How to flush a radiator and to change the coolant

Protect your engine from the elements with a radiator flush.

After driving 40,000 to 60,000 mi (64,000 to 97,000 km), it’s recommended to change the coolant in your radiator to keep your engine running well. Especially if you are driving with an internal combustion engine. Changing the coolant requires draining the existing fluids and flushing the system before you add a new antifreeze solution. Adding fresh radiator coolant with the proper 50/50 mix of coolant and distilled water protects your radiator from overheating in summer and freezing in winter.

Flushing a radiator and changing the coolant is very easy. Sometimes you can use the coolant tester to determine the specific gravity of the coolant you already have. Then you can decide whether or not it's time for a flush and refill.

What you will need:

Before you begin, park your vehicle and let the engine cool down so you can touch the radiator. As antifreeze is toxic, keep the kids and pets away from the working place. Also, prepare a container for the used antifreeze.

1. Open the radiator fill cap which is located on top of the radiator. If your vehicle has a plastic tank or reservoir for coolant, open that cap too.

2. Use the vehicle owner’s manual to ensure the location of the radiator petcock, or drain. Then position a container on the ground under that drain so it is ready to catch the escaping antifreeze.

3. Open the drain, and allow all the coolant to drain into the container until it stops flowing out. Then close the radiator petcock or drain.

4. Pour the radiator flush product into the radiator. Fill the radiator with water from your garden hose until it’s about one inch below the radiator neck. Follow the product directions.

5. Close the radiator and reservoir caps.

6. Turn on your vehicle for about 10 minutes with the heater on high after it reaches operating temperature. Then let the engine and radiator to cool down until you can touch them.

7. After draining the radiator, close the petcock or drain. Refill the system with water and replace the caps. Turn on your vehicle again for about 10 minutes with the heater on high after it reaches operating temperature. Let the engine to cool down.

8. Remove the caps and repeat step 3.


While your radiator is drained, take the opportunity to inspect the upper and lower radiator hoses. Replace the hoses if they're cracked, brittle, bulging, leaking or old.

9. Keep the used coolant in a closed container and take it to your closest recycling center.

10. Pour the specified type of pre-diluted coolant into the radiator. Use distilled water if you are diluting full strength coolant yourself. Aim for a 50/50 mixture for most climates.

11. Run the engine until the cooling system stops bubbling and the coolant level starts to rise, then put the radiator cap back on the system. If your vehicle is equipped with a coolant bleed screw, use this instead of the radiator cap method.

12. Check the coolant level in the radiator and on the plastic tank. It should be until the “full level” indicator. Add more coolant if necessary.

13. Close the radiator and reservoir caps properly. It is also recommended to check the coolant level after one to two days.


Sometimes you will need to replace the radiator cap. They're cheap, and they're a vital part of the cooling system; a leaky radiator cap can cause quite a few problems.

14. Use an antifreeze tester to determine the lowest outside temperature to which your vehicle’s coolant is protected from freezing.