Flushing the System
additives in antifreeze fight rust and corrosion breakdown and are ineffective after 1 to
2 years. This is because of the continual exposure to the heat in the cooling system.
After the additives break down, rust begins to form rapidly. Therefore, a rust-colored
antifreeze is an indication that the cooling-system service is required.
system should be cleaned periodically to remove rust, scale, grease, oil, and any acids
formed by exhaust-gas leakage into the coolant. Recommendations vary; for example,
Chevrolet recommends that the cooling system be drained and flushed every 2 years.
(cleaning) of a cooling system should be done based on the manufacturers
recommendations or when rust and other contaminants are found in the system. Flushing
involves running water or a cleaning chemical through the cooling system to wash out
contaminants. Rust is very harmful to the cooling system because it causes premature water
pump wear and can collect and clog the radiator or heater core tubes. There are three
methods of flushing-fast flushing, reverse flushing, and chemical flushing.
is a common method of cleaning a cooling system because the thermostat does not have to be
removed from the engine. A water hose is connected to a heated hose fitting. The radiator
cap is removed and the petcock is opened. When the water hose is ON and water flows
through the system, loose rust and scale are removed.
flushing of a radiator requires a special flushing gun device that is connected to the
radiator outlet tank by a piece of hose (fig. 6-14).
Another hose is attached to the inlet tank, so the water and debris can be directed to the
floor drains. Compressed air, under low pressure, is used to force water through the
radiator core backwards. The air pressure is used intermittently to loosen scale and
sediment. Excessive air pressure should be avoided to prevent damage to the radiator.
Starting and stopping the water flow produces a fluctuation in pressure and tends to
loosen all foreign matter clinging to the passages in the radiator core.
flushing can also be used on the engine block and head (fig. 6-15).
First, remove the thermostat and disconnect the upper radiator hose. Then disconnect the
lower radiator hose at the water pump. Insert the flushing equipment in the upper radiator
the system by sending water and air through the water jackets and coolant passages.
Following the flushing, replace the thermostat and hoses so the system can be refilled.
flushing equipment is not available, you can still reverse flush the system with a garden
hose. This is often effective following the use of a chemical cleaner.
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
Always follow manufacturers instructions when using a cooling system
cleaning agent. Wear protective gloves and goggles when handling cleaning agents.
Chemicals may cause eye and skin burns.