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.  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?

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.

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.

Coolant FlushOnce 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!


Pick up BlueDevil Radiator Flush at your favorite auto parts stores like:

  • Advance Auto Parts
  • Autozone
  • Pep Boys
  • Car Quest Auto Parts
  • Bennett Auto Supply
  • O’Reilly Auto Parts
  • NAPA
  • Prime Automotive

You can also purchase it online from the manufacturer.


Pictures courtesy of: www.cherokeeforum.com, autolistinc.com and mike-thompson.com

46 responses to “What is the Best Way to Do a Radiator Flush?

  1. Hello,

    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?

    1. 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://www.gobdp.com/blog/antifreeze-color-use/

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

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

      1. 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.

        1. Michael-

          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!


          1. 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

          2. Alvaro-

            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!


  3. 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?

    1. Kevin-

      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!


        1. David-

          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. 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. 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.

    1. Ed-

      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. 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.)

    1. Mark-

      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. 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.

    1. Rory-

      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. 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.

    1. Les,

      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. 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

    1. Dan,

      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. 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.

    1. Joe-

      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!


  11. 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.

  12. 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.


  13. 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.

    1. Steve-

      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!


  14. 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

    1. Frankie-

      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!


  15. 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

    1. Richard-

      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!


  16. 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

    1. Barry-

      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!


  17. 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.

    1. Chuck-

      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!


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

    1. Quamie-

      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!


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