Chemical flushing is needed when a scale buildup
in the system is causing engine overheating. Add the
chemical cleaner to the coolant. Run the engine at fast
idle for about 20 minutes. Wait for the engine to cool.
Then drain out the coolant and cleaner solution. Using a
garden hose, flush out the loosened rust and scale.
Continue to flush until the water runs clear.
instructions when using a cooling system
cleaning agent. Wear protective gloves and
goggles when handling cleaning agents.
Chemicals may cause eye and skin burns.
Antifreeze should be checked and changed at
regular intervals. After prolonged use, antifreeze will
break down and become very corrosive. It can lose its
rust preventative properties and the cooling system can
fill rapidly with rust.
A visual inspection of the antifreeze will help
determine its condition. Rub your lingers inside the
radiator filler neck. Check for rust, oil (internal engine
leak), scale, or transmission fluid (leaking oil cooler).
Also check to find out how long the antifreeze has
been in service. If contaminated or too old, replace the
antifreeze. If badly rusted, you may need to flush the
Antifreeze should be changed when
contaminated or when 2 years old. Check the service
manual for exact change schedules.
Antifreeze strength is a measurement of the
concentration of antifreeze compared to water. It
determines the freeze-up protection of the solution.
There are two devices used to check antifreeze
strengththe antifreeze hydrometer and the
The antifreeze hydrometer is used to measure the
freezing point of the cooling system. A squeeze
and release bulb draws coolant into the tester,
and a needle floats to show the freeze protection
With the refractometer, you draw coolant into the
tester. Then place a few drops of coolant on the
measuring window (surface). Aim the tester at a
light and view through the tester sight. The scale
in the refractometer indicates the freeze
Minimum antifreeze strength should be several
degrees lower than the lowest possible temperature for
the climate of the area. For example, if the lowest
normal temperature for the area is 10oF, the antifreeze
should test to -20°F. A 50/50 mixture of antifreeze and
water is commonly used to provide protection for most
Vehicles, using an aluminum cooling
system and engine parts, can be corroded by
some types of antifreeze. Use only antifreeze
designed for aluminum components. Check
the vehicles service manual or antifreeze label
COOLING SYSTEM TESTS
It is often necessary to check the cooling system for
cooling system problems. Cooling system problems
can be grouped into three general categories:
1. COOLANT LEAKScrack or rupture,
allowing pressure cap action to push coolant out
of the system.
2. OVERHEATINGengine operating
temperature too high, warning light on,
temperature gauge shows hot, or coolant and
steam is blowing out the overflow.
3. OVERCOOLINGengine fails to reach full
operating temperature, engine performance
poor or sluggish.
To diagnose and repair cooling system problems,
perform several tests.
These tests include the
followingcooling system pressure test, combustion
leak test, thermostat test, engine fan test, and fan belt
Cooling System Pressure Test
A cooling system pressure test is used to locate
leaks quickly. Low air pressure is forced into the
system, causing coolant to pour or drip from any leak in
A pressure tester is a hand-operated air pump used
to pressurize the system for leak detection. Install the
pressure tester on the radiator filler neck. Then pump