Cooling System

Car Engine Pictures

Diagram of a cooling system: how the plumbing is connected. Want Want to learn more? Check out these car engine pictures. pictures. HW

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How Car Computers Work 

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How Car Engines Work 

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How does a car!s cooling system thermostat work?

"lthough gasoline engines engines ha#e  ha#e impro#ed a lot$ they are still not #ery efficient at turning chemical energy into mechanical power. %ost of the energy in the gasoline &perhaps '()* is con#erted into heat$ and it is the +ob of the cooling system  to take care of that heat. ,n fact$ the cooling system on a car dri#ing down do wn the freeway dissipates enough heat to heat h eat two a#eragesied houses/ 0he primary +ob of the cooling s ystem is to keep the engine from o#erheating by transferring this heat to the air$ but the cooling system also has se#eral other important +obs. 0he engine in your car runs best at a fairly high temperature. When the engine is cold$ components wear out faster$ and the engine is less efficient and emits more pollution. o another important +ob of the cooling system is to allow the engine to heat up as 1uickly as possible$ and then to keep the engine at a constant temperature

The Basics ,nside your car!s engine$ fuel is constantly burning. " lot of the heat from this combustion goes right out the e2haust system$ but some of it soaks into the engine$ heating it up. 0he engine runs  best when its coolant is about 3(( degrees 4ahrenheit &56 degrees Celsius*. "t this temperature: •

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0he combustion chamber is hot enough to completely #aporie the fuel$ pro#iding better combustion and reducing emissions. 0he oil used to lubricate the engine has a lower #iscosity &it is thinner*$ so the engine  parts mo#e more freely and the engine wastes less power mo#ing its own components around. %etal parts wear less.

0here are two types of cooling systems found on cars: li1uid-cooled and air-cooled.

Liquid Cooling 0he cooling system on li1uid-cooled cars circulates a fluid through pipes and passageways in the engine. "s this li1uid passes through the hot engine it absorbs heat$ cooling the engine. "fter the fluid lea#es the engine$ it passes through a heat e2changer$ or radiator$ which transfers the heat from the fluid to the air blowing through the e2changer.

Air Cooling ome older cars$ and #ery few modern cars$ are air-cooled. ,nstead of circulating fluid through the engine$ the engine block is co#ered in aluminum fins that conduct the heat away from the cylinder. " powerful fan forces air o#er these fins$ which cools the engine by transferring the heat to the air. ince most cars are li1uid-cooled$ we will focus on that system in this article

Click on "Start" to see the fluid flo through the engine as the engine arms up!

lum#ing

0he cooling system in your car has a lot of plumbing. We!ll start at the pump and work our way through the system$ and in the ne2t sections we!ll talk about each part of the system in more detail. 0he pump sends the fluid into the engine #lock $ where it makes its way through passages in the engine around the cylinders. 0hen it returns through the cylinder head  of the engine. 0he thermostat  is located where the fluid lea#es the engine. 0he plumbing around the thermostat sends the fluid back to the pump directly if the thermostat is closed. ,f it is open$ the fluid goes through the radiator  first and then back to the pump. 0here is also a separate circuit for the heating system. 0his circuit takes fluid from the cylinder head and passes it through a heater core and then back to the pump. 7n cars with automatic transmissions$ there is normally also a separate circuit for coo ling the transmission fluid built into the radiator. 0he oil from the transmission is pumped by the transmission through a second heat e2changer inside the radiator 

$luid Cars operate in a wide #ariety of temperatures$ from well below freeing to well o#er 8(( 4 &69 C*. o whate#er fluid is used to cool the engine has to ha#e a #ery low freeing point$ a high  boiling point$ and it has to ha#e the capacity to hold a lot of heat. Water is one of the most effecti#e fluids for holding heat$ but water freees at too high a temperature to be used in car engines. 0he fluid that most cars use is a mi2ture of water and ethylene glycol &C3H73*$ also known as antifreee. ;y adding ethylene glycol to water$ the  boiling and freeing points are impro#ed significantly.

$luid % $ree&ing oint % Boiling oint •

Pure Water: ( C < 63 4 - 8(( C < 383 4

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=(<=( mi2 of C3H73
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'(<6( mi2 of C3H73
0he temperature of the coolant can sometimes reach 3=( to 3'= 4 &838 to 86= C*. E#en with ethylene glycol added$ these temperatures would boil the coolant$ so something additional must  be done to raise its boiling point. 0he cooling system uses pressure to further raise the boiling point of the coolant. >ust as the  boiling temperature of water is higher in a pressure cooker$ the boiling temperature of coolant is higher if you pressurie the system. %ost cars ha#e a pressure limit of 8 to 8= pounds per s1uare inch &psi*$ which raises the boiling point another = 4 &3= C* so the coolant can withstand the high temperatures.

"ntifreee also contains additi#es to resist corrosion

'ater ump " centrifugal pump like the one used in your car. 0he water pump is a simple centrifugal pump dri#en by a belt connected to the crankshaft of the engine. 0he pump circulates fluid whene#er the engine is running. 0he water pump uses centrifugal force to send fluid to the outside while it spins$ causing fluid to  be drawn from the center continuously. 0he inlet to the pump is located near the center so that fluid returning from the radiator  hits the pump #anes. 0he pump #anes fling the fluid to the outside of the pump$ where it can enter the engine. 0he fluid lea#ing the pump flows first through the engine block and cylinder head$ then into the radiator and finally back to the pump

Note that the alls of the cylinder are quite thin( and that the engine #lock is mostly hollo!

)ngine 0he engine block and cylinder head ha#e many passageways cast or machined in them to allow for fluid flow. 0hese passageways direct the coolant to the most critical areas of the engine. 0emperatures in the combustion chamber of the engine can reach $=(( 4 &3$=(( C*$ so cooling the area around the cylinders is critical. "reas around the e2haust #al#es are especially crucial$ and almost all of the space inside the cylinder head around the #al#es that is not needed for

structure is filled with coolant. ,f the engine goes without cooling for #ery long$ it can seie. When this happens$ the metal has actually gotten hot enough for the piston to weld itself to the cylinder. 0his usually means the complete destruction of the engine.

The head of the engine also has large coolant passageays!

7ne interesting way to reduce the demands on the cooling system is to reduce the amount of heat that is transferred from the combustion chamber to the metal parts of the engine. ome engines do this by coating the inside of the top of the cylinder head with a thin layer of ceramic . Ceramic is a poor conductor of heat$ so less heat is conducted through to the metal and more passes out of  the e2haust

Picture of radiator showing side tank with cooler.

*adiator " radiator is a type of heat exchanger . ,t is designed to transfer heat from the hot coolant that flows through it to the air blown through it b y the fan.

%ost modern cars use aluminum radiators. 0hese radiators are made by braing thin aluminum fins to flattened aluminum tubes. 0he coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. 0he fins con duct the heat from the tubes and transfer it to the air flowing through the radiator. 0he tubes sometimes ha#e a type of fin inserted into them called a tur#ulator $ which increases the turbulence of the fluid flowing through the tubes. ,f the fluid flowed #ery smoothly through the tubes$ only the fluid actually touching the tubes would be cooled directly. 0he amount of heat transferred to the tubes from the fluid running through them depends on the difference in temperature between the tube and the fluid touching it. o if the fluid that is in contact with the tube cools down 1uickly$ less heat will be transferred. ;y creating turbulence inside the tube$ all of the fluid mi2es together$ keeping the temperature of the fluid touching the tubes up so that more heat can be e2tracted$ and all of the fluid inside the tube is used effecti#ely. @adiators usually ha#e a tank on each side$ and inside the tank is a transmission cooler. ,n the  picture abo#e$ you can see the inlet and outlet where the oil from the transmission enters the cooler. 0he transmission cooler is like a radiator within a radiator$ e2cept instead of e2changing heat with the air$ the oil e2changes heat with the coolant in the radiator 

ressure Cap 0he radiator cap actually increases the boiling point of your coolant by about = 4 &3= C*. How does this simple cap do this? 0he same way a pressure cooker increases the boiling temperature of water. 0he cap is actually a pressure release #al#e$ and on cars it is usually set to 8= psi. 0he  boiling point of water increases when the water is placed under pressure. When the fluid in the cooling system heats up$ it e2pands$ causing the pressure to build up. 0he cap is the only place where this pressure can escape$ so the setting of the spring on the cap determines the ma2imum pressure in the cooling system. When the pressure reaches 8= psi$ the  pressure pushes the #al#e open$ allowing coolant to escape from the cooling system. 0his coolant flows through the o#erflow tube into the bottom of the o#erflow tank. 0his arrangement keeps air  out of the system. When the radiator cools back down$ a #acuum is created in the cooling system that pulls open another spring loaded #al#e$ sucking water back in from the bottom of the o#erflow tank to replace the water that was e2pelled

0he open and closed positions of a thermostat. HW

Thermostat 0he thermostat!s main +ob is to allow the engine to heat up 1uickly$ and then to keep the engine at a constant temperature. ,t does this by regulating the amount of water that goes through the radiator. "t low temperatures$ the outlet to the radiator is completely blocked -- all of the coolant is recirculated back through the engine. 7nce the temperature of the coolant rises to between 89( and 85= 4 &93 - 58 C*$ the thermostat starts to open$ allowing fluid to flow through the radiator. ;y the time the coolant reach es 3(( to 389 4 &56 - 8(6 C*$ the thermostat is open all the way. ,f you e#er ha#e the chance to test one$ a thermostat is an amaing thing to watch because what it does seems impossible. Aou can put one in a pot of boiling water on the sto#e. "s it heats up$ its #al#e opens about an inch$ apparently by magic/ ,f you!d like to try this yourself$ go to a car parts store and buy one for a couple of bucks. 0he secret of the thermostat lies in the small cylinder located on the engine-side of the de#ice. 0his cylinder is filled with a wa2 that begins to melt at around 89( 4 &different thermostats open at different temperatures$ but 89( 4 is a common one*. " rod connected to the #al#e presses into this wa2. When the wa2 melts$ it e2pands significantly$ pushing the rod out of the cylinder and opening the #al#e. ,f you ha#e read How 0hermometers Work  and done the e2periment with the  bottle and the straw$ you ha#e seen this process in action -- the wa2 +ust e2pands a good bit more  because it is changing from a solid to a li1uid in addition to e2panding from the heat. 0his same techni1ue is used in automatic openers for greenhouse #ents and skylights. ,n these de#ices$ the wa2 melts at a lower temperature

Cooling fan

$an Bike the thermostat$ the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature. 4ront-wheel dri#e cars ha#e electric fans  because the engine is usually mounted trans#ersely$ meaning the output of the engine points toward the side of the car. 0he fans are controlled either with a thermostatic switch or by the engine computer$ and they turn on when the temperature of the coolant goes abo#e a set point. 0hey turn back off when the temperature d rops below that  point. @ear-wheel dri#e cars with longitudinal engines usually ha#e engine%dri+en cooling fans . 0hese fans ha#e a thermostatically controlled #iscous clutch. 0his clutch is positioned at the hub of the fan$ in the airflow coming through the radiator. 0his special #iscous clutch is much like the #iscous coupling sometimes found in all-wheel dri#e cars

,eater plum#ing

,eating System Aou may ha#e heard the ad#ice that if you car is o#erheating$ open all the windows and run the heater with the fan going at full blast. 0his is because the heating system is actually a secondary cooling system that mirrors the main cooling system on your car. 0he heater core$ which is located in the dashboard of your car$ is really a small radiator. 0he heater fan blows air through the heater core and into the passenger compartment of your car.

A heater core looks like a small radiator!

0he heater core draws its hot coolant from the cylinder head and returns it to the pump -- so the heater works regardless of whether the thermostat is open or c losed. 4or more information on car cooling systems and related topics$ check out the links on the ne2t  page