Automotive Cooling Systems

Automotive
Cooling Systems Basics

The internal combustion engine generated a tremendous amount of heat. This heat is created when the air/fuel mixture is ignited and expands inside the engine combustion chamber. Temperatures can run as high as 1,000^o F (537.7^o C).

Cooling Systems

In a liquid-cooled system heat is removed from around the combustion chamber by a heat-absorbing liquid (coolant) circulating inside the engine. This liquid is pumped through the engine and, after absorbing the heat of combustion, flows into the radiator where the heat is transferred to the outside air. This system keeps engine temperature within a range where they provide the best performance.

Coolant

Engine coolant is actually a mixture of water and anifreeze/coolant. The typical recommended mixture is a 50/50 solution of water and antifreeze/coolant. Regardless of the mixture of the coolant or the type of antifreeze used, some lime, rust and scale will always build in a cooling system. For this reason and others, the engine's coolant should be replaced and the cooling system flushed every one or two years.

Thermostat

The thermostat controls the minimum operating temperature of the engine. The maximum operating temperature is controlled by the amount of heat being produced by the engine at the time and the cooling system's ability to dissipate the heat.
The most common location of the thermostat is at the front of the engine block. Thermostat fits into a recess in the block where it is exposed to hot coolant.
The thermostat permits fast warm-up of the engine. Slow warm-up causes moisture condensation in the combustion chambers, which finds its way into the crankcase and cause sludge formation.
Thermostats must start to open at a specified temperature, normally 3^o F(1.6^o C) above or below its temperature rating. It must be fully open at about 20⁰ F (1.6⁰ C) abouve the start-open temperature.

Water Pump

The heart of the cooling system is the water pump. It job is to move the coolant though the cooling system.
Usually the water pump is driven by the crankshaft through pulleys and a drive V-belt.
Water pumps are centrifugal-type pumps with a rotating paddle-wheel-type impeller to move the coolant.
When the engine is started, the impeller pushes the coolant from its pumping cavity into the engine block.
When the engine is cold, the thermostat is closed. The coolant stops before reaching the radiator.

In order for the water

pump to circulate the coolant through the engine during warm-up, a bypass passage is added below the thermostat.

Radiator Pressure Cap

The radiator car was at one time designed to keep the coolant from splashing out while providing a means to fill the radiator with coolant.
Now, radiator caps are equipped with pressure springs and vents. The cap allows for an increase in pressure in the radiator, which raises the boiling point of the coolant.

For every pound of pressure put on the coolant, the boiling point is raised about 3 1/4^oF (1.8^oC). Today's caps normally are designed to hold between 14 and17 psi (96.35 and 117.21 kPa). When the pressures exceed this level, the seal between the cap and the radiator filler neck opens and allows the excessive pressure to vent into the coolant recovery tank.

Expansion Tank

Most cooling systems have an expansion or recovery tank. Expansion tanks are designed to catch and hold any coolant that passes through the pressure cap when the engine is hot. As the engine warms up, the coolant expands. This eventually causes the pressure cap to release. The coolant passes to an expansion tank.
When the engine is shut down, the coolant begins to shrink. The vacuum spring inside the pressure cap opens and the coolant in the expansion tank is drawn back into the cooling system.
The marks on the recovery tank show where coolant levels should be when the car is running and when it is not.

Hoses

Coolant flows from the engine to the radiator and from the radiator to the engine through hoses. The radiator is solidly mounted to the vehicle and the engine sits on rubber mounts, which means the engine can move independently of the chassis and the radiator cannot. If the engine were connected solidly to the radiator, the radiator would soon break because of the vibration and stress.
Hoses connecting the engine to the radiator are made up of three parts, an inner rubber tube, some reinforcement material, and an outer rubber cover.
Cooling system hoses must be able to endure heavy vibrations and be resistant to oil, heat, abrasion, weathering, and pressure.
Most vehicles have at least four hoses in the cooing system.

Hose Clamps

Hoses are attached to the engine and radiator with clamps. Hose clamps are designed to apply clamping pressure around the outside of the hose at the point where it connects to the inlet and outlet connection at the radiator, engine block, water pump, or heater core.

Belt Drive

Belt drives have been used for many year. V-belts and V-ribbed (serpentine belts are used to drive water pumps, power steering pumps, air-conditioning compressors, generators, and emission control pumps.
Because the belts are flexible, they absorb some shock loads and cushion shaft bearing from excessive loads.
Belt drives can be used to drive a single part or a combination of parts. V-belts are typically used to drive a single component.

Most late model vehicles use a serpentine belt to drive accessories. Serpentine belts are used to drive all or most accessories.

Cooling Fans

At highway speeds, the ram air through the radiator should be sufficient to maintain proper cooling of the engine. However, at low speeds and idle, the system needs additional air. This air is delivered by fan. The fan may be driven by the engine, via a belt, or by an electric motor. To eliminate power drain during time when fan operation is not needed. This is accomplished by a fan clutch.

In most cars of today, to save power and reduce the noise level, the conventional belt-driven, water pump mounted engine cooling fan has been replaced with an electrically driven fan. The fan is mounted to the radiator shroud and are not connected mechanically or physically to the engine.

The 12 volt motor driven fan is electrically controlled by an engine coolant temperature switch or sensor and the air-conditioner switch. In most newer car it is controlled by the engine control computer.

Automotive Cooling Systems Basics