Lesson 5/Learning Event 2
Sometimes it is recommended that the cooling system be flushed out twice a year--once in the fall when
antifreeze is added and again in the spring when antifreeze is drained. Other times flushing may only be done
when the coolant is contaminated. At any rate, regular flushing by organizational repairers will reduce clogging
and overheating so that corrective cleaning by higher maintenance will not be needed very often. However,
anytime the cooling system is clogged enough so that it causes the engine to overheat, turn the vehicle in to
higher maintenance for repairs.
To do a good job, you should use a cleaning compound before flushing the cooling system. The cleaner is a
very strong acid that will loosen rust, scale, and sludge. The acid will damage cooling system parts if it is
allowed to stay in the system, so its use must always be followed by a neutralizer to stop the action of the
cleaner. The cleaner and the neutralizer normally come packed in separate compartments of the same
container. Always read and use the instructions printed on the cleaner container and in the -20 technical
manual for the vehicle you are working on.
With the drain cocks closed and the engine temperature below 200F, fill the cooling system with clean, fresh
water. Install the radiator cap and run the engine for about five minutes after it has reached normal operating
temperature. Stop the engine and drain the cooling system. If the water is discolored to any extent, repeat this
flushing process until it drains clear.
Always flush the cooling system by the pressure flushing method if a flushing gun is on hand. The pressure
method is more effective than normal flushing for removing loosened rust and scale. Pressure flushing is done
through the system in a direction opposite to the normal coolant flow. This allows the flushing pressure to get
behind the deposits, forcing them out.