling fins increase the surface area of the metal around the cylinder
This allows enough heat transfer to the outside air
Plastic or metal shrouds duct air over the cylinder fins

12. 2. Liquid Cooling Systems
Circulate coolant through the water jackets
Combustion heat is transferred to the coolant
Cooling system carries it out of the engine

13. Liquid Cooling Advantages
Precise temperature control
Less temperature variation
Reduced emissions
Improved heater operation

14. Air Cooling Versus Liquid Cooling

15. Heat is transferred to cylinder wall, into coolant and carried away
Liquid Cooling
Heat is transferred to cylinder wall, into coolant and carried away

16. Conventional Coolant Flow
Hot coolant flows from the cylinder head to the radiator
After being cooled in the radiator, the coolant flows back into the engine block

17. Reverse Flow Cooling
Cool coolant enters the head and hot coolant exits the block to return to the radiator
Helps keep a more uniform temperature throughout the engine
Found on high-performance engines

18. Basic Cooling System Components: water pump radiator hoses radiator
fan
thermostat

19. A ribbed belt powers this pump
Water Pump
A ribbed belt powers this pump
Crank pulley
Water pump pulley
Impeller
Ribbed belt

20. Impeller Pump
Coolant is thrown outward by centrifugal force, producing suction in the center of the pump housing

21. Coolant Flow

22. Coolant Flow (Conventional)
Coolant flows out of the radiator, through the lower hose, into the engine
It then flows through the pump, around the cylinders, through the heads, up through the thermostat, and back into the radiator

23. Hoses Radiator hoses Heater hoses
carry coolant between the engine water jackets and the radiator
lower hose is exposed to water pump suction so a spring may prevent collapse
Heater hoses
carry hot coolant to the heater core
smaller diameter than radiator hoses

24. Radiator and Heater Hoses

25. Two basic types of radiator hoses

26. Three basic types of hose clamps

27. Transfers coolant heat to the outside air
Radiator
Transfers coolant heat to the outside air

28. Radiator Types
Downflow
Crossflow

29. Radiator Cap Seals the radiator Pressurizes the system
Relieves excess pressure
Allows coolant flow between the radiator and the coolant reservoir

30. Radiator Cap

31. Radiator Cap Pressure Valve
Spring-loaded disk
Normally, water boils at 212 ºF (100 ºC)
For each pound of pressure increase, boiling point goes up about 3 ºF (1.6 ºC)
Typical pressure:
12–16 psi
raises boiling point to 250–260 ºF (121–127 ºC)

32. Radiator Cap Vacuum Valve
Opens to allow flow back into the radiator when the coolant temperature drops

33. Closed and Open Cooling Systems Closed cooling system
uses an expansion tank
overflow tube is routed into reservoir tank
Open cooling system
allows excess coolant to leak onto the ground

34. Pressure Cap Operation
Hot engine

35. Pressure Cap Operation
Cold engine

36. Cooling System Fans Pull air through the core of the radiator
Increase volume of air through the radiator
Driven by fan belt or electric motor

37. Ensures that the fan pulls air through the radiator core
Radiator Shroud
Ensures that the fan pulls air through the radiator core

38. Thermostat
Senses coolant temperature and controls coolant flow through the radiator
Reduces coolant flow on cold engine
Increases coolant flow on hot engine

39. A temperature-sensitive valve
Thermostat
A temperature-sensitive valve

40. Thermostat Operation Cold engine Hot engine
wax-filled pellet has contracted
spring holds valve closed
Hot engine
when heated, pellet expands
spring tension is overcome
valve opens

41. Thermostat Operation
A. Cold engine
B. Hot engine

42. Thermostat Operation
Cold engine

43. Thermostat Operation
Hot engine

44. Permits circulation through the engine when the thermostat is closed
Bypass Valve
Permits circulation through the engine when the thermostat is closed

45. Antifreeze Composed of ethylene glycol mixed with water
Prevents winter freeze-up
Prevents rust and corrosion
Lubricates the water pump
Cools the engine

46. Protected with antifreeze
Corrosion Protection
Protected with antifreeze
Water only

47. Antifreeze/Water Mixture
Lowers coolant freezing point to about -34 ºF (-37 ºC)