Cooling System Pt. 2

Water Pump

  • The engine-driven water pump is a centrifugal pump that circulates coolant through the engine block, cylinder head, intake manifold, hoses, and radiator.

  • It is typically driven by a belt connected to the crankshaft pulley but can also be gear-driven directly off the crankshaft sprocket and timing chain.

Major Parts of a Typical Water Pump

  • Water pump impeller: A disk with fan-like blades that spins to create pressure and flow. It can be made of steel or plastic, with curved or straight blades.

    • Straight blades (paddle wheels) are sometimes used to reduce engine power consumption.

  • Water pump shaft: A steel shaft that transmits turning force from the hub to the impeller.

  • Water pump seal: Prevents coolant from leaking between the pump shaft and housing.

  • Water pump bearings: Plain or ball bearings that allow the pump shaft to spin freely within the housing.

  • Water pump hub: Provides a mounting point for the belt pulley and fan.

  • Water pump housing: An iron or aluminum casting that forms the main body of the pump.

  • Water pump gasket: A gasket that fits between the engine and pump housing to prevent coolant leakage. RTV sealer or a rubber seal may also be used.

  • The water pump is usually mounted on the front of the engine. In transverse engines, it may bolt to the side and extend towards the front.

Water Pump Operation

  • The spinning crankshaft pulley turns the water pump pulley, shaft, and impeller.

  • Coolant trapped between the impeller blades is thrown outward by centrifugal force, creating:

    • Suction (vacuum) in the central area of the pump housing.

    • Pressure in the outer area of the housing.

  • The pump inlet is near the center, so coolant is pulled from the radiator, through the lower hose, and into the pump.

  • The pressurized coolant flows into the engine, circulates through the block, around the cylinders, up through the cylinder head(s), through the thermostat, and back into the radiator.

Electric Water Pump

  • Uses a large DC motor and an impeller to force coolant through the engine's water jackets or the HV cooling system.

  • Replaces a belt-driven water pump.

  • Often bolts to the side of the engine and has one radiator hose connected to it.

  • The engine control unit (ECU) energizes the electric water pump when the engine reaches a predetermined operating temperature to maintain the correct engine temperature.

  • Benefits:

    • Allows the engine to reach operating temperature more quickly for improved efficiency.

    • The pump's speed can be controlled by the ECU to reduce energy consumption.

Radiator and Heater Hoses

  • Radiator hoses transport coolant between the engine water jackets and the radiator.

  • Their flexibility allows them to withstand engine vibrations without breaking.

  • The upper radiator hose typically connects the thermostat housing on the intake manifold or cylinder head to the radiator.

  • The lower hose usually connects the water pump inlet to the radiator.

  • Types of radiator hoses:

    • Molded hose: Manufactured in a specific shape to fit a particular vehicle model.

    • Flexible hose: Has an accordion shape, allowing it to bend to different angles without collapsing and blocking flow; also called a universal-type radiator hose.

  • A hose spring is often used inside the lower radiator hose to prevent it from collapsing under suction from the water pump.

    • Removing this spring can cause the hose to collapse and lead to engine overheating.

  • Heater hoses are small-diameter hoses that carry coolant to the heater core.

  • Hose clamps secure radiator and heater hoses to their fittings.

    • A worm-drive hose clamp is the most common type, using a worm gear to tighten the clamp around the hose.

Radiator

  • The radiator transfers heat from the coolant to the outside air.

  • It is typically mounted at the front of the engine where cool air can flow through it.

Radiator Components

  • Radiator core: The central section of the radiator, made of tubes and cooling fins soldered or bonded together. This is where heat transfer occurs.

  • Radiator tanks: Metal or plastic ends that fit over the core tube ends to provide storage for coolant and fittings for hoses.

    • They also have fittings for large coolant hoses and sometimes for transmission oil coolers.

  • Radiator filler neck: An opening for adding coolant that also holds a removable radiator pressure cap to prevent coolant from boiling above 212°F (100°C).

    • The filler neck has an overflow tube connected to the coolant reservoir tank.

  • Transmission oil cooler: An inner tank for cooling automatic transmission or transaxle fluid.

    • It is located inside the radiator tanks and has tube fittings for the metal cooler lines running to the transmission.

  • Radiator petcock: A fitting on the bottom of the tank for draining coolant.

  • Radiator cap: Pressurizes the coolant to prevent boiling above 212°F (100°C).

Radiator Action

  • Hot engine coolant circulates through the radiator tanks and core.

  • Heat is transferred into the core's tubes and fins.

  • Air flowing over the fins removes heat, reducing the coolant's temperature before it returns to the engine.

Radiator Types

  • Downflow radiator: Tanks are located at the top and bottom of the core, with core tubes running vertically.

    • Hot coolant enters the top tank and flows downward through the tubes.

  • Crossflow radiator: Tanks are on the sides of the core, with core tubes arranged for horizontal coolant flow.

    • The tank with the radiator cap is usually the outlet tank.

    • Allows for a lower hood line due to its shorter height.

  • Radiator tanks can be made of metal or plastic.

    • Metal tanks are soldered to the core.

    • Plastic tanks use rubber seals to prevent leakage.

Transmission Oil Cooler

  • Used in cars with automatic transmissions or transaxles to prevent the transmission fluid from overheating.

  • It is a small tank enclosed within one of the main radiator tanks.

  • Heat is removed from the hotter transmission fluid as it passes through the radiator and cooler.

  • Location:

    • Downflow radiators: in the lower tank.

    • Crossflow radiators: in the tank with the radiator cap.

  • Metal lines connect the automatic transmission or transaxle to the cooler fittings.

  • The transmission oil pump forces fluid through the lines and cooler.

Radiator Cap

  • Functions:

    • Seals the top of the radiator filler neck to prevent leakage.

    • Pressurizes the system to raise the boiling point of the coolant.

    • Relieves excess pressure to protect against system damage.

    • In closed systems, allows coolant flow between the radiator and the coolant reservoir.

  • Locks onto the radiator tank filler neck or the reservoir tank with airtight rubber or metal seals.

  • Can be made of metal or plastic.

Radiator Cap Pressure Valve

  • A spring-loaded disk that contacts the filler neck to form a seal.

  • Increasing pressure raises the boiling point of water.

    • For every pound of pressure increase, water's boiling point increases about 3°F (1.67°C).

  • Typical radiator cap pressure is 12-16 psi (83-110 kPa), raising the coolant boiling point to 250-260°F (121-127°C).

  • If the engine overheats and pressure exceeds the cap rating, the pressure valve opens, releasing excess pressure and steam into the reservoir.

Radiator Cap Vacuum Valve

  • Opens to allow flow back into the radiator when the coolant temperature drops after engine operation.

  • The cooling and contraction of the coolant and air in the system decreases the coolant volume and pressure.

  • Without a vacuum valve, radiator hoses and tanks could collapse from outside pressure.

Cooling System Fans

  • A cooling system fan pulls air through the radiator core and over the engine to help remove heat.

  • It increases the volume of air flowing through the radiator, particularly when the car is stationary.

  • Fans are driven by a fan belt or an electric motor.

Engine-Powered Fans

  • Bolts to the water pump hub and pulley.

  • A fan spacer may be used to position the fan closer to the radiator.

  • Types:

    • Flex fan: Has flexible blades that alter airflow with engine speed.

      • At low speeds, the curved blades pull air through the radiator.

      • At high speeds, the blades straighten to reduce fan action and save engine power.

    • Fluid coupling fan clutch: Designed to slip at higher engine speeds, similar to a flexible fan. It uses silicone-based oil.

    • Thermostatic fan clutch: Has a temperature-sensitive, bimetal spring that controls fan action by regulating oil flow in the clutch.

      • When cold, the clutch slips to speed engine warm-up.

      • After reaching operating temperature, the clutch locks for forced-air circulation.

Electric Cooling Fans

  • Uses an electric motor, a coolant temperature sensor, and the engine ECM to provide airflow and heat transfer out of the radiator.