How to Flush a Radiator

Radiator FlushFlushing a radiator is a relatively simply job for a weekender mechanic with a basic tool set and a drain pan.  We will talk you through a procedure after we discuss the importance and frequency of performing a radiator flush.

Just flushing your radiator will probably help solve some of the problem you’re having, but in reality it is probably a full cooling system flush that will serve you and your vehicle better.  The radiator is the most accessible and visible part of your cooling system, so it is often the only part that we think to keep clean and well maintained.  Once the coolant in your vehicle exits the radiator, it travels through your water pump and into engine block and heater core before it returns to the radiator.  The water pump, engine block and heater also build up sediment, deposits and sludge so they need to be properly flushed as often as your radiator.  Luckily it is easy to flush the whole system at once.

Newer cars do not require coolant flushes as much as your grandfather’s 2 door Plymouth coupe did.  Old style brass or copper radiators combined with older water pump and coolant technologies lead to a lot of corrosion products and sludge build up in automobile cooling systems requiring very regular system flushes.  New vehicles with aluminum radiators and cylinder heads, along with better water pump bearing and seals, combined with new high quality corrosion inhibiting coolants have helped keep modern automotive cooling systems much cleaner.  You should check your vehicle owner’s manual to see how often your engine coolant should be replaced and perform a cooling system flush every time new coolant is added.  For most new cars and trucks the system should be flushed at least every 100,000 miles.  If you do not know when the last time your system was flushed, it would be better to  be safe than broken down, so perform a cooling system flush on your vehicle soon.

Cooling System Flush Procedure:

1.)    Ensure your vehicle is on a level surface, parked securely with the wheels blocked.  Also make sure your heater is turned all the way to “hot” and the fan is blowing.

2.)    While radiator is cool, remove radiator cap.  Position your drain pan under the radiator drain.  Open the radiator drain and allow coolant to flow out until it stops.  If your vehicle is equipped with an engine block drain, position your drain pan and open that drain allowing the engine block to completely drain as well.  Dispose of the used antifreeze at your local auto parts store or hazardous material transfer station in accordance with local law, and to protect our environment.

3.)    Fill the cooling system completely with water.  Start your engine and allow it to run at idle for 10 minutes, or until it has reached normal operating temperature.  Be sure to keep a careful eye on your engine temperature gauge during this step.  If your vehicle begins to overheat, turn the engine off immediately and let it cool.

4.)    With your radiator and engine cool again, drain the water from the cooling system just like you did in step 1 draining the radiator and the block.

5.)    With all the drains closed, add BlueDevil Radiator Flush to your radiator and top off the system with water.  Once you have about 2 gallons of water in the cooling system start the engine and let it warm up.  As it warms continue to add water to the radiator until you see water flowing through the radiator and the upper radiator hose is hot.  Top off the system with water and replace the radiator cap.

6.)    Let your engine idle with the radiator flush inside for at least 10 minutes, but time and weather permitting run your vehicle for 3-6 hours with the radiator flush and water solution in your cooling system.  This will provide a deep clean and restore your cooling system to top efficiency.  While driving, keep an eye your temperature gauge to make sure it doesn’t overheat and make sure the outside temperature does not drop below 32 degrees to prevent freezing.

7.)    With the engine again cool, drain the Radiator Flush and water mixture.  With all the drain plugs open, flush the system thoroughly with water allowing it to flow into the radiator cap and out of the radiator and block drains until clear water runs freely out.

Cooling Flush

8.)    Close all drain plugs and add the manufacturer’s recommended type and amount to your radiator.  Just like step 5, you may have to add most of the antifreeze, then start and run the engine up to operating temperature to allow coolant to flow through the engine and radiator removing bubbles and allowing room for all the antifreeze.

It is best to purchase all the products you will need before starting any project.  You can pick up the required amount of antifreeze at your local dealership or auto parts store.


You can order BlueDevil Radiator Flush online. or it can also be ordered at your participating local retailers:

  • Bennett Auto Supply
  • Prime Automotive Warehouse
  • NAPA
  • PepBoys
  • CarQuest Auto Parts
  • Advance Auto Parts
  • AutoZone
  • O’Reilly Auto Parts

Pictures provided by: and

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40 responses to “How to Flush a Radiator

  1. I have a 2002 Ford Taurus with 154408 miles. I had minimal heat from the heater. I have always been skeptical about what I call most products Miracle fix in a bottle. But I decided to give this product a try. Followed direction on the bottle and within hour and a half of idle and running engine at 2500 to 3000 rpm occasionally the water went from green tint to black and now have 100% heat from heater. This product saved me a lot of time and money from replacing heater core. I highly suggest this product.

  2. I have added cleaner to the rediator now on a 1943 jeep how can I drain the engine block or does the block drain with the radiator ?

  3. I used this product over the weekend (actually roommate did). I now have a bunch of smoke coming out of tailpipe. Did he do it wrong?

    1. Heather-

      White smoke coming from the exhaust pipe is a tell-tale sign of a blown head gasket. Was your roommate flushing the radiator in preparation of using the BlueDevil Head Gasket Sealer? Please contact our technical support line at 888-863-0426 so that we can get a better understanding and be able to make any appropriate recommendations.

      Thank you!


  4. Just need a confirmation. If my overflow reservoir had a thick layer of sediment (thinking rust) it’s safe to assume there’s probably a layer at the bottom of my radiator. Time for a new radiator?

    1. Jonathan-

      You are correct. There is a good chance that if you found a thick layer of sediment in your reservoir, that the substance would also be in your radiator. If you are thinking it is rust, it would be a good idea to have the radiator replaced. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


        1. Nick-

          For deeper radiator cleaning, drive your vehicle for 3-6 hours at normal driving conditions or intermittently over a few days, if weather permits. Feel free to contact our technical support line at 888-863-0426 with any other questions.

          Thank you!


  5. How does the hardness of the water affect the flush process? My tap water is pretty hard, leaves a line when boiled in a pan. If I leave it in and run for the 3-6 hour step, would that cause problems? Would it be best to use distilled water? Also, I assume that all the drainings in the flush would be considered hazardous waste, like the original drain with the coolant. Thanks.

    1. Bryan-

      It is not required that you use distilled water when adding BlueDevil Radiator Flush. Using hard water would not affect the use of BlueDevil Radiator Flush.

      BlueDevil Radiator Flush contains non-hazardous chemicals. However, any remnants of antifreeze within the mixture would be considered hazardous.

      Thank you!


  6. Is the Blue Devil Radiator flush safe and effective on a diesel engine? (6.0 Power Stroke)
    I have an occasional overheat indication when towing 10,000# up a steep grade in hot weather, otherwise the cooling system works within specifications.
    With a 24 qt cooling system, will two bottles of flush be enough to do the job or would I need more?
    This vehicle has 96,000 miles on the clock.
    Thank you.

    1. R Kaufman-

      Yes, the BlueDevil Radiator Flush would be effective on a diesel engine. One bottle of the Flush will treat up to 3 gallons, so you would need two bottles for a 24 quart cooling system.

      Thank you!


  7. Hi i have a hyundai veloster 2013 and i just used blue devil head gasket sealer and i didnt drain flush the cooling system and its blowing smoke and when i drive the car it seems fine but when i stop it blows smoke and the fan goes on and my tempeature goes up

    1. Kevin-

      Thank you for asking about your Hyundai Veloster. Please contact our technical support line at 888-863-0426 so that we can get a better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


    1. Jon-

      BlueDevil Radiator Flush restores efficiency to vehicles by helping remove grease, rust, grime or any other buildup that occurs during normal vehicle use. Our specially formulated flush works well in all vehicles, especially those with high mileage warranting a deep clean. Flushing your cooling system with BlueDevil Radiator Flush will impact your vehicle’s performance and add life to your car.
      For best overall results, we recommend using the flush with only water in the system, however, you may use it with an antifreeze mixture in colder climates.

      Thank you!


      1. Is there any risk involved if you are unable to use water and just add the blue devil radiator flush to your 50/50 antifreeze?

        1. Anthony-

          Adding the BlueDevil Radiator Flush to 50/50 antifreeze instead of water would not cause any harm, however, it would be limiting the effectiveness of the product. Feel free to contact our technical support line at 888-863-0426 with any other questions.

          Thank you!


  8. My car was getting no heat due to plugged heater core. I used this and heat came back. I was very pleased with Blue Devil Radiator Flush due to it saving me a bundle of money.

    1. Mark-

      The BlueDevil Radiator Flush would not be acting as antifreeze, so it should be drained out and refilled with your regular antifreeze mixture. For extended cleaning, you can drive the vehicle for 3-6 hours with the flush in the system. Do not let the cooling system temperature fall below 32 degrees F.

      Thank you!


  9. I have a 2002 olds silhouette, I’ve used your HGS to fix the head gasket, worked so far until today. Engine overheating, I think the thermostat is stuck. I plan to replace it. Flush system. Will I need more HGS after the flush? Any tips when flushing would help. Thermostat is in a hard to get spot.

    1. Bradley-

      Thank you for asking about your Oldsmobile Silhouette. You should not need anymore of the BlueDevil Head Gasket Sealer at this point. Flushing the system would not undo any of the seal the product has already created. Once the thermostat is replaced and the system is flushed, the engine should cease overheating. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  10. Many modern vehicles do not have a radiator cap — the cooling system is sealed up to the coolant overflow reservoir. How does one properly flush a sealed system such as this, and particularly how does one avoid air pockets in the cooling system?

    1. Kirk-

      If your vehicle only has a reservoir/overflow rather than a radiator cap, instead of pouring BlueDevil through the reservoir/overflow, with the car off and engine cold you should disconnect the top radiator hose and add the product there; do not pour it into the overflow bottle. Once it has been added reconnect the hose and start the flushing process from that point.

      Thank you!


  11. My mechanic did the treatment on my car this past Monday, which is 5 days ago. My question is!! Do I add water to the radiator or do I just leave it alone? At first he said not mess with it, then yesterday another co worker of his said to check it today before turning the car on… And if the radiator needed water. To add some to it, I’m confused and don’t know what to do.

    1. Nereyda-

      After the mechanic flushed the system, did they re-fill it with your regular 50/50 mix? Please contact our technical support line at 888-863-0426 so that we can get a better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


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