Engine Cooling Systems

1. Engine Cooling Systems • This presentation will explore: • Cooling Systems • Cooling System Components • Fans • Coolant Characteristics

2. Air or Water Air cooling requires a large volume of air flow around the engine. Air cooling The cylinder has cooling fins to improve radiation of heat. The large surface area of the fins, transfers heat to the surrounding air. With water cooling, the coolant circulates around a water jacket to absorb the heat energy. The coolant is a mixture of water and antifreeze and anticorrosion additives. Water cooling Water cooling provides better control and stability of the engine temperature.

3. Cooling System Combustion temperatures in the cylinders can reach 2500ºC (4500ºF). If uncontrolled, these high temperatures can cause damage to the engine. Normal coolant operating temperatures are about 80-100ºC (180-210ºF). Coolant absorbs heat energy in the cylinder by conduction, radiating the excess heat to the air by use of the radiator. The rate of air flow over the radiator may be increased by the use of a fan.

4. Water Pump The water pump forces coolant through the engine cylinder block and head channels. Seal Leak bore Drive pulley Impeller Coolant is drawn into the centre of the water pump via the lower hose of the radiator. Centrifugal force, due to the rotation of the water pump impeller, throws the liquid out at the edge and into the cylinder block. Main shaft Water pump housing If a mechanical cooling fan is used, it may often be attached to the water pump hub. Bearings

5. Water Flow Pipes to passenger compartment heater Conventional coolant flow is upward past the cylinders (hot liquid rises). Water cooled inlet system Coolant then flows out from the cylinder head to the radiator via its top hose. The hot coolant is then cooled as it travels through the radiator. To top hose Thermostat housing The water pump draws coolant from the bottom of the radiator and forces it back through the cylinder block. Reverse flow cooling is unusual, but is in the opposite direction from that described above. From bottom hose Coolant flow around cylinders

6. Radiator Coolant flow within engine Radiator hoses The function of the radiator is to transfer unwanted heat energy from the coolant to the outside air. Hoses connect the radiator to the engine cylinder block (water jacket) and passenger compartment heater. Fan(s) draw air through and over the radiator to increase the air flow and improve cooling efficiency. Pump Fan A thermostat controls the coolant flow during warm-up, so that the engine reaches operating temperature quickly. Cross flow radiator

7. Thermostat Closed When the engine is cold, the thermostat is closed. A return spring holds the diaphragm against the aperture. To top hose and radiator The route to the radiator via the top hose is cut off by the closed thermostat. A by-pass channel returns the coolant to the water pump and allows it to circulate through the water jacket in the engine block and head. This cycle repeats until the optimum engine temperature is reached. This accelerates the engine warm-up process to both reduce engine wear and emissions. By-pass open

8. Thermostat Open To top hole As the engine and coolant warms up, a wax-filled pellet expands in the thermostat and pushes the thermostat open, closing theby-pass port. To top hose and radiator Coolant is allowed through to the radiator and then back to the engine. This continuing process allows the engine temperature to be maintained at its optimum value, and the thermostat will continue to cycle as temperatures rise and fall. By-pass closed

9. Downflow Radiators Tanks at the top and bottom of the radiator act as reservoirs for the coolant. Coolant flows down through the core tubes, which have cooling fins attached, allowing heat energy to be dissipated. The coolant flows out of the bottom tank back to the engine via the water pump. In vehicles with automatic transmission, oil coolers are often placed in the bottom tank of the radiator, enabling transmission oil to be cooled.

10. Crossflow Radiators Crossflow radiators are typically used in modern vehicles, as they allow low engine compartments and lower bonnet line. The reservoir tanks are found on each side of a crossflow radiator. The core tubes carrying the coolant, run horizontally. For vehicles with automatic transmission, the oil cooler is in the return tank (shown on the right in the diagram).

11. Hoses Flexible rubber hoses carry the coolant between the radiator, engine block and heater core. As they are flexible, they allow for engine vibrations without damage to the components. The upper hose carries water to the radiator from the cylinder head. The lower hose connects the radiator back to the water pump. Smaller hoses carry hot coolant to the passenger compartment heater. An expansion tank reservoir is used to keep the system topped up.

12. Types of Hoses There are a number of different types and materials of radiator hose, ranging from natural rubber construction to high temperature resistant silicone types. Moulded hoses are typically pre-formed for a particular make and model of vehicle. Moulded hose The construction of the hose, by useof materials such as synthetic yarn,styrene rubber or synthetic materials,provides a tough yet flexible hose capable of resisting coolant, abrasion, flexing, ultraviolet and dilute acids, which may degrade the hose over time. Flexible hose A support spring is sometimes fitted inside the radiator hose to prevent it collapsing under low pressure when the engine is cold.

13. RadiatorCap The radiator pressure cap pressurizes the coolant system in order to raise the coolant’s boiling point to about 125ºC (255ºF), this overcomes the production of steam. The pressure valve opens when the coolant system temperature rises significantly, to allow the escape of excess coolant to an expansion bottle. The surplus coolant is released and held in an expansion tank (in a closed system). Or in older vehicles, spills to the ground (in an open system).

14. Closed Cooling System The radiator top tank is connected via the pressure cap to an expansion tank. When the engine is hot, excess coolant flows to the expansion tank. When the engine cools, a vacuum valve in the pressure cap opens to allow the coolant to flow back to the radiator top tank.

15. Engine-Powered Fan Mechanical fans provide air flow across the radiator core tubes and may be bolted to the water pump hub. Belt pulley A spacer may be needed in order to place the fan near to the radiator. The blades of the fan may be flexible or fixed. Fluid coupling fan clutches are arranged to slip at higher speeds when natural air flow is likely to be increased. Thermostatic fan clutches slip at cold temperatures, reducing air flow through the radiator and speed warm-up. When the coolant reaches the operating temperature, the clutch locks and the fan rotates in a fixed manner.

16. Electric Cooling Fan Electric fans use DC (direct current) motors coupled to a thermostat switch. The fan is operated to prevent overheating when the coolant’s temperature increases beyond its optimum value. Temperature sending unit At low temperature: • Low temperature is indicated on the gauge, • The thermostat switch is open so there is no current feeding the motor. At high temperature: • High temperature indication on the gauge, • Thermostat switch is closed, Thermostat switch • Current feeds the fan motor.

17. Antifreeze At sea level the temperature range for water to remain as a liquid is from 0º-100ºC (32º-212ºF). Boiling With the engine coolant system pressurized, the boiling point is raised to about 125ºC (255ºF). The main disadvantages of using water in the coolant system is that it can freeze in winter conditions, and cause corrosion. Therefore, to prevent this, antifreeze (Ethylene Glycol) is added to the water in order to lower its freezing point to about-37ºC (-34ºF), in the case of a 50% mix. Freezing Other advantages of antifreeze are: • Prevents winter freezing • Resists rust and corrosion • Lubricates the water pump