15-10-2014, 04:01 PM
AUTOMOTIVE INDUSTRY TRAINING
RETAIL, SERVICE AND REPAIR
1408007257-Inspect2020Service20Cooling20systems.pdf (Size: 885.03 KB / Downloads: 224)
Engine Cooling, Air-intake and Starting Systems
The cooling system in most cars consists of the radiator and water pump. Water circulates through
passages around the cylinders and then travels through the radiator to cool it off. In a few cars
(most notably Volkswagen Beetles), as well as most motorcycles and lawn mowers, the engine is
air-cooled instead (You can tell an air-cooled engine by the fins adorning the outside of each
cylinder to help dissipate heat.). Air-cooling makes the engine lighter but hotter, generally
decreasing engine life and overall performance. So now you know how and why your engine stays cool. But why is air circulation so important?
Most cars are normally aspirated, which means that air flows through an air filter and directly into
the cylinders. High-performance engines are either turbocharged or supercharged, which means
that air coming into the engine is first pressurized (so that more air/fuel mixture can be squeezed
into each cylinder) to increase performance. The amount of pressurization is called boost. A
turbocharger uses a small turbine attached to the exhaust pipe to spin a compressing turbine in the
incoming air stream. A supercharger is attached directly to the engine to spin the compressor. Increasing your engine's performance is great, but what exactly happens when you turn the key to
start it? The starting system consists of an electric starter motor and a starter solenoid. When you
turn the ignition key, the starter motor spins the engine a few revolutions so that the combustion
process can start. It takes a powerful motor to spin a cold engine. The starter motor must
overcome:
• All of the internal friction caused by the piston rings
• The compression pressure of any cylinder(s) that happens to be in the compression stroke
• The energy needed to open and close valves with the camshaft
• All of the "other" things directly attached to the engine, like the water pump, oil pump,
alternator, etc.
Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds
of amps of electricity must flow into the starter motor. The starter solenoid is essentially a large
electronic switch that can handle that much current. When you turn the ignition key, it activates the
solenoid to power the motor.
Engine Lubrication, Fuel, Exhaust and Electrical Systems
When it comes to day-to-day car maintenance, the first concern is probably the amount of
petroleum in your car. How does the petroleum that you put in power the cylinders? The engine's
fuel system pumps petroleum from a tank and mixes it with air so that the proper air/fuel mixture
can flow into the cylinders. Fuel is delivered in three common ways: carburetion, port fuel injection
and direct fuel injection.
In carburetion, a device called a carburettor mixes gas into air as the air flows into the engine. In a
fuel-injected engine, the right amount of fuel is injected individually into each cylinder either right
above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).
Oil also plays an important part. The lubrication system makes sure that every moving part in the
engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they
can slide easily in their cylinders) and any bearings that allow things like the crankshaft and
camshafts to rotate freely. In most cars, oil is sucked out of the oil pan by the oil pump, run through
the oil filter to remove any grit, and then squirted under high pressure onto bearings and the
cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle
repeats.
Now that you know about some of the stuff that you put in your car, let's look at some of the stuff
that comes out of it. The exhaust system includes the exhaust pipe and the muffler. Without a
muffler, what you would hear is the sound of thousands of small explosions coming out your
tailpipe. A muffler dampens the sound. The exhaust system also includes a catalytic converter.
The emission control system in modern cars consists of a catalytic converter, a collection of
sensors and actuators, and a computer to monitor and adjust everything. For example, the catalytic
converter uses a catalyst and oxygen to burn off any unused fuel and certain other chemicals in
the exhaust. An oxygen sensor in the exhaust stream makes sure there is enough oxygen
available for the catalyst to work and adjusts things if necessary.
Besides gas, what else powers your car? The electrical system consists of a battery and an
alternator. The alternator is connected to the engine by a belt and generates electricity to recharge
the battery. The battery makes 12-volt power available to everything in the car needing electricity
(the ignition system, radio, headlights, windshield wipers, power windows and seats, computers,
etc.) through the vehicle's wiring.
How Car Cooling Systems Work
Although petroleum engines have improved a lot, they are still not very efficient at turning chemical
energy into mechanical power. Most of the energy in the gasoline (perhaps 70%) is converted into
heat, and it is the job of the cooling system to take care of that heat. In fact, the cooling system on
a car driving down the freeway dissipates enough heat to heat two average-sized houses! The
primary job of the cooling system is to keep the engine from overheating by transferring this heat to
the air, but the cooling system also has several other important jobs.
The 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. So another important job
of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the
engine at a constant temperature.
The Basics
Inside your car's engine, fuel is constantly burning. A lot of the heat from this combustion goes
right out the exhaust 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). At this temperature:
• The combustion chamber is hot enough to completely vaporize the fuel, providing better
combustion and reducing emissions.
• The oil used to lubricate the engine has a lower viscosity (it is thinner), so the engine
parts move more freely and the engine wastes less power moving its own components
around.
• Metal parts wear less.
There are two types of cooling systems found on cars: liquid-cooled and air-cooled.
Plumbing
The 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 next sections we'll talk about each part of the system in more detail.
The pump sends the fluid into the engine block, where it makes its way through passages in the
engine around the cylinders. Then it returns through the cylinder head of the engine. The
thermostat is located where the fluid leaves the engine. The plumbing around the thermostat sends
the fluid back to the pump directly if the thermostat is closed. If it is open, the fluid goes through the
radiator first and then back to the pump.
There is also a separate circuit for the heating system. This circuit takes fluid from the cylinder
head and passes it through a heater core and then back to the pump.
Cars Cooling System Service
Since the colder months will soon be upon us, there are several things considered critical in your
vehicle's maintenance. And since the engine is the heart of your vehicle and directly affects its
operation, here is what you can do to ensure proper engine life and performance. A vehicle's
cooling system should be serviced seasonally to prevent premature engine wear due to extreme
climate or engine temperature.
According to Everco Industries, a leading manufacturer of automotive cooling system parts, one
sure way to prepare the engine's cooling system for these extreme climate conditions is to have
your local service dealer perform a few basic preventive maintenance checks during your next
routine servicing:
Check for external leaks. Usual areas of leakage are water manifolds, radiator seams,
water pumps, freeze plugs and all hose connections. The condition of radiator hoses should
be carefully scrutinized for possible deterioration from age and/or wear from rubbing
against accessory brackets, etc. Be aware that in many cases radiator hoses wear from the
inside out, so outside appearance can be deceiving.
2. Check for internal leaks. Pull the oil dipstick and check for evidence of coolant. It will
show up as minute droplets or sludge and should be easy to spot. This could indicate a
cracked head, block or blown head gasket.
3. Check the radiator. This is the one component in your vehicle's cooling system which can
quickly diminish the efficiency and durability of the engine. Check for obstructed air flow
and clean any debris from the fins. Also check the radiator mounting for loose bolts or
cracked brackets from vibration and stress.
4. Check the cooling fan. If the vehicle is equipped with a centrifugal thermo-static type fan
clutch, it is important to spot problems before they occur. Check for wear by moving the fan
blade back and forth. Over 1/4" of play in either direction could point towards excessive
bearing wear. You should also turn the fan by hand. If it free-wheels or there is a rough
grating feel as the fan turns, this could mean excessive fluid loss or bearing wear
respectively. If any of these conditions exist or there is evidence of fluid leakage, the fan
clutch should be replaced. If the vehicle is equipped with an electric cooling fan, a quick
performance check can be made by turning on the A/C and checking to make sure it
operates without excess vibration or noise. Also check all electrical connections for signs of
corrosion, or physical damage. With the engine hot, check to see if the fan is coming on at
the correct temperature and operating properly.
Check the coolant level and conditions. As a general rule the coolant level should be 1"
to 2" below the radiator filler neck when cool. Use an antifreeze tester to determine the
protection range of the coolant. It should be at least adequate for the geographic area
where you live. If the coolant is over two years old or has rust in it, system flushing and
refilling with new antifreeze solution is recommended and will be sufficient for most
climates. The two year replacement interval is necessary to maintain proper rust inhibitor
and other additive protection in the cooling system.
6. Check the radiator cap. If your cap is rusted or the rubber seal is dried out, it should be
replaced. A pressure tester should be used to be sure the cap is operating at the
recommended pressure level.
7. Check the thermostat. Remove the radiator cap and start the engine. Insert a suitable
thermometer into the radiator neck. When the coolant level drops in the radiator, the
thermostat has opened and is allowing circulation. Record the temperature on the
thermometer and compare to the thermostat specifications. It should be no more than a few
degrees either way of the actual thermostat setting. If you are not in the correct range, the
thermostat will have to be replaced. Be sure to install a new gasket and inspect the
thermostat seating area for corrosion and pitting.