How to Perform a Radiator Flush

Your vehicle’s radiator is a heat exchanger designed to dissipate heat as antifreeze, or coolant, passes through it. Coolant travels throughout the cooling system to carry excess heat from the engine to the radiator to help prevent overheating. This helps the engine maintain a safe operating temperature to improve performance and limit the risk of engine damage. Flushing and refilling your vehicle’s antifreeze is typically recommended every five years, and is important for protecting your engine and other components from overheating, damaging contaminants, and corrosion. You can find the manufacturer-recommended service intervals in your vehicle’s owners manual or service manual, but this maintenance task can be performed as often as needed to ensure optimal cooling system performance.

Tools & Materials

Safety Glasses Safety Glasses

Gloves Gloves

floor Jack Jack

jack stands Jack Stands

O'Reilly Pre-Mixed Coolant Antifreeze Pre-Mixed Antifreeze

DIY Flush & Fill Radiator Cleaner Radiator Cleaner

Drain Pan Drain Pan

Garden Hose Garden Hose

Funnel Funnel

How to Flush and Refill Antifreeze

This page and video will show a radiator flush performed on a 2009 Honda Accord, but the steps are similar for most vehicles. Before completing the job, we recommend taking a look at your vehicle’s owners manual or service manual to review the manufacturer's recommended steps for draining, refilling, and bleeding your cooling system. If you don’t feel completely comfortable doing this maintenance task yourself, one of our parts professionals are more than happy to refer you to a professional technician in your area.


Locate antifreeze reservoir in car before you flush coolant system

Step 1: Prepare the Vehicle


Before starting a radiator flush, make sure your engine is completely cool. If you don’t let your engine cool, system pressure and hot coolant can cause injury. Once the engine is cooled down, make sure to put on your gloves and eye protection before opening the system.

Do It Right: Jacking up the front of your vehicle and placing it on jack stands will make it easier to work underneath the radiator. If you have a vehicle with plenty of ground clearance, jacking up the vehicle may not be necessary.

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remove the fill cap on your antifreeze reservoir

Step 2: Find and Remove Your Radiator Cap


Open your hood and locate your antifreeze reservoir or radiator cap. To drain your old antifreeze, start by removing the fill cap from the reservoir or radiator. The fill cap can be found on the radiator itself, or on the reservoir near the firewall or the sides of the engine compartment.
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small shut-off valve, the petcock

Step 3: Locate the Petcock / Radiator Drain Valve

Locate the petcock, which is a small shut-off valve, which will be located on the bottom of the radiator. On some vehicles, the petcock may have a small plastic cover. If so, remove the cover with a screwdriver and set it aside.
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Antifreeze draining into drain pain

Step 4: Drain the Old Antifreeze

Place a drain pan under the radiator and open the petcock to let the old antifreeze drain. Typically the petcock valve can be turned counterclockwise to open it and allow coolant to flow through. Depending on how the vehicle’s engine bay is laid out, it may be beneficial to use a small length of hose to connect to the end of the petcock and direct coolant into a drain pan. Once the antifreeze is done draining, close the petcock.
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add radiator cleaner and replace radiator cap

Step 5: Add Radiator Flush/Cleaner

Next, add radiator cleaner and water according to the manufacturer's recommendations or product directions, and replace the radiator cap.

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start the vehicles engine

Step 6: Start Your Vehicle

Start your vehicle and turn your heater on high until the engine reaches normal operating temperature. After letting it run, shut your engine off and let it cool down completely.
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open fill cap, drain radiator fluid from car cooling system, and close the petcock

Step 7: Drain the Radiator Cleaner from the System

Remove the fill cap and open the petcock to drain the system again. When it’s done draining, be sure to close the petcock.
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use a garden hose to fill the cooling system with water

Step 8: Fill the Cooling System with Water

With the fill cap open, use a garden hose to fill the system with water according to the manufacturer’s specifications, and replace the radiator cap.
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start the vehicles engine

Step 9: Start Your Vehicle

Turn on the engine and let it run until it reaches normal operating temperature. Then turn off the engine and let it cool down completely.
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open the petcock and drain cooling system

Step 10: Drain the System Again

Remove the radiator cap, open the petcock, and drain the system again, making sure to close the petcock after it’s drained completely.
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use a garden hose to fill the cooling system with water

Step 11: Repeat the Water Flush Process

Repeat steps 8 through 10 to perform one final water flush.
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refill the car cooling system with O'Reilly antifreeze pre-mixed coolant

Step 12: Refill the System with Antifreeze

Now that your system has been flushed and drained, you can add the appropriate type of antifreeze or coolant for your vehicle. Concentrated and pre-mixed antifreeze is available in a variety of formulas that may be vehicle specific, so be sure to check your vehicle’s owners manual to ensure what type you need. If you're using full-strength antifreeze, make sure to dilute it with water before refilling the system. The proper ratio will typically be 50/50. If you're using a pre-mixed antifreeze, you won't need to add water to the system, but you may need more than one jug to ensure a complete fill. To learn more about different types of antifreeze, check out our article.
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start the vehicles engine

Step 13: Let the Engine Run

Leave the radiator cap off, start your engine, and let it run until the engine reaches normal operating temperature. Add coolant as needed to restore the level, then replace the radiator cap. Let the engine run for another 10 minutes, then check under the vehicle for any leaks.
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check to see if your coolant level is to the proper level

Step 14: Check the Antifreeze Level

Shut off the engine, and once it’s cooled down completely, double-check the antifreeze level to see if any needs to be added. If it’s at the proper level, you’re all done.
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Additional Resources

Shop Antifreeze

Shop Antifreeze
Shop Heating & Cooling

Shop Heating & Cooling
How To Check & Test Antifreeze For Winter

How to Test and Check Antifreeze for Winter

The automotive repair work depicted in this series is performed under the direction of the manufacturer of the product featured. Prior to undertaking any of the demonstrated repairs on your vehicle, we suggest you consult with a certified mechanic or another professional who can adequately advise you of the proper repair or remedy required. O’Reilly Automotive Stores, Inc. and its affiliates (“O’Reilly”) disclaims any responsibility for injury or damage resulting from a viewer’s attempt to recreate the repairs shown in this series.