How to Flush a Radiator with a Garden Hose

Local environments can affect the performance of a car, and none more so than keeping the engine cool so that it won’t overheat.

While there are many things, you need to take your vehicle to the garage to have done. You can do some things at home with some very basic auto parts to help extend your vehicle’s life and save some money.

Because the cooling system is so critical to the performance of a vehicle, your vehicle can benefit from flushing radiator cars, trucks, or other vehicles, which uses conventional combustion engines.

Flushing a Radiator with a Garden Hose

It may sound hard to clear out the entire gunk from your radiator, yet in practice, with a good quality garden hose, the job doesn’t take long, and the steps are easy to follow.

Here, we look at how to flush the cooling system with a garden hose.

Why Do I Have to Flush My Cooling System?

Modern vehicle engines are full of aluminum, from cylinder heads, water pumps, engine block, and more.

Two other key components, such as the radiator and heater, are also made of aluminum. Although aluminum does not rust, it can suffer corrosion by being submerged underwater for prolonged periods. To last, it needs great corrosion protection to ensure its survival.

When periodically flushing the radiator and replacing the coolant (antifreeze), you should add the coolant from the radiator in the correct 50/50 ratio of coolant and distilled water. This helps prevent radiator overheating in summer and freezing in winter.

Over time, this sediment begins to block the water channels in the radiator and engine. Once these blockages reach a certain level, they lead to overheating.

If this happens at severe levels, it can lead to the engine shutting down and failing.

Corrosion inhibitors (antifreeze) come in green, red, and orange. Red and green provide about two years of use, while orange offers a little more time.

However, if your car already has green or red, then you can’t just add orange without flushing the system first. (Read What to Do When Lawn Mower Won’t Stay Running)

Things You’ll Need

  • Recommended coolant or antifreeze for your vehicle
  • Drain buckets
  • Garden hose with a good flow of water
  • Radiator flushing products
  • Gloves and goggles
  • Antifreeze level tester
  • Old rags
  • Sharp utility knife

Once you have the above, make sure you park your vehicle on a level surface. Both the engine and your radiator need to be cool to the touch.

Make sure there are no pets or children around as these vehicle coolants are toxic.

Flushing Vehicle Cooling Systems

When you are looking to flush the radiator, you can see there are two ways you can do this.

One is the regular way, and the other backflushing radiator to remove built-up grime that settles in small parts of the cooling system.

Here, we will show the two ways you can flush a radiator to keep your car running cool or without freezing in the cold.

Radiator Flush and Coolant Change

Here are the easy to follow steps for regular coolant system flushing.

  1. Open the radiator-filling cap that is located on the top of the radiator. If your vehicle has an expansion tank, open the cap on that also.
  2. Check to find where the radiator drain valve or petcock is located. Position your drain bucket underneath so you can catch the waste coolant.
  3. Open the drain plug and let all the liquid run into the bucket to drain the radiator. Once empty, close the drain or petcock.
  4. In the top radiator cap, add the radiator flush treatment. After you add this, use your best garden hose to fill the radiator until it is one inch below the neck of your radiator. Make sure you check the instructions on the flushing chemical bottle.
  5. Close both your rad cap and the cap of the pressure cap on the expansion tank.
  6. Start the engine and run until it is at running a temperature. With your heater control, turn your heater on full blast. Running the heater on high, causes the thermostat to open and lets the water and flushing liquid flow around the system. Some motorists also remove the thermostat to achieve the same thing. Leave it in place, and it gets a clean.
  7. After ten minutes of running, turn off the engine and let your vehicle stand until it is cool to the touch.
  8. Open the radiator drain plug and pressure caps, and catch the flushing water into your bucket. If no water drains, use a piece of wire to poke because you may have sediment buildup.
  9. Remove both the top and bottom radiator hose by loosening the hose clips.
  10. Take your garden hose and place it in the top hole of your car radiator. Use the rags to make a good seal.
  11. Flush the radiator with tap water until all the dirt comes out, and the water runs clear.
  12. Close the drain vale and top up with pre-diluted coolant. You can use distilled or regular water to make up the 50/50 concentration. Distilled doesn’t contain salts that make up the sediment.
  13. Run the engine until the coolant no longer bubbles and the level begins to rise. Replace your radiator screw-on cap.
  14. Top up the expansion tank if the level is not by the maximum level.

Back Flushing Your Coolant System

The first method does an excellent job of cleaning and draining the radiator, yet you may need to backflush the entire system.

This will dislodge any stubborn sediment from inside the engine cooling channels of the block and thermostat housing.

To make this easier, you can purchase backflush kits that are suitable for most makes of vehicles and trucks. Aside from this, you need a good radiator cleaner and the items listed before the regular method.

Here are the straightforward instructions to backflush your system:

Make sure you are close to a drain or have your drain buckets handy.

The engine should be cool and de-pressurized by removing the upper radiator cap.

Cut through the heater inlet hose with the utility knife at the straightest point. This runs from the heater core by the firewall to the top of your engine. Add a hose clamp from the kit to each cut side.

Add the correct sized T-fitting (various sizes come with the kit) and fasten the hose clamps with a screwdriver.

Best Garden Hose

Connect the black end of the backflow prevention coupler onto your T-fitting. Take your best water hoses and connect onto the yellow end of the coupling. Be sure your garden hose is away from moving parts.

Connect the splash tube. You can also add another plastic tube as this allows better drainage away from your vehicle.

Use your drain bucket or open-drain for the wastewater.

Open the drain plug that is located at the lowest point.

Turn on the faucet and check there is water coming to the splash tube.

Start your engine and turn the heater to full. Let your vehicle idle as the water pump pushes water through the complete engine system.

Water will eventually run clear after the vehicle has been running for around 10 minutes.

Once you see clear water, you can turn off the engine and remove the garden hose, the splash tube, and the backflow prevention coupler from the T-fitting.

Be sure to open the drain valve and let all the water run from the system. When empty, you can close the drain valve and the T-fitting on the flushing fitting with the included cap.

You can now change the coolant with your premix of 50/50. Be sure the coolant level of the new antifreeze mix is by the maximum level in the expansion chamber.

Radiator Maintenance and Cleaning

More Radiator Cleaning

Once you change the coolant, you need to check there are no leaks from your backflush parts, the bottom, or the upper radiator hose.

You will need to keep an eye on the levels over the next couple of weeks to make sure they stay at the right levels.

While doing these coolant changes, some vehicle owners clean their radiators on the outside.

To do this, you have to remove your radiator from the vehicle and connect your garden hose to the best pressure washer that is ideal for these jobs around the home.

With your pressure washer, you can fire the water through the aluminium fins to clear dead flies, insects, and any dust accumulation. All these can affect the cooling capacity of your radiator.

From start to finish, you can clean the entire system in your vehicle, and add new coolant. The entire process takes three hours maximum.

You can save quite a bit of money by doing it yourself, and you have the advantage of knowing it is done right.

How to Flush a Radiator with a Garden Hose

3 thoughts on “How to Flush a Radiator with a Garden Hose”

  1. Couldn’t you just feed the garden hose into the top hose of the engine with heater valve open and disconnect the bottom hose to flush out the engine? Seems the water pressure of the hose would do the job without running the engine. Just remove the thermostat first to open the path.

    1. yes that works too. just did it on my 2000 mustang v6. I was changing the timing cover because of oil leaks around main seal, and ran the garden hose through the neck and flushed it that way. the water in the upper neck will push all the old nasty crap out of the pump and into a bucket.

    2. HI Rob — Great idea ! .. So if i’m understanding you correctly , you would not add the cleaner and just run the water hose through the (2) hoses ? Then let it circulate
      through the heater hoses ( cold ) & just flush it ‘without’ running the engine first then ? .. OK ,, I think i got you .. You would only use the flush for the radiator itself then ? .. Would that be hot engine temp water , or doing that cold also ? Thanks much for a great idea .. I have to change out my upper hose & thermostat anyway .

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