How To Flush Cooling System

How To Flush Cooling System

Preventative maintenance can eliminate most problems caused by cooling system failures. But what kind of maintenance? Your car’s cooling system is made up of many components, including the radiator, water hoses, water pump, thermostat, heater core, and many others. These parts need to be periodically replaced based on their service life and the recommendations of your car’s handling manual. Here we are going to talk about the liquid (coolant) that runs throughout the cooling system. This liquid is responsible for moving heat away from the engine and is named antifreeze.

Let's talk about the nature of the liquid cooled engine first. During the normal operation of the engine, huge amounts of heat is generated, which is generated by explosions within the cylinders. If this heat is left to go unchecked, the engine would be overheat and cease to function because the oil and other engine components would fail and that's just the beginning of problems. Liquid is very good at dissipating heat, so this liquid is pumped throughout the nooks and crannies of the engine, thus removing the heat and taking it to an area where it can be cooled down. This area is the radiator and it is located at front of the car. The radiator allows the heat to dissipate quickly, and once cooled, the liquid is then pumped back into the engine where the cycle repeats. This cooling process can actually be performed with plain water, however plain water has two characteristics that aren't conducive to the operation inside an engine. First, water is not good at rust and corrosion prevention. Second, water freezes at an unacceptable temperature for normal vehicle operation. So water is better than ice.

As a result, we add antifreeze to the water to give it the desirable characteristics for operation within an engine. Most antifreeze is made from ethylene glycol and is colored green, yellow, red, orange, pink, or blue. Because of the ethylene glycol, antifreeze prevents corrosion in the cooling system and freezes at a much lower temperature than water, almost making it the perfect substance for cooling an engine. But the problem of antifreeze is that it cannot work forever. Typically, it looses its protective properties after just two years or 30,000 miles. There is extended-life antifreeze available that can work longer, but that is just exception, not the rule.

And then it comes to flushing your cooling system.


Make sure that your engine is cold. If you have been driving the car, let it cool for at least an hour before attempting to drain the system. The first thing you need to do is get rid of the old coolant. Remove the radiator cap so that you can let air into the system. You may have to raise the front of the vehicle to get to the bottom of the radiator. This is a messy job, so make sure you have plenty of rags and paper towels at hand. Also, wear goggles or safety glasses to protect your eyes as coolant burns.

Make sure that you have a drain pan with a large enough capacity to catch the coolant, and you can find the total engine coolant capacity in your owners or service manual. Move the dashboard ventilation lever to HOT to open the valve to the heater core. Then open the plug and watch the show. If you don't have a drain plug, just disconnect the lower radiator hose at the radiator. Removing the coolant from the radiator will evacuate about 45% of the coolant from the system. If your engine has a water drain plug on the engine block, removing it will help clear the antifreeze from the system faster than by just draining the radiator alone.

After the first draining, close the bottom of the radiator, fill the system with water, briefly run the engine, drain and repeat, thus "flushing" the system. Please make sure that the final system draining reveals clear water and no more antifreeze. If your city doesn't have hazardous waste disposal for the spent antifreeze, the safest way to get rid of it is to pour it into a household drain, clothes washer pipe, or toilet. Don't pour it onto the ground or into a storm drain. Make sure you keep the old and new antifreeze away from animals and children as it’s poisonous.

cooling system

Filling and Bleeding

Now that the system is clear of the old antifreeze, you need to fill the system with the new antifreeze. Again, check the total capacity of the system. Fill the system with half antifreeze and half water. Some antifreeze in the market is pre-mixed 50/50 with water, so if this is what you have, just fill as-is. The engine block has lots of nooks and crannies, so you need to take care when removing trapped air. The radiator fill cap and neck should be at the high point of the system to allow air to bleed out, however sometimes this is not the case. So if you have not raised the front of the vehicle, it’s the time to do so.

Fill the radiator with the antifreeze or antifreeze/water mixture. You may have a bleed screw somewhere on the top of the engine. If so, open it to allow air to escape. Slowly pour in the required amount of antifreeze until you see it oozing from the air bleeds and then close the bleed screws. Pour the remaining antifreeze into the radiator and top off the system with water.

If your system has a heater core valve, move the dashboard switch to COLD to close the system. Now with the engine running and warm, have someone move the dashboard switch back to HOT and listen to the valve. You should hear an initial rush of coolant into the heater core. After that, the valve should be silent. If you hear the gurgling sound of bubbles, air is still in the system. Check the whole system for leaks and then lower the vehicle. Make sure that you periodically check the coolant level in the system over the next few weeks. Continually top off the radiator as necessary as air rises to the top.

Removing old coolant and adding new coolant isn't too much difficult. It just takes time and a little patience. Doing this at the proper intervals will aid in the protection of your cooling system components.

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