How to Clean a Clogged Radiator? – 10 Steps to Remember

Written by

Bruce Sonnier


Marcus Dutton

how to clean a clogged radiator

Suppose you notice symptoms of clogged radiator in your car, such as overheating engine, coolant leakage, malfunctioning heater, etc. Then, you’ll need to act fast and do these steps on how to clean a clogged radiator.

It’s important to clean a clogged cooling system immediately to prevent any damage to your car’s radiator and engine, which would be costly to repair.

Step-By-Step to Clean a Clogged Radiator


What to Prepare

  • A bucket that can contain 2 – 3 gallons
  • Pliers or screwdriver
  • Plastic bottles to keep waste
  • Flushing solution – either a commercial radiator flush or baking soda for making a homemade solution
  • Distilled water both for flushing and rinsing the radiator as well as refilling with a new coolant
  • Funnel
  • New coolant, also known as antifreeze or radiator fluid

Step 1: Cool Down the Engine


Before you clean out a radiator, make sure to let the system and the engine cool down first for your safety.

Therefore, park the car, stop the engines, and give them several hours to cool down before cleaning.

Step 2: Put a Bucket Below the Drain Petcock

You need to properly dispose of the used fluid when you clean a car radiator to avoid polluting the environment and harming animals.

So you’ll need to catch the fluid with a bucket when you drain the system.

Typically, the coolant in the cooling system is approximately 2 to 3 gallons. Position a bucket that can hold that much right below the radiator’s drain petcock, usually near the driver’s side.

If there’s no petcock in the radiator, look for its hose at the bottom and place the bucket below it.

Step 3: Drain Out the Old Coolant

Twist open the fill cap, which can be found on the top part of the radiator.

Do the same for the drain petcock. But if there is no petcock in your radiator, detach the radiator’s hose at the bottom. You would need to use either pliers or a screwdriver to disconnect it, depending on how it’s attached.

Then wait for all the old coolant to flow out completely. If the fluid is not coming out, you can prompt drainage by poking and wiggling through the opening with a wire brush or piece of wire.

It would also be necessary to drain the reservoir tank for the coolant. Detach the reservoir hose connected to the radiator cap.

Then position the hose towards the bucket, so the fluid would be caught.

Finally, put the drain petcock and hose/s back in place.

Step 4: Store the Old Coolant in Some Plastic Bottles


You’ll need to dispose of the old coolant properly later, so pour it into some plastic bottles using a funnel to prevent spills.

You may consult your local hazardous waste management company, service station, the recycling center in your area, or an auto part store to dispose of it safely.

Step 5: Pour the Radiator Flush Into the Fill Cap

Make sure the drain petcock has been closed before you flush a clogged radiator. You’ll also have to dilute the flushing solution according to the product’s instructions.

It’s best to dilute the radiator flush with distilled water. Because, unlike tap water, it doesn’t have any minerals or impurities that can cause scale or corrosion in the system.

If you prefer a DIY solution, you may also clear blocked radiator with baking soda and water. The homemade radiator cleaning solution can be created by combining five teaspoons of baking soda for every liter of distilled water.

Once you’ve prepared your solution of choice, pour it into the radiator using a funnel. Then close the fill cap.

Step 6: Run the Engine for 15 Minutes

Let the engine run for 15 minutes to allow the solution to circulate in the system and dissolve the contaminants that have clogged it.

Moreover, the best way to flush the radiator is to set the heater on the highest level while running the engine, allowing the solution to flow better.

But also be careful not to let the engine get unusually hot; if it gets hotter than it normally does, it can get damaged.

So keep the temperature gauge in check as you do this step, and turn the engine off if it gets too hot.

Step 7: Drain the Radiator Again to Get Rid of the Contaminants


Let the engine cool down again before you resume to clean a coolant system. Also, don’t forget to place the bucket back under the drain petcock or bottom hose.

Once the engine is cool, open the fill cap and drain the petcock or detach the bottom hose again to flush out the contaminants.

It would also be necessary to store the used flush solution in plastic bottles.

Step 8: Rinse Down the Radiator’s Insides

Check if the radiator is finally unclogged by rinsing down its insides. Again, it would be best to use distilled water to prevent scaling and corrosion in the system.

You can tell that the radiator is unclogged when the water is flowing out clear and smoothly.

Step 9: Refill the Radiator With New Coolant and Distilled Water


After you fix a clogged radiator, you’ll then have to refill it with a new coolant and distilled water. To know what radiator fluid would be best to use for your vehicle, check the car manual or check with your local dealership.

The antifreeze and water should be a 50/50 mixture. However, there are also pre-diluted coolants in the market if you don’t want to deal with diluting.

Step 10: Run the Engine for 15 Minutes Again

The engine should be run once again for 15 with the heater on maximum heat to circulate the new radiator fluid and eliminate any air pockets.

It may be necessary to add more fluid, as the coolant level may drop in the process and be inadequate.

You should also check the temperature gauge to ensure the engine doesn’t overheat. If you notice it getting too hot, stop it.

An overheated engine could either be caused by inadequate coolant or air has gotten into the system.

  • If it’s the former, you simply need to add more radiator fluid.
  • If the problem is the latter, you can check the car manual to get rid of air or use compressed air or a vacuum-fill tool.



Is a Radiator Flush and Coolant Flush the Same Thing?

Yes, they are. One is just another name for the other, used to remove old coolants and flush out contaminants from the cooling system.

Why Does My Radiator Have Sludge in It?

Sludge can be caused by various substances that build up in the radiator. And it can be damaging to the engine, cooling system, heater core, and fluid passages.

It may be due to the contamination of oil or transmission fluid in the radiator fluid due to damage to the components of the engine or cooling system.

Corrosion in the radiator when the coolant degrades over time may also cause sludge.

Another cause will be the dropping out of additives if incompatible coolants have been mixed.

Those are just some examples, but exactly what caused it on your cooling system can be identified through a fluid analysis.

Once the cause is identified, fix it first. Then follow with a radiator flush.

Can Flush a Radiator Cause Problems?

Flushing a radiator will help keep it working properly and efficiently in protecting the engine and prevent any damage due to contaminant build-up.

However, it must be used carefully, as it’s an acid-based formula that can cause a series of problems if left in the cooling system for too long.

First, this acidic substance can melt the radiator, which would cause the coolant to leak.

And due to the leakage, the car’s AC system would also malfunction; instead of emitting cool fresh air, it would release warm dusty air.

It would also lead to an unpleasant, headache-inducing odor from the AC. This can put you and your passengers in an uncomfortable experience and at risk in your travel.

Will a Radiator Flush Fix a Clogged Radiator?

Yes, it can. A radiator flush can get rid of all kinds of contaminants in a car that can clog the system.


Knowing how to clean a clogged radiator will help prevent more serious damages to your car and also allows you to save money on maintenance, as you can do it yourself at home.

Moreover, it would also be necessary to also clean car radiator core to eliminate debris and contaminants that may get in the way of the proper airflow for efficiently cooling the engine.

Furthermore, you can learn other useful tips to clean inside of an engine, air filters, and clean an AC evaporator without removing it. Hope you will find what you need!

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