Chapter 39 Cooling System Fundamentals

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

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

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

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

Cooling System

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

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

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

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

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

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

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

Air Cooling Versus Liquid Cooling

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

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

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

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

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

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

Coolant Flow

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

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

Radiator and Heater Hoses

Two basic types of radiator hoses

Three basic types of hose clamps

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

Radiator Types Downflow Crossflow

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

Radiator Cap

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)

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

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

Pressure Cap Operation Hot engine

Pressure Cap Operation Cold engine

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

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

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

A temperature-sensitive valve Thermostat A temperature-sensitive valve

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

Thermostat Operation A. Cold engine B. Hot engine

Thermostat Operation Cold engine

Thermostat Operation Hot engine

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

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

Protected with antifreeze Corrosion Protection Protected with antifreeze Water only

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