How to Flush a Radiator and Change the Coolant

Protect your engine from the elements in less than an hour

If you're driving a vehicle with an internal combustion engine, then periodically you'll need to flush the radiator and replace the coolant, which is also called antifreeze. 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. Fortunately, flushing your vehicle's radiator and changing the coolant is a snap. You can also use the coolant tester to determine the specific gravity of the coolant you already have and determine whether it's time for a flush and refill.

Vehicle System
Cooling System
Skill Level

This is a good project for new DIYers

Time to Complete
1 hour

    Prep: With the vehicle parked on a level surface, ensure the engine and radiator are cool to the touch. Antifreeze is toxic, so keep pets and kids from entering the work area. Also, have a container (to hold at least 2 gallons) ready to catch the used antifreeze, and wipe up any spills.

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

  2. Consult the vehicle owner’s manual for the location of the radiator petcock, or drain, and position the container on the ground under that drain, so it’s ready to capture 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. Run the engine for about 10 minutes until it reaches operating temperature. Then allow the engine and radiator to cool down, so that they’re cool to the touch.

  7. Repeat step 3.

  8. Pro Tip

    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, or leaking.

  9. Secure the used coolant in a closed container and take to your closest recycling center. There's likely to be quite a lot of used coolant and diluted coolant before you're done.

  10. Refill the radiator with pre-diluted coolant, ensuring it’s the type specified by your vehicle's manufacturer. (Use distilled water if you are diluting full strength coolant yourself. Aim for a 50/50 mixture).

  11. Pro Tip

    Using pre-diluted coolant, as opposed to concentrated or full-strength, is an easy, no-fuss way to ensure your radiator has the proper 50/50 mixture of coolant and water.

  12. Close the cap on the plastic reservoir, but leave the cap off the radiator and run the engine for 10 minutes with the vehicle heater on high. This helps remove any air pockets in the cooling system.

  13. Recheck the coolant level in the radiator and on the plastic tank where there should be a “full level” indicator. Add more coolant if needed.

  14. Close and tighten the radiator cap and reservoir cap.

  15. Pro Tip

    Just to be on the safe side, you may want to replace the radiator cap. They're cheap and they're a key part of the cooling system; a leaky radiator cap can be enough to cause all kinds of problems.

  16. For peace of mind, use an antifreeze tester to determine the lowest outside temperature to which your vehicle’s coolant is protected from freezing. Check out this video for details.

Last updated December 8, 2017