Cooling systems can be your best friend when operating
efficiently. Cooling system repairs . . . your worst enemy if you don't
understand how your cooling system works.
Your cooling system performs a critical function. Simply
put, it maintains proper engine temperature by circulating coolant through the
engine to pick up heat and passing it through a radiator to cool it with air.
The coolant passes through a thermostat valve to control flow and possibly over
a temperature sensor which controls external air cooling fans.
Cooling systems consist of three main parts:
Cooling System Part #1: Pumping
Your cooling system's pumping function is handled by its
water pump, which keeps the coolant mixture moving.
The main water pump is gear- or belt-driven but, in many
cars, a secondary electric water pump is used for improved flow and cooling.
Critical to the pump's operation is the drive belt that
turns it. On most newer cars this is the engine's timing belt. On older cars,
the pump and belt are external and run off the main crankshaft pulley with a
"V" or flat belt.
Maintenance of cooling system pumping is limited to
scheduled coolant replacement and drive-belt replacement and tension adjustment
(external type). Timing-belt-driven pumps should always be replaced at the same
time as the timing belt and tensioner.
Cooling System Part #2: Piping
Your cooling system's piping consists of all hoses, any
control valves, the heater core, the radiator and the expansion tank. Because
of the materials used and the constant contact with coolant, all parts in this
system deteriorate more from time than use.
Maintenance of cooling system piping consists of scheduled
coolant replacement, replacement of all hoses on a regular basis and
replacement of any plugged or leaking parts.
All hoses should be checked at least twice a year for
abrasions, cracks, flexibility and evidence of leakage. Whenever the coolant is
drained for replacement or during engine repairs, any suspect hoses should be
replaced. All hoses should be replaced at least every few years.
Radiators, expansion tanks, heater cores and control valves
are normally only replaced due to leakage or plugging. The condition of these
parts should be assessed by a professional since proper functioning is critical
to many other systems within your car.
Cooling System Part #3: Temperature Control
Your cooling system's temperature controls include all
coolant temperature sensors, thermostat, radiator or expansion tank cap,
cooling fan(s) and fan clutch (if equipped). These cooling system parts
function primarily independent of the engine but control the engine either
through cooling or by sending control signals to your car's electronic systems.
The thermostat is a spring-loaded valve that opens and
closes based on the temperature of the coolant flowing through it. A high
temperature reading followed by a drop to normal temperature (or a continuously
low temperature) is a common first sign of a sticking thermostat. However, many
other conditions may cause these symptoms, so you need to know how to eliminate
each possibility.
The radiator or expansion tank cap is also a spring-loaded
valve reacting to system pressure. It serves to maintain proper system coolant
level at predetermined pressures. It must always be replaced with an exact
replacement cap with the same pressure setting. Never use other caps except for
short-term emergencies!
A belt-driven fan blade for pulling air through the radiator
is usually on the water pump pulley and should have a fan clutch to control it.
The fan clutch allows the fan to turn with the belt at low engine speed and
"free-wheel" at higher speeds. A bad fan clutch either doesn't allow
the fan to spin at low speed (overheating in traffic) or doesn't allow it to
free-wheel at high speed (potential overheating on highway or reduced gas
mileage).
An electric fan can be either by itself (usually front-wheel
drive) or auxiliary (used with a mechanical fan). Both types are controlled via
a temperature sensor - in the radiator or upper radiator hose or on the
thermostat or water pump housing. This sensor is usually an on/off type switch
with a fixed temperature setting. (Some vehicles may have 2-3 settings for
multi-speed fans.) This sensor is commonly called an "auxilliary fan
switch".
Other common temperature sensors are: 1) gauge sender
(variable output); 2) warning light sender (on/off type); 3) lambda and/or fuel
injection sensor(s) (variable to control fuel injection settings); 4)
thermo-time switch (cold start valve control). Your car may have other sensors
as well.
Temperature control is critical to both performance and
emission control. Unfortunately, this system is the most difficult to
troubleshoot without proper equipment and diagrams. It's even more difficult
with computers that adjust timing, idle speed, vacuum and fuel delivery
automatically to make up for potentially faulty temperature sensor signals.
Maintenance of your cooling system sensors is virtually
impossible since there's nothing really to "maintain". Keeping them
clean both internally (coolant replacement) and externally (engine cleaning) is
the best way to ensure trouble-free driving. Checking and replacing all parts
at the factory-recommended time or mileage limits helps as well.
A Few Important Things to Remember
Heed these cooling system maintenance tips and you're well
on your way to ensuring your cooling system won't let you down:
Tip #1: Keep your engine and engine compartment, as
well as your radiator fins and grill, as clean as possible. A clean engine runs
much cooler - and it's much easier to work on.
Tip #2: Replace coolant at or before factory
recommended intervals with the proper type, mixture and volume of coolant.
Always allow the coolant system to rid itself of air before installing the
radiator cap.
Tip #3: Replace all cooling system hoses - upper and
lower radiator hoses, bypass hoses, heater hoses, manifold coolant hoses and
any other hoses on your vehicle - whenever you even suspect there may be a
problem. All hoses should be replaced at least every two years.
Tip #4: Replace the thermostat with the original
temperature setting equivalent. The electronics in your vehicle may use that
setting for other controls. Do not substitute under any circumstances.
Tip #5: Replace the radiator/expansion tank cap with
the original pressure setting and OE-type equivalent. Some aftermarket
substitutions do not seal and hold pressure properly on foreign-manufactured
cars. Again, don't substitute.
Tip #6: Adjust or replace the water pump drive belt
(external) at recommended intervals or more frequently, if required. Check
belts whenever you're working on any coolant system components.
Tip #7: Replace your water pump with an OEM/OES pump at
the first signs of trouble or when your timing belt and tensioner are replaced.
Watch for signs of overheating - you don't want to break down in the hot sun
when your water pump fails.
Tip #8: Replace the fan clutch and/or fan blade as
needed (if applicable). Your car's temperature gauge is often your best guide
as to when your fan clutch needs attention.
Tip #9: Replace temperature sensors as required by
diagnosis. Leave troubleshooting of your sensors to experts who have the proper
equipment and diagrams.
Tip #10: Keep your entire vehicle properly maintained
because of the effect timing, idle speed, exhaust and other systems have on
your engine's temperature. Your car's cooling system is designed to function
with all other systems operating properly. It cannot make up for a poorly
operating or overheating engine condition.
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