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How to Flush a Radiator with a Garden Hose

How to Flush a Radiator with a Garden Hose

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Why Does a Radiator Need to be Flushed?

As with anything metal, over time rust and other deposits tend to build up within the radiator. It is always recommended to reference the vehicle’s owners manual but a common guide is every 50,000 miles it should be flushed as a standard maintenance precaution.

In flushing and cleaning a radiator with a garden hose it will allow all the rust and other deposits that have built up to be flushed out keeping the radiator running clean.

What is Needed to Flush a Radiator with a Garden Hose?

  • Gloves (optional but recommended)
  • Drain Pan (5 Gallons or more should do the trick)
  • New Antifreeze
  • Water Source
  • Garden Hose
  • Distilled Water for Refilling (unless new antifreeze is pre-mixed)
  • Radiator Flush Product such as Prestone’s Flush & Cleaner
  • Antifreeze tester

How to Flush a Radiator with a Garden Hose?

Always wait for the engine to become cool to the touch. If the cap is removed while the radiator is still hot the fluid can shoot out and burn you.

Start out by finding your radiators reservoir tank. It will most likely be a white plastic tank with a plastic cap.

Next, locate the drain valve which should be located on the bottom of the radiator. If it can’t be found either check your user manual or simply google your make, model and year to find it.

Prior to opening the drain make sure you put your drain pan under it. Once complete simply open the drain and let the antifreeze drain completely.

When no more fluid is draining out, simply close the drain valve back up.

How to Refill a Radiator with a Garden Hose?

Always follow the Flush / Cleaner directions but you should be able to just pour the contents of the Flush / Cleaner into the reservoir or directly into the radiator at this time.

Once complete take your garden hose and fill the radiator up to the full mark on the reservoir or radiator. Prior to starting the car, ensure both the radiator and the reservoir caps are back on. Start the car and wait for the engine to get up to normal operating temperatures (usually about 5 minutes).

Turn the heat on full blast in the car. Let the car run another 10 minutes to really let the radiator get flushed and cleaned. After 10 minutes simply turn the car off and let it sit until it is cooled down.

Once cooled back down open the radiator or reservoir back up. Put the drain bucket back under the radiator and open the drain up so everything drains again.

Repeat the previous process but instead of using the flush and cleaner just take the garden hose and fill it with just water. Don’t forget to close the radiator and reservoir and then start the car back up and let it run for another 10 minutes.

Let the engine cool again. Once cool, place the pan under the drain and drain the water out.

This time refill the radiator with the new antifreeze / engine coolant. In doing so make sure you don’t forget to test the antifreeze to verify it has enough antifreeze to for when winter hits, especially if you live in colder climates like Michigan or further north.

If you purchased straight antifreeze you will want to fill your reservoir with 50% antifreeze and 50% distilled water. The distilled water wont have any iron in it like a garden hose so it is best to use distilled to prevent faster build up again.

Antifreeze is also available prematurely mixed should you not want to hassle with mixing them. Just make sure the bottle says 50% antifreeze and 50% water or it will say pre-mixed.

If you aren’t comfortable in doing this yourself you can get it done at most oil changing places. It will probably cost about $125 to have this done.

How to Test the Antifreeze in a Radiator?

How to Test the Antifreeze in a Radiator?

In order to do this an Antifreeze/Coolant Tester will be needed. These testers provide a quick and easy method to safely sample and measure the engine coolant. They will help prevent freezing in the winter and overheating in the summer.

Make sure your car has ran some prior to testing to confirm everything has been mixed up well (this is only if you have just replaced the antifreeze with 50% antifreeze 50% distilled water).

However, in doing so don’t let the engine get to hot as the antifreeze will expand creating a pressure at the cap. Make sure the car is off.

How to Test the Antifreeze in a Radiator?

Start out by locating the antifreeze reservoir.

How to Test the Antifreeze in a Radiator?

Remove the reservoir cap slowly if the engine isn’t fully cool in which you will most likely hear a hissing sound. This is just the reservoir releasing the pressure that has built up.

How to Test the Antifreeze in a Radiator?

Insert the tester into the engine coolant reservoir.

How to Test the Antifreeze in a Radiator?

Squeeze the ball at the top which will such in the antifreeze. Get enough to fill the tester.

How to Test the Antifreeze in a Radiator?

Hold the tester up keeping it level and see where the needle falls. If you are in the cold climate you will want to see what the blue reads out. This is the temperature the antifreeze can withstand before it starts freezing.

In this particular vehicle it is ready to go in temperatures as cold as -35 degrees.

How to Test the Antifreeze in a Radiator?

When you are done getting the reading simply return the antifreeze to the reservoir and put the cap back on.

How to Test the Antifreeze in a Radiator?

It is also important to rinse the antifreeze tester out. If you don’t the needles will get gummed up and not work properly in the future.

To clean the antifreeze tester simply fill it with hose water and squirt it out a couple times. It is as easy as that.

How to Properly Dispose of Old Antifreeze (Coolant)?

Antifreeze is considered a hazardous liquid so it should be disposed of properly. A lot of auto part places will take automotive fluids and recycle them. If you aren’t sure where to dispose of these liquids simply use Earth 911.

This site has a free recycling locator. Simply put in your zip code and select the liquid you are trying to discard and Earth 911 will find your closest locations for you.

What is the Function of the Radiator?

The function of the radiator is to assist in either heating or cooling something. In a vehicle the fluid is ran through the motor which picks up heat and brings it back to the radiator.

A combination of the fan blowing on the radiator while sitting still or the wind hitting it while driving will cool the fluid. As this process completes the fluid is continuously flowing through the motor repeating.

The fluid is driven by a water pump. This water pump is connected directly to your motor and the hoses assist with completing the circulation from point A to point B.

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Sunday 4th of October 2020

I really like your article, great extra information. My car manual says to take out the thermostat plug too, which I did not see in your article.


Tuesday 6th of October 2020

Hi Jonathan,

Cars are constantly evolving in which I would recommend following the owners manual to error on the side of caution. Good luck!