Always Learning. CHAPTER 17 Cooling System Theory

Always Learning

CHAPTER 17

Cooling System Theory

Automotive Heating and Air Conditioning, 6/eBy Thomas S. Birch

Copyright © 2012, 2010, 2006, 2001, 1997, 1991 Pearson EducationUpper Saddle River, NJ 07458 • All rights reserved.3

After studying Chapter 17, the reader will be able to:

1. Understand the cooling system’s role in maintaining proper engine temperature.

2. Realize the effects that overcooling and overheating have on an engine.

3. Understand what the parts of the cooling system do and how they operate.

4. Understand what coolant is and what can happen if it is not properly maintained.

OBJECTIVES



KEY TERMS• Coolant • Coolant pump • Coolant recovery reservoir (CRR) • Core • Core hole plug • Corrosion protection • Crossflow • Downflow • Drive belt • Ethylene glycol (EG) • Extended-life antifreeze • Fan belt • Fan clutch • Fin-and-tube design • Freeze plug • Inorganic additive technology (IAT) • Hoses• Hybrid organic a cid technology (HOAT)• Jiggle pin

• Organic acid (OA) • Organic acid technology (OAT) • Passivate • Pressure cap • Propylene glycol (PG) • Relay • Reverse coolant flow • Serpentine V-ribbed belt • Shroud • Soft plug • Stretch-fit • Thermostat • Thermosyphon • V belt • Water jacket • Water pump



INTRODUCTION

• Automotive engines use a cooling system to remove excess combustion heat. • Modern cooling systems are designed to maintain

an even temperature of about 180 to 230°F (82 to 113°C); this is at or above the boiling point of water.

• A coolant mixture of water and antifreeze is used, and, because it is under pressure, the coolant has a still-higher boiling point.

• The cooling system consists of the engine’s water jackets, thermostat, water pump, radiator, fan, radiator hoses, and coolant.



WATER JACKETS

• When an engine cylinder block and head are cast, cavities called water jackets are formed around the cylinder walls and combustion chambers. • These water jackets allow coolant to circulate

around the very hot areas, including the exhaust valve seats, as well as the relatively cooler areas of the lower cylinders.

• The coolant absorbs heat from the hot areas and transfers this heat to the colder areas in the engine or radiator.



THERMOSTAT

• The thermostat is a temperature-controlled coolant valve. • In most engines, it is located at the upper radiator

hose connector, which forms the thermostat housing. • In a few engines the thermostat is located at the

lower radiator hose or inlet connection.• The two major functions of a thermostat are to

speed up engine warm-up and to regulate operating temperature.



WATER PUMP

• In most vehicles, the water pump is driven by the accessory drive belt, commonly called the drive belt or fan belt , at the front of the engine.

• Coolant enters at the center of the pump, is caught by the impeller, and is spun outward to the outlet.

• Weep Hole placed between seal and the bearing.• Indicates leakage, wear and needs replacement

• DRIVE BELT• BELT TENSIONER



Does a Serpentine Belt Drive from Both Sides?

• Yes, a serpentine V-ribbed belt drives through the friction of the belt on the pulley so the belt must wrap farther around the pulley. A serpentine belt bends in both directions so that the back of the belt is used on some pulleys. The tensioner pulley or an idler pulley is positioned so that it will increase the amount of wrap around certain pulleys. The amount of wrap and the belt width allow the belt to handle the horsepower requirement.



What Is a “Stretchy” Belt?

• Starting in 2007, some vehicles use a stretchy/stretch-fit , multirib belt without a tensioner. The elastic nature of the belt allows it to be stretched to install it over the pulleys, and the stretch provides the tension to keep it from slipping. A special tool or strap is required to install stretchy belts, and some manufacturers say to cut the belt to remove it. Stretch-fit belts are used for low-power accessories.



• Belt Tension Install-Gates• http://www.youtube.com/watch?v=DbHumrLIdys

• Belt Tension-NAPA• http://www.youtube.com/watch?v=uGJCtWKkaTE&f

eature=related



RADIATOR

• The radiator is a heat exchanger that gets rid of excess engine heat. • Most radiators are of fin-and-tube design . • Coolant flows through tubes from the inlet tank to

the outlet tank. • The fins are attached to the tubes to provide the air

contact area.• The fin-and-tube area is commonly called the core.



RADIATOR

• PRESSURE CAP• COOLANT RECOVERY RESERVOIR• COOLING MODULES



FAN

• The fan ensures adequate airflow through the radiator while the vehicle is stopped or moving at low speeds. • At cruising speeds, the fan is not needed because

ram air through the grill supplies ample air. • This airflow is improved by an air dam under the

front bumper of some vehicles.• Fan takes between 2-6 horsepower



FAN

• FAN CLUTCH• ELECTRIC FANS

• ELECTRONICALLY CONTROLLED FAN CLUTCH.



TECH TIP

• Some vehicles use a combination of a mechanical fan with fan clutch and an electric fan.



HOSES

• Two large hoses connect the engine’s water jackets to the radiator.

• The upper hose transfers hot coolant to the radiator; the lower hose returns the coolant, which is now cooler, to the engine.• These hoses must be flexible to allow the engine to

move on the motor mounts. • Hose flexibility also removes the need for close

alignment of the connections between the radiator and engine.

• Hose flexibility also removes engine vibrations, which can shake a radiator apart.



HYBRID VEHICLE COOLING SYSTEM

• The engine cooling system of most hybrid vehicles is the same as that of other vehicles. • Others have features to help maintain heat in the

engine. • A vehicle with idle-stop operating in a city tends to

have very low coolant temperature.



HYBRID VEHICLE COOLING SYSTEM

• These features include:• Glow plugs: electric heaters mounted in the water

jackets to heat the coolant.• Hot coolant storage (thermos-like container):

connected to water jackets by hoses and an electric motor to circulate hot coolant through the water jackets while the vehicle is parked with the engine off.



GAUGES

• The gauge indicates the engine’s coolant temperature.• Remember that the normal cooling system

operating range is about 180 to 245°F (84 to 120°C).

• The lower end is the thermostat opening temperature, and the upper end is just below the coolant boiling point with the specified pressure cap and antifreeze mixture.



How Does a Mechanical Temperature Gauge Work?

• Most older vehicles used mechanical gauges that use a sending unit connected to the gauge by a thin capillary tube. The sending unit contains a gas that expands as it is heated. This gas pressure acts on a Bourdon tube to give a gauge reading.



COOLANT

• Coolant is the working fluid that transfers heat in a cooling system, much like the refrigerant in an A/C system. • Water is the base coolant because it is plentiful,

inexpensive, flows easily, and has an excellent ability to absorb and release heat.



ENGINE BLOCK HEATER

• Engine block heaters are small, electrical-resistance heater units that can be mounted in the cylinder block. • These heaters are plugged into ordinary 110-volt

AC house current and are used in very cold areas to warm an engine while it is shut off.

• Block heaters provide easier engine starting and faster warmup.



SUMMARY

1. Cooling systems maintain the proper coolant temperature for efficient engine operation.

2. The coolant flows through the engine’s water jackets to remove excess heat.

3. Coolant temperature is controlled by a thermostat.4. The water pump is driven by the accessory drive belt to push the

coolant through the system.5. The radiator is the heat exchanger to transfer coolant heat to air.6. Modern radiators use a pressure cap to increase coolant pressure and

boiling point.7. A coolant reservoir is used to collect expanding coolant so it can be

returned when the engine cools.8. Mechanical and electric fans ensure that enough air flows through the

radiator at low vehicle speeds.9. Coolant helps protect the engine from boiling, freezing, and corrosion.



REVIEW QUESTIONS

1. The vehicle’s cooling system is designed to keep the engine at the ______________ ______________ ______________ .

2. The plugs used to seal the large holes in the sides of the engine block are properly called ______________ ______________ ______________ .

3. The ______________ opens at a temperature of about 200°F to allow coolant to circulate between the engine and ______________ .

4. While the thermostat is closed, ______________ will circulate between the engine and the ______________ ______________ .

5. Many thermostats use a(n) ______________ ______________ to open the valve at the correct ______________ .

6. The coolant flow is from the ______________ to the lower hose, and then it is ______________ through the water jackets.

7. The coolant flow through most radiators is from the ______________ to the ______________ or from one ______________ to the other.



REVIEW QUESTIONS

8. Most modern vehicles use a(n) ______________ ______________ drive belt that is also called a(n) ______________ belt from the way that it is routed around the pulleys.

9. Cooling systems use a pressure cap in order to raise the ______________ ______________ of the ______________ .

10. As an engine warms up to operating temperature, coolant will flow past the pressure cap to the ______________ ______________ ______________ .

11. Do not remove the pressure cap of a hot system because the coolant will probably ______________ ______________ .

12. A fan clutch helps reduce fan ______________ ______________ and ______________ when a high airflow is not needed.

13. An electric fan can be mounted in front of the radiator and ______________ the air through it or behind the radiator and ______________ the air through.

14. The ideal coolant mix for most vehicles is ______________ antifreeze and ______________ water.

15. Dirty coolant is a sign that the ______________ should be ______________ .



CHAPTER QUIZ

1. Modern cooling systems are designed to maintain an engine temperature of ______________ .

a. 150 to 270°F

b. 100 to 160°F

c. 180 to 230°F

d. 170 to 300°F



CHAPTER QUIZ

2. Two students are discussing thermostats and coolant circulation. Student A says that the coolant does not circulate while the thermostat is closed. Student B says that the heater doesn’t blow warm air while the engine is cold because of this. Who is correct?

a. A only

b. B only

c. Both A and B

d. Neither A nor B



CHAPTER QUIZ

3. While discussing cooling system operation, Student A says that the engine will overheat if the thermostat sticks in the open position. Student B says that heater operation will be affected if the thermostat sticks open. Who is correct?

a. A only

b. B only

c. Both A and B

d. Neither A nor B



CHAPTER QUIZ

4. On most engine blocks, the coolant flow is into the ______________ .

a. top and out the bottom

b. top and out the top

c. bottom and out the top

d. bottom and out the bottom



CHAPTER QUIZ

5. Two students are discussing coolant circulation. Student A says that coolant flows from the bottom to the top in older radiator designs. Student B says that the coolant flows from one side of the radiator to the other in a crossflow design. Who is correct?

a. A only

b. B only

c. Both A and B

d. Neither A nor B



CHAPTER QUIZ

6. The boiling point of water with a 15-psi pressure cap is about ______________ .

a. 212°F

b. 290°F

c. 250°F

d. 300°F



CHAPTER QUIZ

7. The amount of power required to drive a fan is affected by the ______________ .

a. Diameter

b. blade pitch

c. number of blades

d. All of these



CHAPTER QUIZ

8. Two students are discussing fan clutches. Student A says that some fan clutches have a thermostatic valve that allows the clutch to drive the fan when it gets hot. Student B says that a fan clutch allows a large fan to be used with a lower noise level and power loss. Who is correct?

a. A only

b. B only

c. Both A and B

d. Neither A nor B



CHAPTER QUIZ

9. An electric cooling system fan is controlled by ______________ .

• a. cooling system temperature• b. A/C system operation• Which is correct?

a. A only

b. B only

c. Both A and B

d. Neither A nor B



CHAPTER QUIZ

10.The best amount of ethylene glycol to mix into the coolant is ______________ .

a. 25%

b. 50%

c. 75%

d. 100%

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Always Learning. CHAPTER 17 Cooling System Theory