What is the Best Way to Do a Radiator Flush?


Maybe you’ve taken your car in for some recent service and the mechanic let you know you needed a cooling system flush.  Or perhaps you noticed your vehicle was a little low on coolant and when you went to top it off you noticed some gunk floating in the overflow tank or radiator.  Or my personal favorite, you go to turn the heat on and you only get cold air even after your vehicle is well warmed up.

Cooling System FlushThese all are good indications that it may indeed by time for a radiator flush, or more accurately a cooling system flush.  If you’ve never flushed a radiator before or you don’t know how to flush a radiator, you’ve probably got some questions. Like, how did all the gunk get into your radiator? But how did all the gunk get into to your radiator, the cap has been on tight for years so there shouldn’t be any way for contamination to get in there right?  If all that gunk that clogged up your heater core didn’t come from outside your engine then it must be coming from your engine.  Is there something wrong, or is something about to break?

Why is a radiator flush important?

Before you go pulling the engine out of your car in search of bigger problems, lets figure out why your cooling system needs to be flushed even though it is a closed system.  Antifreeze, it turns out, is more than just green water that doesn’t mind the cold weather.  The main ingredient in Antifreeze is ethylene glycol and it is the chemical that allows antifreeze to stay liquid even in extremely cold temperatures.  Also included in antifreeze is a certain mix of lubricants and corrosion inhibitors.  Usually, water and steel don’t mix well as the steel will rust quickly.  The corrosion inhibitors in the antifreeze slow this process but never stop it completely.  Also, these corrosion inhibitors have a finite life span in your cooling system and after time will start to allow more rapid corrosion to occur.

The biggest cause for increased corrosion in your vehicles cooling system is improperly mixed antifreeze.  Many off-the-shelf antifreeze options require mixing with water before they are added to your vehicle.  If you use water from your tap to mix with your antifreeze, you are adding a whole new spectrum of chemicals to your coolant, many of which can be harmful to your vehicle.  Even filtered tap water has minerals dissolved in it, especially if you have “hard” water and many areas have high levels of iron or other metals in the water.  Also Chlorine is the most common chemical found in tap water used to kill bacteria and make sure the water is safe to drink.  Chlorine is also a very strong corrosive agent and if added to your vehicle’s cooling system can greatly increase corrosion.

Steel isn’t your only concern for corrosion particles in your cooling system.  Aluminum, copper and brass also can corrode releasing particles and the rubber hoses and gasket can also deteriorate over time adding to your cooling system gunk.

How do you flush a cooling system? (a.k.a. How to flush a radiator)

Cooling System FlushSo now that you’re worried about what may be lurking in your radiator, let’s look at how to flush your cooling system.  First, go to your favorite auto parts store and pick up a bottle of BlueDevil Radiator Flush.  BlueDevil Radiator flush has a concentrated formula with powerful cleaning agents designed to remove any gunk or scale from your cooling system without damaging any of the components.  Drain the coolant from your radiator by opening the drain valve on the bottom of your radiator.  Next drain the coolant from your engine block by opening the block drain also.  Make sure to catch all of the coolant in a drain pan, and take it to your local coolant recycling facility ort auto parts store.  After draining, close both drains.  Add BlueDevil Radiator flush to your radiator, then refill the cooling system with water.  Start your vehicle and let the engine idle for 15 to 30 minutes depending on how much long it has been since your last coolant flush.  Be sure to watch your vehicle’s temperature gauge carefully during this time to ensure it does not over heat.

Drain the water and flush solution in the same way you drained the original coolant.  For heavily corroded or high mileage vehicles, consider removing the hoses from your radiator and heater core and using a spray nozzle on a hose to inject high pressure water through the heater core, engine block and radiator.  This may help dislodge any stubborn build ups and particles and rinse any remaining flush solution from your cooling system.

Once your cooling system is empty, close the drains as before.  Refill your cooling system with the manufactures recommended type and amount of coolant.  Be sure to read the instructions on the antifreeze you purchase.  Some may require mixing with water, while others may be pre-diluted.  Often times it is less expensive to purchase antifreeze that requires dilution.  If you choose to go this route, purchase 1 gallon of distilled water for every gallon of antifreeze.  Using distilled water in your cooling system will ensure you are not adding any foreign minerals or chlorine to your vehicle.

Once your system is refilled, start your vehicle and let it idle until it reaches normal operating temperature.  Watch the temperature gauge carefully to ensure your vehicle is not overheating.  Let it idle at normal temperature for about 10 minutes then shut the car off and let every cool until it is cold to the touch.  Once everything has cooled, recheck the coolant level in your radiator and overflow reservoir and fill them to the recommended level.  Now you can close your hood and drive with confidence!

BlueDevil Products can be found on Amazon.com or at AutoZone, Advance Auto Parts, O’Reilly Auto Parts, NAPA, and other major auto parts retailers.

88 responses to "What is the Best Way to Do a Radiator Flush?"


  1. Md. Ekramul Kabeer on September 8, 2014 at 8:27 am


    Please please help me to choose a right coolant for my car.

    I amm using a old car. I am using red coolant. Which one is most expensive in our local market. The technician said, use green coolant as 50% with pure water.

    I want to know, what is the difference between green and red coolant?

    Can I mix them into the radiator?

    • BlueDevil Pro on September 9, 2014 at 8:15 pm

      Thanks for your question on our article “What is the Best Way to Flush a Radiator”! Using the right color coolant can be confusing. The end goal is to make sure your cooling system will not freeze and will keep your vehicle cool. As long as your cooling system is topped off and you use any type of pre-mixed antifreeze or concentrated antifreeze diluted with 50% pure or distilled water you will accomplish those goals.

      The colors of antifreeze are made by different manufactures and use different corrosion inhibitors for different materials in your motor. In general green type “universal” antifreeze will do a good job in the cooling systems of most engines in today’s vehicles it just may need to be changed, and your cooling system flushed more often (about every 2 years).

      For more information about when to use what type of antifreeze check out our article “Which Antifreeze Color Should I Use?” here: https://gobdp.com/blog/antifreeze-color-use/

      If you have any more questions feel free to comment on the bottom of that article.

      • John Chibanda on August 13, 2019 at 2:28 pm

        thanks a lot for good advice it woks

  2. Michael Powell on December 29, 2014 at 8:47 am

    Should I remove the thermostat before flushing? Recently bought a used jeep and cooling system was neglected. Thank you

    • BlueDevil Pro on December 29, 2014 at 11:14 am


      Yes you should remove the thermostat prior to flushing the system. You will leave the thermostat out for the entire BlueDevil process.


      • Michael Flynn on February 20, 2015 at 9:33 pm

        Remove thermostat? That’s a major separate task. If it is important why was it not included in your “how-to”? lesson above? I assume it is not necessary because the thermostat will open when the engine is running for 30 minutes and allow the flush solution circulate just fine.

        • BlueDevil Pro on February 23, 2015 at 9:35 am


          When using the “Mechanic Approved” 32 ounce BlueDevil Head Gasket Sealer it is required to remove the thermostat to ensure proper results. The product does partially react to heat so it is important that it is circulating through the system as the engine heats up.

          However, we do have a product called the BlueDevil “Pour N Go” Head Gasket Sealer that is an easy-to-use formula and does not require the removal of thermostat or a flush prior to use. This may be a better option for your vehicle.

          Thank You!


          • Alvaro on June 29, 2015 at 4:28 pm

            Hi blue devil pro, I have had over heating issues on my vehicle for the last 3-4 months and can’t figure out the problem, have had 4 compression tests done on it, coming back with normal results, I’ve changed the thermostat (twice) changed the radiator, reservoir, and cap, I open the bleeder valve and there’s a stream coming out, so I’m assuming it’s not my water pump, but I ran across your tips and was thinking maybe I have poor circulation in my system even if I already replaced my radiator, you think it would work in my case? Oh and my heater comes out cold, that was my main attraction to your advice, thank you

          • BlueDevil Pro on June 30, 2015 at 12:05 pm


            We recommend first having the water pump checked out as that may be the root of your problem. If it turns out that the water pump does not need to be changed then it is likely that you are having a restriction of flow within the cooling system. To help remove any buildup in the system we recommend running a bottle of the BlueDevil Radiator Flush through the system to help remove anything that may be causing a reduction in flow.

            Thank You!


          • Tracy A Holder on June 3, 2019 at 9:19 am

            You have to remove the intake manifold to get to many thermostat. Why wouldn’t someone just change the head gasket if they have to remove the intake anyway to get to the thermostat?

          • BlueDevil Pro on June 3, 2019 at 1:14 pm


            Some newer vehicles will require the removal of the intake manifold to get to the thermostat, however, most older vehicles do not require this. Feel free to contact our technical support line at 888-863-0426 with any other questions.

            Thank you!


  3. Kevin on July 23, 2015 at 5:29 pm

    Hi I have a ford ka sport 1.6 11year old my car does not have a temperature gauge but I can fill my water resivouire full to the brim as soon as I use my car the car will overheat to the point it is boiling within minutes of standing my engine fan will then kick in but car has had used too much water and as is still hot what do u recomend I do change the thermostat or try a system clean?

    • BlueDevil Pro on August 3, 2015 at 1:35 pm


      We recommend using the BlueDevil Head Gasket Sealer.

      Based on your description, it sounds like your vehicle may be getting combustion/exhaust gases blowing into the cooling system and creating pressure. To give yourself the best overall chance of BlueDevil working successfully, in addition to the directions, you should remove the spark plug from the cylinder with the leak; this will be the spark plug from the cylinder with a low compression reading. If you are not sure which one that is, you may pull all of the spark plugs and will sometimes notice one will have a white-crystal-like substance on it and/or may look dirty; this is the plug you should pull. Leave that plug out for the 50 minute idle in order to relieve the pressure from building up and thus allowing the product to seal properly.

      Feel free to contact us with any questions at 888-863-0426.

      Thank You!


      • David on December 23, 2015 at 10:27 am

        What should be used first gaskets sealant or radiator flush

        • BlueDevil Pro on January 5, 2016 at 8:43 am


          You would be using the Radiator Flushing Agent before applying the BlueDevil Head Gasket Sealer. It is important the is applied to a clean, free-flowing system. Feel free to contact our technical support line at 888-863-0426 with any other questions.

          Thank you!


  4. irfan on September 1, 2015 at 1:24 am

    Hello , I have Diesel Cumin’s Engine , its radiator is aluminium manufactured . I want to do a chemical cleaning of it . which chemical is best and what’s the procedure . can you help me out ?

  5. Ed Campbell on September 4, 2015 at 11:07 pm

    Is there any concern that these products can be a problem. I’m looking for a product I can circulate and clean piping to / from a lake cooling loop I’m using to cool my house.

    • BlueDevil Pro on September 15, 2015 at 12:40 pm


      No, there isn’t any concern in the Radiator Flush causing a problem. The product doesn’t harden or thicken in anyway, so it would not cause any adverse effects in the system.

      Thank you!


  6. Mark on December 6, 2015 at 10:24 am

    Since it’s already below freezing in my area, can I add the radiator flush to the coolant to do a “driving flush” for a few days before I have a power flush and refill done? (I know, I know…no such thing as stupid questions, etc.)

    • BlueDevil Pro on December 8, 2015 at 11:09 am


      Thank you for your question. You would need to drain the cooling system of antifreeze and simply add water to run with the BlueDevil Radiator Flush. The product would not be as effective running with antifreeze as it would be with just water in the system.

      Thank you!


  7. Rory on December 18, 2015 at 12:05 am

    I’m using this on a 1963 Studebaker. I do not know where the engine block drain plug is. Will that be a problem? Or will it still flush the radiator the block and heater core just fine? Thank you.

    • BlueDevil Pro on December 18, 2015 at 11:08 am


      Thank you for your question. You can simply drain the coolant through the bottom radiator hose. Once you add the flush and water to the system and let it circulate, you will drain all of that out and add water back into the system, repeating the process. You can continue to do this until you are getting nothing but clean water coming out. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  8. Les on December 22, 2015 at 9:10 pm

    With Blue Devil Radiator Flush …. can I do my flushing with water from a hose and then after all that is done ….. after I’m getting clean water ….. can I then use distilled water to flush the tap water residue out and then fill using 50-60% (of coolant capacity) full strength AF topping off with distilled.

    • BlueDevil Pro on December 23, 2015 at 4:47 pm


      Thanks for your question. Yes, you can use water straight from the hose to flush your cooling system without damaging anything. After you’ve completed the flush you can completely draining the radiator and block, leave the drains open, and use a small amount of distilled water to rinse the system. Then if you use distilled water to dilute your full strength coolant, your cooling system will be safe from any contaminants.

      Thanks again for your question!
      -BD Auto Pro

  9. DanWojack on February 18, 2016 at 7:19 pm

    I’m having issues with getting my engine temp. up to operating temp. of around 195degress. I changed the stat twice and changed the pump . also flushed the system on three separate times. and the heater core a forth time with extremely hot water .The system had the original Dex coolant in it with 160,000 on it and was rather brown and thick with particles in it. The rad cap showed caked on sludge as your picture does. I flushed each time till positive clear water and particle free ran through any opening . Any way I could get water to run through it I did , meaning back and forward flushes of heater core and engine and radiator . Will using this product show any results due to the fact I’m baffled as to why I cant get the engine hot or to over heat? Thanks Dan

    • BlueDevil Pro on March 3, 2016 at 5:53 pm


      Thanks for your question. If you’ve only flushed your system with water, then yes BlueDevil Radiator Flush will help clean your cooling system even more. BlueDevil Radiator flush will add a chemical cleaning to your system removing scale and allowing your engine to more efficiently transfer heat to the coolant. The other thing we’d recommend doing is taking measurement readings using a trusted instrument, like a inferred thermometer, at your radiator, near the thermostat housing and other places around your engine to make sure it isn’t your vehicle’s temperature gauge that is malfunctioning.

      Thanks again for your question!
      -BD Auto Pro

  10. Luke Smith on March 30, 2016 at 8:55 pm

    I really liked this post about how to flush out a car radiator. The photos with what to look for, and how it should be done is very helpful. So when I need my radiator worked on, I can have an idea of what they are talking about.

  11. Joe on May 21, 2016 at 10:47 pm

    Can one use more than one bottle of radiator cleaner to get a better results

    • BlueDevil Pro on May 23, 2016 at 2:35 pm


      Yes, you can use BlueDevil Radiator Flush to obtain a more extensive cleaning of the cooling system. Keep in mind, you may leave the product in your cooling system for a few days for a deeper clean.

      Thank you!


  12. Adam may on June 6, 2016 at 6:20 pm

    Have a big block Chevy no petcock on radiator or heater hoses how would you flush pull off bottom hose when done

    • BlueDevil Pro on June 10, 2016 at 9:56 am


      Yes, based on your description, you would want to drain everything out through the bottom radiator hose.

      Thank you!


  13. LeRoy Borden on July 31, 2016 at 2:04 pm

    Hi B D Pro
    A badly neglected (tap water, no rust inhibitor) motor will spall chunks of rust into the system, and the radiator may need to be back flushed and/or rodded out in addition to heavy chemical treatment. A new free flowing radiator can be plugged up and be compromised in the first few minutes of operation. to wit always flush before replacing said item.

  14. Chris on September 23, 2016 at 6:30 pm

    I would like to know a recommended way to dispose of the used flush and water. I live in California and don’t have a clue who to contact, especially someone with intimate knowledge of BlueDevil Radiator Flush ingredients.


    • BlueDevil Pro on September 27, 2016 at 10:40 am


      Please contact us at 888-863-0426 and we would be happy to help you out.

      Thank you!


  15. Steve Dobson on October 8, 2016 at 10:28 pm

    Have a new radiator for my PT Cruiser.I’ve removed the old rad.and wondering should I flush the engine/new rad or put they old one back for flushing.I’m sure the coolant was corrupted w/tap water and wrong coolant (non HOAT). I don’t want to compromise my new one with junk in the engine itself. The car shows no evidence of a head gasket leak (white smoke,oily water or watery oil). I forgot about the heater core also.

    • BlueDevil Pro on October 13, 2016 at 12:21 pm


      Thank you for asking about your PT Cruiser. Based on your description, it would be a good idea to perform a cooling system flush with the old radiator assembled. Once you have completed the flush, you wouldn’t have to worry about any debris coating your new radiator and would have a clean, free-flowing system from there. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  16. Frankie on November 8, 2016 at 12:38 pm

    I had a coolant flush at a local repair shop. I was using pink coolant and they switched to green. After a few hundred miles I check mycoolant level and the coolant in the reservoir was pink again. Is this a bad flush or could it be another problem. I thought coolant flushes replace all coolant in the car. Thanks

    • BlueDevil Pro on November 16, 2016 at 9:33 am


      There may have been a few trace amounts of your old coolant still in the block or elsewhere in the cooling system that was not removed during the initial flush. Does it look like an abundant amount of pink coolant or was it in spots? If the flush was performed properly, you should not be seeing any leftover amounts of your former coolant.

      Thank you!


  17. Richard Bastin on November 8, 2016 at 2:26 pm

    I have a keel cooler on a fishing troller made of 70 percent copper and 30 percent nickel. This functions the same as a radiator in a car but instead of useing air it uses it immersion in the ocean to do the cooling. Is your product compatible with this material

    • BlueDevil Pro on November 16, 2016 at 9:45 am


      Yes, the BlueDevil Radiator Flush is compatible with both copper and nickel. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  18. Barry on December 8, 2016 at 4:34 pm

    Cant get heat so was i was going to do a direct heater core backflush but cant get to the heater hoses to get them off——–and they make these clamps so hard to figure out sometimes so you cant do your own work. If I do a radiator flush as you suggested will that clean my heater core at all and how well in comparison to a direct back flush. If you say yes to some of that would it be best to do an extended driving flush instead of the the quick one

    • BlueDevil Pro on December 9, 2016 at 9:26 am


      When flushing the radiator, if the heat is on, the flush would circulate through the heater core. It would not be as extensive as back flushing the heater core directly, however, you may do an extended flush to give the vehicle a deeper cleansing.

      Thank you!


  19. Wes on January 6, 2017 at 11:55 am

    If I have already used blue devil head gasket sealer. Will using the flush ” undo” the results from the sealer?

    • BlueDevil Pro on January 6, 2017 at 2:23 pm


      No, using the BlueDevil Radiator Flush would not have any affect on the seal the Head Gasket Sealer has already created.

      Thank you!


  20. Chuck on January 11, 2017 at 10:03 pm

    I have installed a new therm. My petcock will not drain,and,I was told that 2 units of your product ran of 50 miles with the heater on high would solve the problem,is that true? I know you can’t answer that,but,will doing this hurt my therm or thr system.

    • BlueDevil Pro on January 12, 2017 at 9:08 am


      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!


  21. Quamie Redden on March 14, 2017 at 8:12 pm

    Can you drive your car around town for a few days with radiator flush inside the radiator to get a better cleaning?

    • BlueDevil Pro on March 15, 2017 at 9:49 am


      For an extended clean, yes, you may drive the vehicle with the radiator flush in the system. Keep in mind the flush is not acting as antifreeze, so if you are in a colder climate, you would want to get your regular 50/50 mix back in the system to avoid potential freezing.

      Thank you!


  22. Michael Ignacio on July 21, 2017 at 5:48 pm

    I have a FORD Eco Sport SUV. Can’t get to bottom hose. Can’t find a petcock to drain. If I flush with Blue Devil then when cool take off the upper radiator hose and run engine with garden hose in overflow tank till clear water will this be efficient?

    • BlueDevil Pro on July 24, 2017 at 11:30 am


      Thank you for asking about your Ford Eco Sport. Removing the flush the way you have described may not efficiently clear everything out of the system. We recommend taking the vehicle to shop to have them drain everything through the bottom radiator hose.

      Thank you!


  23. Steve McCarthy on July 25, 2017 at 8:54 pm

    OK, here’s a challenge. I’m getting a car back on the road that sat since ’84 in the desert. New core in the radiator, new water pump, t-state, hoses. Flushed about 10 times so far and it’s STILL puking GRAVEL out. No kidding! Can your stuff break up crud that bad?

    • BlueDevil Pro on July 26, 2017 at 9:26 am


      Based on your description, you may want to bring it to shop with a flushing machine, and have them backflush the system. It sounds like you may have a lot of corrosion and rust, which may not be able to be chemically dissolved.

      Hope this helps!


  24. Joe sanchez on July 29, 2017 at 2:51 pm

    I changed my radiator, thermostat and water pump… Bleed the lines for air and still overheating. I got the feeling im clogged in the motor itself, is this product a strong cleaner?

    • BlueDevil Pro on July 31, 2017 at 10:41 am


      Yes, the BlueDevil Radiator Flush would be able to help you with the type of restriction you have described. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  25. alex on November 13, 2017 at 10:43 pm

    I have a 2014 nissan altima I accidentally put washer fluid in coolant so i flushed my radiator and fill it with water…I let me vehicle run with heater on then shut it off do I drain it again? cuz when I refill it again it’s still coming out blue any suggestions?

    • BlueDevil Pro on November 14, 2017 at 9:27 am


      Thank you for asking about your Nissan Altima. Based on your description, we recommend flushing the system with the BlueDevil Radiator Flush, following the procedure until you are getting nothing but clean water coming out. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  26. Scott on December 28, 2017 at 11:40 pm

    Does a total cooling system flush also clear the heater core?

    • BlueDevil Pro on December 29, 2017 at 10:27 am


      Yes, as the heater core is a part of the cooling system, a total cooling system flush would go through the heater core as well.

      Thank you!


  27. john holmes on September 8, 2018 at 2:19 pm

    I have a 95 4.0L Ford Aerostar. The ATF cooler within the radiator failed and put ATF in my coolant system. I had been leaking ATF for several months but saw no evidence outside the engine, transmission or cooling system. It wasn’t until I had a heater hose fail that I discovered the problem. After replacing the hose I noticed ATF in my cooling system. At the time I didn’t know how that happened but them realized the ATF cooler of my radiator had failed and was the source of the ATF in my coolant system. The ATF in my coolant system probably caused the heater hose to fail by softening the rubber. I removed the radiator and decided to do a reverse cold flush with tap water through the heater core system (have a front and rear heater), through the water jacket with the thermostat removed (flushed in normal direction) with the original hoses. Also thoroughly cleaned the overflow reservoir. There was no radiator in the system at this point as I had a new one on order. After flushing the three sections of the coolant system I replaced all hoses as well as purchasing a new thermostat.
    Thinking that I had flushed the ATF out of the system I installed new hoses and a new radiator and filled the system with tap water. After starting the engine I noticed water coming off the back side of the engine which appeared to be a leaking head gasket. I then purchased so Blue Devil head gasket sealer followed all the directions on the bottle and the head gasket sealed in 15 minutes. Unfortunately through all this I discovered a bunch of ATF was coming out my overflow port of the radiator. Apparently the cold flush did very little in terms of getting the ATF out of my coolant system. I tried several full flushes with thermostat out of system and heater control and fan on max setting. Each time I got a lot of ATF out of system using tap water flush. After the 15th flush and days of time I decided to use Blue Devil flush with similar results. After the 20th flush again with tap water the globs of ATF were all but gone but the water was cloudy rather than clear. I then added two more bottles of the BD flush and then reverted back to tap water for and additional 5 flushes and a couple of short trips with the heater controls on max settings. Most recent flush does not have globs of ATF but water is still cloudy with smaller amounts of ATF.
    Just to verify it was ATF I let the water sit in the pan after the last flush and the water was clear underneath a surface of ATF. To make sure I did not have oil in the coolant I checked the oil indicator stick, spark plugs and drained oil as it was time for an oil change. To further my investigation I watched the water at the radiator cap to make sure it was not fountaining which could indicate a combustion leak which would put combustion gases in my coolant system as well as oil.
    Therefore the indication is that I still have ATF dissolved in my coolant after 25 flushes and four bottles of BD flush. I have concluded that the ATF is in suspension despite days of flushing the system. Right now I’m at a point of just keeping the last bottle of BD flush in the system as I take small trips with thermostat out and heater controls on max to see if its ever going to clear up to the point that the tap water will run clear. I’m surprised that the BD flush has not thoroughly cleaned my coolant system of the ATF.
    I suspect that because I had a ATF leak for several months that the ATF collected in every nook and cranny in my coolant system and that’s why its so hard to get it out of the system. Who would have thought a radiator failure would be the cause of ATF in the coolant system?
    Is there anything else I can do to get rid of the remaining ATF in my coolant system? Should I wait until the cloudiness is gone in the tap water coolant before adding distilled water and concentrated antifreeze?

    • BlueDevil Pro on September 10, 2018 at 10:31 am


      Thank you for asking about your Ford Aerostar. Based on your description, it does seem like it would be beneficial to leave the flush in a little longer, driving it intermittently over the course of a week or so. After, complete the draining procedure and flush the cooling system with water until you are getting nothing but plain clean water out. Yes, you should wait until the cloudiness in the water is gone before refilling the system with your distilled water/concentrated antifreeze mixture.

      Hope this helps!


  28. Autumn Jones on November 24, 2018 at 6:10 pm

    So do I remove the thermostat or not when doing the cooling system flush

    • BlueDevil Pro on November 26, 2018 at 9:33 am


      It is only a requirement to remove the thermostat if using the BlueDevil Head Gasket Sealer (32 oz. yellow label). If just simply flushing the cooling system, the thermostat may be removed, but it is not required.

      Thank you!


  29. Matt Adams on July 10, 2019 at 4:18 pm

    Is the Blue Devil flushing products safe for motorcycle engines that are aluminum?

    • BlueDevil Pro on July 11, 2019 at 8:51 am


      Yes, the BlueDevil Radiator Flush is safe and compatible to use on aluminum engines. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  30. Jeremie on August 1, 2019 at 12:16 pm


    I just purchased a 32 oz bottle of Blue Devil Radiator flush. I was reading in the posts and it left me with a few questions. I’m working on on 02 Escape 3.0 v6 that has been heating up only if i drive it above 55. It has a new water pump, a new motorad fail safe thermostat, new Coolant temp sensor and new hoses. I was thinking it may have a clog somewhere or buildup, so I’m going to run the flush through first. My questions are, Do I have to drain the coolant out first in order to use the flush? Do I need to remove the thermostat?

    • BlueDevil Pro on August 1, 2019 at 1:06 pm


      Yes, you would begin with a cool engine, removing the radiator cap and then draining the coolant out through the draincock/bottom radiator hose. You would then close the draincock and fill the system up with water. Put the radiator cap back on, start the engine, put the heat on to the max setting and let the vehicle idle for 10 minutes. You would repeat the drain procedure followed in step 1 before adding the BlueDevil Radiator Flush and topping off with water. It is not necessary to remove the thermostat if you are just flushing the system.

      Thank you!


      • Jeremie on August 1, 2019 at 1:27 pm

        Awesome, Thank you. I just didn’t want to go through the trouble of removing the thermostat. On this ford it is a pain to get to.

        Thanks again,

  31. Jim Mooney on August 11, 2019 at 8:46 pm

    I have a 1995 Pontiac Firebird with the 3.4L V6. It’s a recently acquired project car. It runs fine, but the radiator is full of a thick, mud-like sludge.

    Should I drain what’s in it and do a couple of fresh water flushes before I use the Blue Devil Radiator Flush? Since it’s so bad, I’d like to drive it for a few days before rinsing with distilled water and refilling with the proper antifreeze/coolant.

    Sound like a plan?

    • BlueDevil Pro on August 12, 2019 at 11:02 am


      Thank you for asking about your Pontiac Firebird. Your plan for flushing the system sounds like it would be fine. The only additional recommendation would be to follow the directions for the deeper radiator cleaning, driving your vehicle for 3-6 hours at normal driving conditions or intermittently over a period of a few days, with the BlueDevil Radiator Flush and water.

      Thank you!


  32. Sandra J Suarez on March 18, 2020 at 8:52 pm

    Hi I have a 1998 ford f150 my heater core supposedly is bad so while using blue devil radiator flush is it necessary to run the heater or can I just let it idle

    • BlueDevil Pro on March 19, 2020 at 11:13 am


      Thank you for asking about your Ford F-150. In terms of performing a radiator flush, it is not super important to run the heater, however, doing so would allow the flushing agent to go in through the heater core to remove any possible build up. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  33. Bob Tirevold on March 19, 2020 at 9:37 am

    So I screwed up and accidentally used an coolant jug that I had put used oil in and poured a “glug” (3-4 oz) of oil into my 2006 Mini Cooper coolant tank while vehicle was running.
    What is best way to flush this out?


  34. Chris Price on September 7, 2020 at 1:51 pm

    I plan to replace my hoses and do the flush in my Workhorse G.M. Motor home chassis. I read that the hoses could have contaminates embedded over time (they are original) so should i replace the hoses before or after the flush?
    Thank you,

    • BlueDevil Pro on September 8, 2020 at 10:14 am


      It may be a good idea to replace the hoses prior to flushing the system. If the hoses are old, and perhaps contaminates are covering up weak spots or areas of deterioration, flushing the system would remove those contaminates and allow water loss at those weak spots.

      Hope this helps!


  35. Austin mcinvale on March 10, 2021 at 11:41 pm

    So I have a 2001 dodge Dakota that I’m doing a engine replacement myself, the radiator is out of the truck now. I keep seeing that I have to drive around for 3-6 to completely flush the system. But my question is can I use blue devil radiator flush while the radiator is out and just let it sit overnight?. The previous owners put sawdust in the radiator to fix a blown head gasket but come to find out three pistons were broken and head gaskets were fine.

    • BlueDevil Pro on March 11, 2021 at 9:05 am


      Thank you for asking about your Dodge Dakota. Using the BlueDevil Radiator Flush in the method you’ve described would not be advisable. Circulation, heat, pressure, etc. are all factors that are allowing the flush to work as intended. It would not have the same affect just sitting in the radiator. You could, however, backflush the radiator specifically with the use of a flushing machine. You can check with your local shops to see if one is near.

      Thank you!


  36. rob on August 16, 2021 at 3:06 pm

    i have a 97 Yamaha Royal star 1300cc and the previous owner i guess mixed antifreeze now i have brown/blackish sludge in it.
    the block and heads are all aluminum, what do you suggest i use to flush it out?

    • BlueDevil Pro on August 16, 2021 at 4:50 pm


      Thank you for asking about your Yamaha. Based on your description, we recommend using the BlueDevil Radiator Flush & Oil Degreaser. This would be the best product to remove the brown/blackish sludge you discovered and is intended for deeper cleaning. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  37. Matt vespalec on November 19, 2021 at 3:17 pm

    how many times do you have to flush with water after putting and running the radiator flush? the flush itself was clear when it came out of the bottle.

    • BlueDevil Pro on November 19, 2021 at 3:42 pm


      You should only have to do the water flush once after running the BlueDevil Radiator Flush. When draining the water, as long as it is coming out as clean water, you should be good to go.

      Thank you!


  38. Jake on January 21, 2022 at 9:38 am


    I have a Buick Century 2002 that mysteriously leaked all the coolant and overheated. I filled it with tap-water weekly for two months before noticing the reservoir turning brown and some sludge under the radiator cap – I was causing rust. So then I flushed it twice with distilled water Blue Devil Radiator Flush and Oil Degreaser. Unfortunately, the petcock was clogged, and I don’t think the lower radiator hose drains the bottom of the radiator completely (it’s about 2-inches above the bottom).. After that, I added yellow universal antifreeze and noticed it formed thick brown/black sludge under the radiator cap, and now the car is now running slightly hot. I suspect rust particles were still trapped in the bottom of the radiator, because the water was still murky after the second flush.

    So I’m thinking the constancy of the antifreeze with the trapped rust in the bottom is turning to mud and clogging the radiator?

    I plan to run several more Blue Devil flushes out lower hose, hoping it will eventually clear out, and then run head gasket sealer. What do you think? Several months after the initial overheat, the EGR valve and catalytic converter completely clogged. Is this sign of leaking head gasket?

    Thank you.

    • BlueDevil Pro on January 21, 2022 at 10:13 am


      Thank you for asking about your Buick Century. Based on your description, it would be tough to say whether the brown/black sludge under the radiator cap is attributed to rust or something else. It could potentially be oil, however, we wouldn’t want to speculate as to what it is you’re seeing. Were you able to notice any improvement with flushing the system?
      Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  39. Mekkia on June 29, 2022 at 11:31 am

    Can you clean your heater core with Blue Devil Flush… if so is there a separate procedure… bought a car at auction and the cooling system seems funny…. water disappearing . no water in bottom of floor board is why I’m thinking heater core is clogged..

    • BlueDevil Pro on June 29, 2022 at 1:24 pm


      Yes, the BlueDevil Radiator Flush would be effective in cleaning the heater core. There are no separate instructions, as the flush would circulate through the heater core, as well as the rest of the cooling system. Feel free to contact our technical support team at 888-863-0426 with any other questions.

      Thank you!


  40. Joe on February 27, 2023 at 10:50 pm

    Hello, can I use this product with the radiator out of the car?

    • BlueDevil Pro on February 28, 2023 at 8:58 am


      If you were using a flushing machine, yes, you can backflush the radiator separately using the BlueDevil Radiator Flush. Otherwise, the radiator would need to be installed to allow for circulation and pressure.

      Thank you!


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