Time for a Coolant Flush? How to Flush the Coolant in Your Car

If you want to know if it’s time for a coolant flush or how to flush the coolant in your car, this article and videos reviews how you can tell when it’s time to flush the coolant and what you’ll need to do to remove and add new coolant in your car.

How to Do Your Own Coolant Flush

Performing a coolant flush

When Should You Flush Your Coolant?

Coolant, also known as antifreeze, keeps the engine from overheating. Over time, contamination and sediment can deteriorate the coolant. As it deteriorates, it may cool the engine less effectively.

Check your owner’s manual for recommended intervals of when you should change the coolant. Your owner’s manual will also have information on what kind of fluid to use, how much fluid to use, and how much time or mileage should pass before changing it.

Once the coolant shows signs of going bad, it’s time to change it.

Tip: Mixing different kinds of coolant can cause problems like corrosion and clogging.

How Can You Tell If the Coolant Is in Bad Condition?

Dirty, sludgy coolant
Dirty, sludgy coolant

Coolant that is in bad condition will be a different color than the type recommended for your vehicle. It may be dirtier, darker, sludgier, and/or smellier.

If you don’t know when the cooling system was last serviced, there are different ways you can test the coolant. You can check and see if it’s a brown or darker color, which means it needs to be changed, or you can use an antifreeze tester to find out what condition the coolant is in. If the coolant is in really bad condition, you can also use a cleaner to remove it from the system.

Read more about how to test the coolant with an antifreeze tester

Are Coolant Flushes Necessary? How Often Should I Flush the Coolant?

Coolant flushes are a necessary service that will need to be done periodically. The owner’s manual will have recommended intervals for when the cooling system should be serviced. If the coolant is not flushed regularly, it can cause corrosion, leaking, and other problems like an overheated engine.

How to Flush the Coolant

Steps for flushing the coolant

  1. Let the System Cool Down and Inspect the Coolant

    Wait for the cooling system to cool. Do not remove the radiator or coolant reservoir cap with the system hot. The fluid can spray up and cause major burns if the system has not cooled down.

    Find the radiator cap. If there is no cap on the radiator, remove the reservoir cap and check the condition of the coolant in the reservoir.

    Check the condition of the coolant. If it is sludgy, discolored, or has contaminants, replace it.

    If the coolant has build-up and is sludgy, clean the system with a cleaner by following the directions on the bottle. Otherwise, the coolant can be drained and refilled.

  2. Drain the Radiator

    With the engine cold, remove the radiator cap. Check the radiator for drains, which are usually on the ends of the radiator. If the radiator doesn’t have a drain, you’ll need to remove the lower radiator hose.

    The lower radiator hose can be removed with a pick or pry bar. Loosen the clamp and slide the hose off. Have a drain pan ready since the coolant will drain quickly.

    The radiator will drain about half of the coolant. You may need to drain coolant from the engine block. If you cannot drain coolant from the engine block, you will need to refill and drain the cooling system a few times to remove the bad coolant.

  3. Drain the Engine

    There may be a drain on the side of the engine block. For example, if you have a V8 engine in a truck, there will be a drain on each side. This will allow you to drain most of the coolant out of the system.

  4. Remove Coolant from the Coolant Reservoir

    With all of the coolant out of the radiator, extract the rest of the coolant from the reservoir. You can remove the coolant with a fluid extraction pump, or you can remove the coolant reservoir from the vehicle and drain the coolant into a drain pan, and then reconnect the reservoir.

  5. Fill the Radiator with Coolant

    Fill the radiator with coolant. If the radiator doesn’t have a cap, fill the reservoir with coolant.

    There are special coolant filling funnels that can make this process go easier. Connect this to the radiator and fill it with the appropriate coolant that’s specified in the owner’s manual. Some coolant will come prediluted, so there’s no need to mix water with it. If you do have to mix water with the coolant, make sure it’s distilled water so there’s no extra elements added to the mixture.

  6. Run the Engine for 10 Minutes and Let the Coolant Circulate

    Start the engine and run it for 10 minutes to circulate coolant. This coolant will mix in with the old coolant if the engine block wasn’t drained.

    Monitor the coolant temp sensor on the dash and make sure it doesn’t enter the red mark to prevent any damage to parts in the system.

    If you only drained the radiator, let the vehicle cool down, drain the coolant again, and add more coolant. Run the vehicle again for 10 minutes. Once the vehicle has cooled down, check the coolant level and add more if needed.

    To bleed the system of any air, learn more in this article and video

  7. Place the Old Coolant in the Old Container and Dispose It

    To dispose old coolant, place it in the old jug and bring it to a recycling center that recycles coolant.

    Read more on how to dispose of automotive fluids

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Time for a Coolant Flush? How to Flush the Coolant in Your Car - 1A Auto
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Time for a Coolant Flush? How to Flush the Coolant in Your Car - 1A Auto
Learn how to tell if it's time for a coolant flush and how to flush the coolant in your car with these tips and instructions from expert mechanics
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1A Auto
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