How to flush a car’s cooling system

Check your car’s cooling system every 6 months. Flush the system and add antifreeze at least once a year. Antifreeze not only lowers the freezing point of the water in the system but also raises its boiling point; so it is needed in both winter and summer.

To check the system, remove the radiator cap and look inside. If the contents are very dirty, pour in a can of cooling-system cleaner; operate the car according to the can’s instructions. Flushing with water Flush the system with water after using the cleaner or if the system is only a little dirty. (If your car has no flushing T, get a flushing-T kit at an auto parts store and install the T following the kit instructions.)

Remove the flushing-T cap and attach a hose adapter. Then connect a garden hose. If the radiator tubes are vertical, remove the radiator cap and install the water-deflector nozzle in the cap neck. If the radiator tubes are horizontal, disconnect the upper radiator hose at the engine and aim the end away from the engine.

Start the engine, turn on the heater, and set the temperature to Hot. Turn on the water to the garden hose; fluid will pour out of the deflector or upper hose. When it runs clear for 2 minutes, shut off the heater, the engine, and then the water. Remove the deflector or reconnect the upper radiator hose.

Depending on your car’s setup, open the radiator petcock, or remove the drain plug, or disconnect the lower radiator hose. Let the water drain. Then tighten the petcock, or refit the drain plug or the hose.

Installing antifreeze – Install an amount of undiluted antifreeze equal to between 50 and 70 percent of the capacity of the cooling system (see your owner’s manual). The antifreeze will mix with the water remaining in the system (only the radiator has been drained).

Usually the radiator won’t hold all the antifreeze called for. In that case, see if there is an overflow reservoir connected by a hose to the radiator neck. If so, empty the reservoir and add the remaining antifreeze. If there is no reservoir, run the engine with the cap off the T, the heater on, and the temperature lever on Hot. As fluid dribbles out, add antifreeze to the radiator until the required amount is in. Then stop the engine, cap the T, and refit the radiator cap.

Caution: Antifreeze is poisonous. Keep it away from children and pets. Do not work with it when the engine is hot. Keep away from electric fans in the car unless they are disconnected.