How To Drain A Cooling System

How To Drain and Refill a Sealed Cooling System?

A car’s cooling system is responsible for the effective working of the car’s engine. The coolant inside the system helps to lower the high temperatures produced. Regular draining and refilling a fully sealed cooling system can help ensure that your car’s engine operates at an optimum condition and the cooling system itself doesn’t wear out easily.

The following steps can guide you and provide you a solution on how to drain and refill a fully seated cooling system without any additional assistance.

Safety Concern

The coolant inside the system can reach very high temperatures. Please ensure that the engine is cool before working on the cooling system to avoid any serious injuries or damages.

Draining out the coolant

Step 1 – To drain out the old coolant from the car, you will require a draining pan.

Step 2 – To start the draining process, you will first need to press down the radiator cap and turn it counter-clockwise very slowly until you start hearing the hissing sound. Once the hissing sound stops, only then remove the radiator cap.

Step 3 – Now place the draining pan underneath the car’s coolant draining valve, which is present at the bottom of the radiator. Slowly loosen the valve to let the coolant drain out.

Note: If the car doesn’t seem to have a draining valve, you can also unclamp the lower hose of the radiator and pour the coolant into the draining pan from there. But make sure you don’t damage the hose pipe in the clamping process.

Environmental hazard

The used coolant for the car can be extremely toxic for the animals and the environment. Soak up any spilled coolant with paper towels or rags. Make sure you responsibly dispose of the coolant to avoid causing any damage to the environment or biodiversity.

Flushing the cooling system

To remove any remaining debris from the system, you can use a radiator flush to thoroughly clean the cooling system before refilling it with a new coolant. Follow the following steps to flush your car’s cooling system.

  • Close the draining valve.
  • Pour the flush into the system from where you removed the radiator cap.
  • Place the radiator cap back on.
  • Turn on the ignition for 5 minutes to let the flush run through the whole system.
  • Let the engine cool down for 15 minutes before proceeding to loosen the radiator cap slowly.
  • Only remove the cap once the hissing sound stops.
  • Place another draining pan underneath the draining valve.
  • Open the draining valve to let the liquid pour out.
  • You can continue to repeat the flushing process until the outflow from the system appears to be clear in the draining pan.
  • Dispose of the unclean flush liquid responsibly as it may also be bad for the environment.

Checking for any additional damages

Before refilling the cooling system with a new coolant, you must ensure that all the cooling system components work properly to avoid any spillage or wastage. In particular, the hoses and the radiator cap are prone to most damage over time. If they are damaged, you should replace them immediately. If there are any visible leaks in the hoses, you can use a radiator stop leak to seal the damaged area for the time being.

Refilling the Cooling system

Step 1 – The first step of refilling the cooling system is choosing the right coolant that has been specified for your car.

Step 2 – Make sure you read the instructions on the bottle and find the accurate amount of dilution needed for the coolant mixture. The dilution must be done with distilled water, as tap water can cause mineral deposits to form around the neck of the radiator. Add the required amount of coolant and distilled water in a clean bucket. Mix the two thoroughly.

Step 3 – If the draining valve is open from the draining process, you need to close it.

Step 4 – You then need to jack up your car to reduce the possibility of air pockets forming in the engine as you pour the coolant mixture into the radiator. Air pockets can be very detrimental to your car. They may lead to overheating the engine by reducing the circulation of the coolant in the system and can also accelerate the rusting of the system.

Step 5 – You will require a funnel to avoid any spillages of the coolant mixture. You can fill the coolant either through the radiator or the coolant overflow tank. If you fill through the radiator, make sure you stop pouring in the mixture 1 inch below the neck of the radiator and a couple of inches below the mentioned mark if filling in through the overflow tank.

Step 6 – Start the engine and let the mixture run through the system. As the engine heats, the coolant level drops, implying that the thermostat has opened up. It is then time to add more coolant mixture. This time bring the mixture to the top level of the radiator or the ‘HOT’ mark indicated on the coolant tank.

Step 7 – Shut the engine off and put the radiator cap back on.

Step 8 – Remove the jack from the car, and you can now take your car for a ride.


If air gets trapped in the system, you must immediately get it out. Some cars have a bleeding valve on the upper radiator hose to let the trapped air out. If the valve is not present, the overflow tank must be dismounted and pulled upwards so that the trapped air can vent out. You can check out this guide if your brake fluid is not coming out while bleeding.

There you have it step by step guide for draining and refilling a fully sealed cooling system. A functioning cooling system is essential for the smooth running of your car. Routinely change of the coolant can prolong your car’s engine life exponentially. The whole process can take around half an hour to an hour but can save you unnecessary trips to the mechanics.

Note: If the car continues to overheat after coolant change, you should check if the engine oil needs a change. Also see if the radiator fan working properly. Replace the radiator fan and change the steering fluid if it seems faulty.


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