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Introduction toRadiator andRadiator Caps

Radiator and Cooling System

Cooling System - Basics

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Inside your car's engine, fuel is constantly burning. A lotof the heat from this combustion goes right out theexhaust system, but some of it soaks into the engine,heating it up. The engine runs best when its coolant is

about 200 degrees Fahrenheit (93 degrees Celsius). Atthis temperature:

The combustion chamber is hot enough tocompletely vaporize the fuel, providing bettercombustion and reducing emissions

The oil used to lubricate the engine has a lowerviscosity (it is thinner), so the engine parts move

more freely and the engine wastes less powermoving its own components around.

Metal parts wear less.

There are two types of cooling systems found on cars:liquid-cooled and air-cooled.

Liquid Cooling

The cooling system on liquid-cooled cars circulates afluid through pipes and passageways in the engine. Asthis liquid passes through the hot engine it absorbs heat,cooling the engine. After the fluid leaves the engine, itpasses through a heat exchanger, or radiator, whichtransfers the heat from the fluid to the air blowingthrough the exchanger.

Air Cooling

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Some older cars, and very few modern cars, are air-cooled. Instead of circulating fluid through the engine,the engine block is covered in aluminum fins thatconduct the heat away from the cylinder. A powerful fan

forces air over these fins, which cools the engine bytransferring the heat to the air.

The Radiator Caps considered in this project work on theLiquid Cooling system , we will focus on that system

henceforth.

Radiator

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A radiator is a type of heat exchanger. It is designed totransfer heat from the hot coolant that flows through itto the air blown through it by the fan.

Most modern cars use aluminum radiators. Theseradiators are made by brazing thin aluminum fins toflattened aluminum tubes. The coolant flows from theinlet to the outlet through many tubes mounted in aparallel arrangement. The fins conduct the heat from thetubes and transfer it to the air flowing through theradiator.

The tubes sometimes have a type of fin inserted intothem called a turbulator, which increases the turbulenceof the fluid flowing through the tubes. If the fluid flowedvery smoothly through the tubes, only the fluid actuallytouching the tubes would be cooled directly. The amountof heat transferred to the tubes from the fluid runningthrough them depends on the difference in temperaturebetween the tube and the fluid touching it.

So if the fluid that is in contact with the tube cools downquickly, less heat will be transferred. By creatingturbulence inside the tube, all of the fluid mixestogether, keeping the temperature of the fluid touchingthe tubes up so that more heat can be extracted, and allof the fluid inside the tube is used effectively.

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Radiators usually have a tank on each side, and inside

the tank is a transmission cooler. In the picture above,you can see the inlet and outlet where the oil from thetransmission enters the cooler. The transmission cooleris like a radiator within a radiator, except instead ofexchanging heat with the air, the oil exchanges heatwith the coolant in the radiator.

Engine

The engine block and cylinder head have manypassageways cast or machined in them to allow for fluidflow. These passageways direct the coolant to the mostcritical areas of the engine.

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Note that the walls of the cylinder are quite thin, and that the

engine block is mostly hollow.

Temperatures in the combustion chamber of the enginecan reach 4,500 F (2,500 C), so cooling the area aroundthe cylinders is critical. Areas around the exhaust valvesare especially crucial, and almost all of the space insidethe cylinder head around the valves that is not neededfor structure is filled with coolant. If the engine goeswithout cooling for very long, it can seize. When thishappens, the metal has actually gotten hot enough for

the piston to weld itself to the cylinder. This usuallymeans the complete destruction of the engine.

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The head of the engine also has large coolantpassageways.

Radiator Cap (Pressure Cap)

The radiator cap actually increases the boiling point ofyour coolant by about 45 F (25 C). The radiator cap doesthis the same way a pressure cooker increases theboiling temperature of water. The cap is actually a

pressure release valve, and on cars it is usually set to 15psi. The boiling point of water increases when the wateris placed under pressure.

Working

When the fluid in the cooling system heats up, itexpands, causing the pressure to build up. The cap is theonly place where this pressure can escape, so the

setting of the spring on the cap determines themaximum pressure in the cooling system.

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Normal

When the pressure reaches 15 psi, the pressure pushesthe valve open, allowing coolant to escape from thecooling system. This coolant flows through the overflowtube into the bottom of the overflow tank. Thisarrangement keeps air out of the system. When theradiator cools back down, a vacuum is created in thecooling system that pulls open another spring loadedvalve, sucking water back in from the bottom of the

overflow tank to replace the water that was expelled.

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During Overheat

Parts of Radiator Cap

The main parts of the Radiator Cap are as follows:

Cover

Spring Washer

Main Valve

Retainer

Protector

Main Spring

Main valve Gasket

Neck Gasket

Protector Gasket

Vacuum Valve Gasket

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Critical functions of Radiator Cap

Other than those, the main functions of the radiator capsfor which they are considered to be the critical part of anengine cooling system is as follows:

Pressure relief valve to safely and harmlessly ventexcess pressure into the overflow jug thus keep thepressure in the safe working pressure range.

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To prevent overheating by pressurizing the systemto raise the boiling temperature of coolant andallow the automobile's engine to operate at moreefficient higher temperatures.

Prevents the evaporation of coolant and thus helpsus to operate the engine economically as it isexpensive.

Vacuum relief valve to draw coolant from theoverflow jug back into the radiator to prevent airfrom entering the system and allowing the coolantto perform its function more efficiently as the

coolant.

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