How to Flush a Radiator With a Garden Hose? – 8 Steps

how to flush a radiator with a garden hose

A radiator plays an essential role in keeping the temperature of our car at a safe level. The condition of your radiator will affect the car’s engine and the air conditioning system, so it is best to take care of it.

Depending on the state of your radiator, a radiator flush will cost you around $50-$150. Car owners want to save money and do this procedure on their own. I will give you a detailed and helpful guide on how to flush a radiator with a garden hose.

Step-by-Step Guide

What to prepare:

  • Garden hose
  • Basin
  • Engine cleaner solution
  • Water source
  • Coolant
  • Distilled water
  • Pliers
  • Mechanic gloves (optional)
  • Funnel
  • Duct tape
  • Socket wrench

First of all, make sure you read the car’s manual to know where the specific parts are located.

Step 1: Drain the used coolant.

flush engine block garden hose

Before draining a radiator system, make sure that your car engine is turned off, and that the radiator is safe to touch. Put on your mechanic gloves to start working.

Once the temperature is cool enough, place your basin below the drain plug and open it to remove the used coolant.

Throw away the used coolant on the drainage system properly, as it can harm the environment and animals if you just pour it anywhere.

Step 2: Pour the cleaning mixture into the radiator hole and then drain it.


You can use any engine cleaner and dilute it with water using a 1:3 ratio. Use a funnel and pour the mixture into the radiator hole that can be seen on top of the radiator.

Turn on the engine to let the cleaning mixture flow through the passages of the radiator and engine block. Let it go on for 10-15 minutes, as the thermostat needs a higher temperature for the mixture to circulate.

Your engine must be cooled down before you drain the cleaning mixture. Once safe to touch, open your drain plug once again to remove the cleaning solution.

Step 3: Check the thermostat


Before you flush a radiator system with water at home, take some time to check your car’s thermostat.

You can still flush a coolant system even without removing the thermostat; however, I recommend you do this step to know if your thermostat is still working and also to clean it.

To remove the thermostat:

  1. Follow the lower engine hose of your radiator to locate the thermostat housing.
  2. Cover the alternator below it to avoid making it wet.
  3. Use a socket wrench to remove the bolts off the thermostat housing, and then use a plier to loosen the lower hose clamp.

Remember the position of the thermostat so that you can place it back quickly once you’re done cleaning or checking it. Now, you can start to flush out a radiator coolant.

Step 4: Flush water through the passages of the engine block and radiator to rinse the cleaning mixture.


Without a radiator backflush kit, you can make a homemade radiator flush at home with a water hose or a garden hose.

Without a water hose, you can also use a funnel to pour the water into the passages manually. This method will be hard since pressure is needed to flush a central heating radiator.

The best way to flush a radiator and engine block is to perform this step for these parts separately.

  1. Detach the lower and upper hose from the radiator by loosening the clamps using a plier. Now, both parts have two ends.
  2. Flush the cooling system with a garden hose from the side hole of the radiator and let the water flow to the lower engine hose, then vice versa. Suppose you noticed that the water is not flowing well. You need to use a high-pressure head to attach to the end of your garden hose to flush a clogged radiator.
  3. Flush the engine block with a garden hose using the same method you used for the cooling system or the radiator. Let the water flow until the water that is coming out is clear and has no more debris.

Read more: Detailed Guide on Cleaning a Clogged Radiator.

Step 5: Pour distilled water into your cooling system and then drain.

Tap water is likely to bring rust and impurities to your cooling system.

  1. To ensure no such thing will happen, pour distilled water into your radiator. Make sure that the engine hoses, drain plug, and thermostat are back in their places.
  2. Turn on the engine to increase the temperature and let the distilled water circulate through the system with the thermostat’s function for 5-10 minutes.
  3. After that, let the car and its parts cool down before draining the distilled water.
  4. Once cooled down, open your drain plug and let the distilled water come out.

Step 6: Add coolant.

After you properly flush a radiator, you now add your coolant. You can use a pre-diluted coolant or mix the coolant on your own.

A ratio of 1:1 of coolant and distilled water is recommended to fill the capacity of your cooling system.

Check your car’s manual for the coolant capacity or other instructions that are specific to your car.

Step 7: Turn on the engine to remove the air from the cooling system.

Burping your radiator is a must after pouring your coolant.

You may notice that your radiator is full even though you haven’t consumed your car’s recommended coolant capacity. That is because of some air that is trapped in your cooling system.

  1. Place a funnel on the top hole of your radiator, and make sure to fix it with duct tape, so it stays in place and does not spill.
  2. Turn on the car’s engine, so the thermostat will let the coolant circulate through the engine block and radiator.
  3. Slowly pour the coolant into the radiator until it can be seen until the one-forths of the funnel. If the coolant is not going down anymore, try to squeeze the upper engine hose to push more air out. If, after more squeezes and the coolant is not going down anymore, that means your cooling system is now full.
  4. Remove the funnel and duct tape, and close the top hole of your radiator with its cover.

Step 8: Test Drive


Lastly, go for a test drive for 10-20 minutes. Make sure that you check your car’s temperature while driving safely. If the temperature keeps going down, there’s still air in your cooling system, and you need to repeat step 7.

On the other hand, if the temperature is constant throughout your test drive, then you successfully flush a cooling system with a hose on your own.

The Importance and Benefits of Flushing the Cooling System


Flushing your coolant system is beneficial and even very important to your vehicle. It removes all the rust and deposits that risk damaging your car radiator, thus avoiding overheating.

Furthermore, it will protect from further built-up scale deposits and corrosion.



What is radiator flushing?

A radiator or coolant flush is a procedure that removes your old coolant and replaces it with a new coolant to avoid engine overheating. This procedure also checks if the radiator and engine block are rusting, and to check if there are leaks from the engine hose.

How to know if a radiator needs to be flushed?

Major signs that your car needs a radiator flush;

  • Your car is overheating.
  • Your coolant is leaking. You will smell maple syrup if your coolant is burning.
  • Your car needs maintenance. It is recommended to have your radiator flushed every 50,000 to 70,000 miles, depending on your car’s model, check the manual to know the specific number.

How often should you flush your radiators?

Once every five years or every 50,000 to 70,000 miles, you need to flush your cooling system. However, if the signs that your car needs a radiator flush are showing, you need to have it for the safety of your car.

How to know if your thermostat is working?

In relation to step 3, to check if your thermostat is still functional, you need to submerge the thermostat in hot or boiling water. It works if the displacement needle or pin goes down along with the charge cylinder. Once you remove the thermostat from the hot water, the displacement needle should rise back to its normal position.


Following these 8 steps on how to flush a radiator with a garden hose needs a lot of work and patience. However, you need to do it only once every 5 years. If you can do it yourself, why not do it on your own, right?

After learning this, you can even flush the radiators of other people’s cars. I hope this guide helped you a lot, and that you’ve learned to do the steps on your own. You can also share this article with your family and friends to help them too. Thank you for reading!

Related: Cleaning Radiator Fins – 5 Detailed Steps.

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