Your cooling system works by pumping coolant(water and antifreeze)
through the engine where it absorbs heat, through the radiator (where it
loses that heat) and back into the engine.
Main components of the cooling system.
It can be plain water. Adding Glycol based antifreeze is definately
recommended as it not only raises the boiling point of the water and
lowers the freezing point but also contains very important corrosion
inhibitors. Adding too much antifreeze lowers the coolant's effectiveness so don't go more than a 50/50 mix unless stated otherwise by the manufacturer.
- Radiator. This acts as a heat exchanger
between the coolant and outside air. It is actually a whole bunch of
small pipes that have thin pieces of metal conncted to them to increase
the effective surface area.
- Waterpump. Well that's what it is. A pump to circulate the coolant around the engine.
This unit regulates the flow of coolant around the system. You need to
get the engine to operating temperature as quick as possible, then you
need to keep it there as this aids in lowering fuel consumption and
emissions and this is the job of the thermostat. It is installed in the
system in such a way that it can block the flow of coolant between the
radiator and the engine.
- Cooling fan. Cooling fans
help airflow through the radiator at low speed or when the vehicle is
stationary This may be electrical - powered by a thermostatic switch
and a relay, directly driven by a belt off the crankshaft or have a
viscous coupling. The viscous coupling is also directly driven but
contains a fluid which couples the fan to the pulley only when needed.
Reasons for overheating :
- Insufficient coolant
- Insufficient circulation of the coolant
- Insufficient airflow
- Excess heat generation
Do's and dont's
topping up it is better to use antifreeze only, as you will not
be diluting the mixture. When refilling use the correct mix of water
and antifreeze or fill with pre-mixed coolant.
Replace coolant according to service schedule.
Never open a hot cooling system.
The first and most obvious thing to check is coolant level.
reservoir : coolant is added directly to the radiator. Fill to the top.
You may find a little fluid missing everytime you open the radiator.
This is due to water expanding when heated which escapes through the
overflow pipe at the radiator cap.
Non pressurised reservoir. This
coolant tank is not pressurised and can be opened at any time. Usually
has a cap that just clips on. Fill to the max mark when the engine is
hot or at least to the min mark when the engine is cold. If this
reservoir is filled it does not nescesarily mean the system is full
since it depends on expansion and contraction of air and coolant within
the system to get coolant back into the radiator. The radiator should be
filled as well.
Pressurised reservoir : Most modern-day vehicles
are fitted with this type of system. It is pressurised and should only
be opened when the engine has cooled down. Do not overfill, always keep
coolant levels between the minimum and maximum marks.
If coolant levels keep dropping with no visible signs of leaking have the engine tested for a blown head gasket.
internal passageways that allow for coolant flow through the engine are
metal and constantly exposed to coolant which causes rust which is
transported throughout the system. The radiators' internal pipes have
very small diameters and easily become blocked by this rust. This
decreases the effective area of the radiator and the amount of water
that can pass through it. Regular replacement of the coolant will
prevent this build-up.
Waterpump impellers may break and decrease the efficiency of the pump although this is rare.
slipping fan belt will also cause decreased coolant flow but is usually
quite noticeable as a high pitched shrieking noise especially on
startup and when revving the engine.
The thermostat is in effect a
valve which opens and closes with temperature. They go faulty mostly
because of rust and scale buildup and can get stuck in a closed or
half-open position, thereby blocking waterflow to the radiator.
radiator fins are spaced closely together so can easily catch debris
such as bugs and grass which will impede airflow through the radiator.
The fan assists with airflow so if not working will see the engine
overheat when stationary or in stop-start traffic. If the engine cools
down while driving above 35mph this is the obvious starting point.
fuel/air mixture and incorrect ignition timing may cause the engine to
generate heat in exess of the coolings systems' capabilities.
How to test and repair :
- Check the fluid level. Also check for leaks. They will usually show up as brown or green streaks of dried coolant.
your fan belt/serpentine belt - is it still intact? Check the operation
of the fan. On a direct coupling you should not be able to move the
fan. A viscous coupling should not spin freely by more than a quarter
turn. See below for the electrical fan.
the system. Remove the upper and lower radiator hoses and if possible,
remove the radiator. Stick a hosepipe into the outlet side of the
radiator and let the water run until it comes out clear on the other
side. Then repeat the process with the hosepipe in the inlet side.
Continue with this until the water runs absolutely clear.Now remove the
thermostat from the engine and do the same to the engine. Clear the
radiator fins of bugs and debris.
- Check the
thermostat. It should be in the closed position. Drop it in a cup of
boiling water and you will notice it opening. Since it is already out
you may as well replace it since it is relatively inexpensive
an electric radiator fan, let the vehicle heat up to just before
overheating. If by this time the fan has not come on switch off the
engine.Locate the cooling fan fuse and check that it is intact. Using a
multimeter, measure between each of its' contacts and earth. See
diagram. Measure between 1 and earth(bare metal point on vehicle body or
on battery negative), and then between 2 and earth. Both readings
should be 12V or more with the ignition on. If 1 reading is found only,
the fuse is faulty. If no reading is found the wiring between the
ignition and fuse is faulty.
check the operation of the fan itself. Disconnect the fan. Connect a
lead wirefrom the battery negative to one of the fan connector pins and
from thebattery positive to the other pin. See diagram: 1 - Fan motor
2 and 3 - Connect directly to battery
This is a DC motor so polarity doesnot matter. If the fan operates reconnect it to the harness. If not, replace the fan.
thefan relay. You will need a multimeter to test. Remove the relay.
Switch on the ignition. Measure voltage at allthe connections in the
relay socket to earth. Two of them have to be at 12V or more. If not,
the problem is between thefuse and the relay. Re-insert the relay.
the thermoswitch. Usually located on the radiator. See photo : 1 -
Thermostatic switch. 2- Leaked and dried coolant on a neglected
the 2 wires from the harness that were a moment ago connected to the
thermo switch.(With a single wire thermo switch the wire needs to be
connected to earth or battery negative). Switch on the ignition. The fan
should start running again. If not switch off the ignition and remove
the relay again. You already know the connecting point with 12V. Measure
the other 3 wires for resistance to earth. One of themshould read more
than 5 ohm. Connect a lead between the "12V" connector and the "5ohm"
connector. Switch ignition on. If the fan runs the relay is faulty. If
not the wiring between the relay and fan is faulty.
Simplified wiring diagram:
B - Ignition Switch
C - Fuses
D - Relay
E - Thermostatic switch
F - Radiator fan
most obvious tell-tale would be a puddle of coolant under the vehicle
after a trip. Don't confuse this with condensation dripping from the
Inspect pipes for cracks and leaking at joints.
Inspect the radiator for dried coolant. (See photo above)
the engine block for coolant streaks. Leaks can start on the block
itself through the welch plugs which are also constantly exposed to
Another leak point is the water pump shaft seal which cannot be repaired. Replace the whole pump.
that the cabin heater is plumbed into the cooling system and can also
leak. Wet carpeting in the footwell is indicative of this although such
wet carpeting may also be the result of condensation from the A/C.How to wire a relay