How to Flush a Rusted Radiator

An efficient radiator cools your engine by circulating coolant through its pipes. It is important to keep it free of rust or blockages and it is even suggested that you flush and refill it every six months. It is easy to learn how to flush a rusted radiator but you will find that it is a bit messy so be sure to wear old clothing, keep children and pets away from your work area, and stay away from storm drains in case of any spills. Whenever working on your radiator, it is important that the engine is cold. Below you will find step-by-step instructions on how to flush your rusted radiator.

Step 1 – Drain Coolant from System

Park your car on a flat surface, turn on your heater, and then turn off your car. Be sure to set your emergency brake and place your car in park or in gear if it is a manual transmission. Let the engine cool.

Set your bucket under the radiator plug and open it. Allow all the coolant to drain into the bucket. If your engine also has plugs in the engine block, you can remove those too so that you can drain any remaining coolant. Once the flow has stopped, replace all the plugs.

Step 2 – Fill the Radiator with Cleaner

To remove the rust and sediment left in your system, you will now need to fill the radiator with radiator cleaner. You will use the mix of radiator cleaner and water as specified by the product’s manufacturer.

Step 3 – Run the Car with the Heater on

Turn your car on and turn on the heater to a high setting, following the instructions from the product’s manufacturer for the proper length of time to let it run.

Step 4 – Drain the Cleaner

After you have run the heater for the proper amount of time, you once again need to let the engine cool. Once it has cooled, place your empty bucket under the plug again, remove plug, and as before, allow all of the cleaner to drain out of the system.

Step 5 – Fill the Radiator with Water and Repeat

You need to flush the cleaner fully out of the system again, this time using only water in the radiator. Again, run the car with the heater on, allow the car to cool, and drain all the water out of the system once again by the plug.

Step 6 – Refill the Radiator with Coolant/Antifreeze

Always consult with the owner’s manual of your car for the proper coolant to water ratio. Being sure all the plugs are in, fill the radiator with the mix, and then fill the reservoir tank to the marked level (usually found on the side of the tank) with a 50/50 mix of coolant to water.

Step 7 – Run the Engine and the Heater

Start the car and run the engine to what is roughly a normal operating temperature. Run the heater on high again. This will circulate the coolant throughout the system. Be sure to check for leaks. You can now drive your car as normal.

Step 8 – Test the System

After several days of normal use, test the concentration of the coolant with either a hydrometer or test strips and adjust as needed.

Car Radiator Problems And The First Signs

A car’s radiator helps keep your car’s internal machinery at an acceptable temperature. When the radiator is not functioning optimally, your car can suffer damage that requires repair.

The Job of the Car Radiator

The radiator is critical to your car’s cooling system—its main goal is preventing overheating. It does this by constantly pumping cold air, cycled coolant, and water to the engine.

Telltale Signs of Car Radiator Problems

There are a few signs to watch out for that will let you know the radiator is in need of attention.


When the radiator is not functioning properly, this means the engine is not being cooled. That leads to the engine overheating, which affects car cabin temperature. An overheating engine therefore makes for an uncomfortable drive. If you notice your car is too hot, get it checked out right away. Overheating is dangerous to engine components and can lead to expensive damage.

Leaking Coolant

A simple check under the car will show signs of leaking coolant. Leaks can come from a variety of places on the radiator. If you see a pool of green or yellow liquid, you have a leak that needs immediate repair.

Coolant Light

When the “low coolant light” pops up on the dashboard, coolant needs to be added. It can also mean there’s a hidden leak, especially if you recently topped up your fluids. Either way, to be safe, have a mechanic check it out.

Gunk Buildup

When a radiator is not functioning properly, it can affect the coolant in a negative way, turning it into a brown goo. Sludgy coolant can’t make its way to the engine as efficiently, resulting a buildup of the substance on the radiator. This is another dangerous situation that can impact both the engine and the transmission.

Collapsed Radiator Hose

In the event the radiator breaks, it can also cause the hose to collapse or break (hoses can also break independent of their radiator).

Steam Emission

If you see steam seeping out around the hood or under the car, this means radiator trouble. Turn off the car and have it towed to the nearest reliable mechanic. Continuing to drive under these conditions can lead to additional damage.


When any of the above situations occur, the first thing you may want to do is pop the hood and inspect the radiator. Unless you notice the pool of coolant under the car or the “low coolant” light flashes on as soon as you start the car, do not attempt to check the radiator. If the car has been running, the components could be hot to the touch. Always let the car cool completely before doing any inspection that will require touching any of the car’s components.

If you don’t already have a roadside assistance membership, it’s a good idea to invest in one in case your radiator gives out while you’re out and about. To the extent possible, you should never drive a car when its radiator is experiencing issues.


Maintain a checklist of things to take a look at on your car between maintenance visits. From colored fluid on the ground, to gunky coolant buildup, spotting the signs of trouble early will help keep your car costs to a minimum.

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