Flushing 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.
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.
Pictures provided by: mike-thomson.com and www.totalautowny.com
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.
85 responses to "How to Flush a Radiator"
85 Comments
Leave a Reply
Related Articles
I have a 1998 ford taurus. Doing a coolant flush do I have to remove the thermostat during this flush?
Donald-
Thank you for asking about your Ford Taurus. You do not have to remove your thermostat before flushing your cooling system.
Thank you!
-BDP
Thank u very much
You don’t have to but if you want the water to freely flow and clean better you can remove it, only if it’s easy to get to.
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.
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 ?
Leonard-
It will be very difficult to get 100% of the fluid out of your engine block. However, it is not necessary to remove 100% of the fluid.
Thank you!
-BDP
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?
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!
-BDP
How is this applied with a 2000 Pontiac firebird ?
OJ-
Thanks for asking about your Pontiac Firebird. The directions for the BlueDevil Radiator can be found here, http://store.gobdp.com/radiator-flush-directions/ . The directions would not be any different based on your vehicle. Feel free to contact our technical support line at 888-863-0426 with any other questions.
Thank you!
-BDP
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?
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!
-BDP
How long can I let it sit
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!
-BDP
So it is OK to have the Flush inside the cooling system for a few days? I don’t drive long distances, so to run my vehicle for 3 to 6 hours will takes several days.
Lucita-
Yes, it would be fine to leave the flush in the cooling system for a couple ideas, unless you are in an area where the temperatures will fall below 32 degrees Fahrenheit. In that case, you would want to drain the flush out and refill it with your regular 50/50 mix.
Thank you!
-BDP
Jonathan-
It is likely that there may be some sediment in the radiator if you are seeing a good amount in the reservoir. Before you replace the radiator you good attempt to flush the cooling system. We recommend using our flush: BlueDevil Radiator Flush (http://store.gobdp.com/radiator-flush-00204/). This product may eliminate the need for a new radiator.
Thank you!
-BDP
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.
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!
-BDP
Just use distilled water, for a mere couple bucks, it’s worth doing the right way. Particularly if you want a very thorough clean of all sediment and debris without risk of more buildup in the future.
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.
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!
-BDP
how do i flush the radiator and then put in the sealer ( Blue Devil?
Roy-
Yes, prior to adding the BlueDevil Head Gasket Sealer http://store.gobdp.com/head-gasket-sealer-38386/, you would be removing your thermostat and performing a radiator flush. Feel free to contact our technical support line at 888-863-0426 with any other questions.
Thank you!
-BDP
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
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!
-BDP
How is your product superior to your competitors?
Also, for cold weather flush, can this be used with antifreeze mixture?
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!
-BDP
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?
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!
-BDP
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.
Richard-
It is excellent to hear of the success you had using the BlueDevil Radiator Flush! Your vehicle should be good to go at this point.
Thank you!
-BDP
can flush be left in system or must be it be drained out
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!
-BDP
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.
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!
-BDP
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?
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!
-BDP
My 2000 pontiac sunfire only has reservoir, but is full of sludge, either oil or rust. It does have a blown head gasket in which is what I’m trying to fix but need to flush system first. Will it hurt to add into reservoir since its so dirty as well?
Jonathan-
Thank you for asking about your Pontiac Sunfire. Based on your description, we recommend using the BlueDevil Radiator Flush & Oil Degreaser. This would be best to use, especially if it is oil in the cooling system. BlueDevil Head Gasket Sealer is only intended for water/coolant leaks. 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 recommedations.
Thank you!
-BDP
Hello. I am swapping an engine and want to thoroughly clean the radiator before reinstalling it with the new engine. Is the Blue Devil cleaner/flush/degreaser appropriate for the radiator not installed? Can I use it to clean the radiator out of the car and if so, is there any particular procedure other than putting it in with water and sloshing it around to ensure it’s mixed and then let it sit and drain?
Bruce-
You could use the BlueDevil Radiator Flush & Oil Degreaser on a radiator that isn’t installed, however, you would need a flushing machine to successfully accomplish cleaning the radiator. It would not have the same effect by just sitting/soaking in the radiator. Heat, pressure, circulation, etc. are all factors that are needed. You could try flushing the radiator before swapping the engine versus taking the radiator to a radiator shop to use a flushing machine. Just another option for you.
Thank you!
-BDP
Thank you!
-BDP
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.
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!
-BDP
Will this flush be harmful to head gaskets? I don’t want to use this product and end up with problems.
Dale-
No, using the BlueDevil Radiator Flush would not be harmful to head gaskets, or any other component in the cooling system.
Thank you!
-BDP
I have a 2011 Jetta 2.5L …
I read that the capacity of the cooling system is 10 quarts…
Is one container of Blue Devil Flush correct to use ???
Mark-
Thank you for asking about your Volkswagen Jetta. Yes, one bottle of the BlueDevil Radiator Flush would treat a cooling system up to around 3 gallons, so it would be sufficient enough to treat your 2.5 gallon system. Feel free to contact our technical support line at 888-863-0426 with any other questions.
Thank you!
-BDP
how long do I have to leave blue devil flush in my rediator
Johan-
Were you attempting to do a deeper radiator cleaning? If so, we recommend driving the vehicle for 3-6 hours at normal driving conditions or intermittently over a period of a few days, if weather permits. Feel free to contact our technical support line at 888-863-0426 with any other questions.
Thank you!
-BDP
For the radiator flush,I can only get the antifreeze out the radiator I cant get the screws out to flush the rest of the antifreeze mixture out in the block and heater core area..can I add your product with just the antifreeze out in the radiator and reservoir..
John-
Yes, that would be fine. Simply remove the radiator cap and open the radiator draincock and drain the cooling system and then start the process from there.
Thank you!
-BDP
I am trying to stop a possible leak with my heater core. Its a v8. Do i need to do a radiator flush before i add bluedevil pour n go head gasket sealer into the radiator?
Jesse-
If the system is contaminated/dirty, flushing the radiator prior to adding BlueDevil would be recommended. The Pour-N-Go Head Gasket Sealer is intended for use in a 4 or 6 cylinder engines, so if using it on a V-8, you would need at least two bottles for the larger engine.
Thank you!
-BDP
my car blew a head gasket and has since been repaired, but there was a significant amount of trial and error before it was determined to be a head gasket. during this process water pump was replaced. there was a significant amount of oil in the cooling system and has mostly been flushed out, I’m wondering if this product will help me in removing any leftover oil still in the cooling system. I plan to replace all my cooling system hoses and water pump again if necessary after this flush if it will help.
Lakota-
Based on your description, the BlueDevil Radiator Flush & Oil Degreaser (https://gobdp.com/product/radiator-flush-oil-degreaser/) would be the product you would want to use. Feel free to contact our technical support line at 888-863-0426 with any other questions.
Thank you!
-BDP
While flushing a project vehicle I got deployment orders. Do I need to drain Blue Devil radiator flush and start over when I get back home or can I let it sit in my system for a month or so?
Joe-
We wouldn’t recommend leaving the flush in the radiator for more than a few days. Based on your description, you would want to drain the flush out and start over once you return.
Hope this helps!
-BDP
I have a 2012 BMW 535i that has intermittent overheating problems and intermittent heater problems. No hot air from heater from time to time. The thermostat seems to work only some of the time. Im guessing there might be debris in the system or the thermostat is sticking sometimes. Will Blue Devil help with this problem? Trying to avoid thermostat/waterpump replacement.
Devin-
Thank you for asking about your BMW 535i. Have you noticed a loss of water/coolant? If not, you may have some kind of a restriction in the system, causing the intermittent issues you are experiencing. You can remove the thermostat and put it in boiling water to make sure it is opening at the correct temperature. If the thermostat appears to be functioning properly, flushing the cooling system with the BlueDevil Radiator Flush would be your next best option.
Thank you!
-BDP
its 20 degrees out and I need to flush my radiator. I’m a little worried about using water? can I use anti with the Blue Devil flush mix instead (its the 3 in 1 mix)
Jason-
It will still be effective with antifreeze in the cooling system. However, for maximum cleaning we recommend using it with water.
Thank you!
-BDP
Is a little bit of sediment in the anti-freeze normal after doing a flush or is it a sign it needs to be done again or a sign of a deeper issue?
Sandy-
If you are still seeing a little sediment, you may want to complete the flush procedure again. Once complete, you should be getting nothing but plain, clean water coming out of the bottom radiator hose. Feel free to contact our technical support line at 888-863-0426 with any other questions.
Thank you!
-BDP
Hello
I added blue devil to a 2018 mustang gt but didnt drain it..it was mixed with coolant.. before i took it in to have the water pump changed.
I thought they would do a radiator flush but only did a drain and fill. So, there is some blue devil left in the coolant. However, it is an over 3 and a half gallon system. The coolant looks clean.
My question is will any left over blue devil damage the head gasket or anything else in the system?
Thank you.
Steve-
The BlueDevil Head Gasket Sealer only goes through one heat cycle. After the initial heat cycle has completed, the BlueDevil wouldn’t continue to react or continue to seal. Flushing the radiator after the process is complete would not be necessary. Simply draining and refilling the system would be fine.
Thank you!
-BDP
I have a 03 Mitsubishi Eclipse that started overheating 2 days ago. There is a rust color to the antifreeze mixture. Besides the deep clean do I need to do anything else? Would you recommend replacing the thermostat too? And I’m not sure where the engine block drain plug is so that may be out of the question for me. Will just draining from the radiator be enough?
Also someone told me that to do a flush correctly you have to use a pressurized hose like at a shop. Is this true or can you just use a regular water hose?
RJ-
Thank you for asking about your Mitsubishi Eclipse. Based on your description, a deep cleaning would be recommended. Depending on the mileage, it may not be a bad idea to replace the thermostat at this point. Draining from the radiator would be sufficient, as you would be draining multiple times to ensure nothing but clear water is coming out when you are done.
Hope this helps!
-BDP
2007 chrysler 300, 3.5 eng. The thermostat and gasket are molded together, wanting to. Flush and seal system, also the top radiator hose is half way down the radiator. And attached to eng block on side of eng where the thermos is located what’s the steps on a un natural set up as this?
Ray-
Thank you for asking about your Chrysler 300. The best way to get around the thermostat housing is by taking the thermostat and modifying it so that the middle piece does not close; you may remove this piece or gut the middle of the thermostat. By doing so you will create a free flow and still be able to have the full housing installed. The thermostat should remain “open” while BlueDevil circulates through the system. Once the BlueDevil procedure is complete you will need to replace the thermostat.
The product needs to be added to the system directly, while the engine is cold. 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 reservoir. It may be added into the hose or the opening on the radiator. Once BlueDevil has been added, reconnect the hose and start the idle from that point.
Thank you!
-BDP
I’ve got an Oldsmobile Series 66, 1942, and it’s been running very hot – it quickly pegs out at the max thermostat setting. I put Blue Devil in it and let it idle for at least a half hour if not forty five minutes and I haven’t seen any reduction in temperature yet. I don’t mind letting it go for a while but I’m worried about damaging the car if it runs hot for too long.
Andrew-
Thank you for asking about your Oldsmobile. You are correct, you would definitely want to shut the vehicle off before it looked like it was going to overheat. For an extended cleaning, you are able to leave the flush in and drive in increments up to around 4-6 hours. It’s possible that the vehicle is running hot for a different reason, meaning that a clog or debris in the system isn’t the cause of it running hot. If that is the case, try checking the thermostat to make sure it is opening at the proper temperature. This could also be the cause for the vehicle running hot.
Hope this helps!
-BDP
I’m flushing my cooling system on my 1958 ford. I know it’s not necessary to remove the thermostat but would this product work better if I did?
Thanks
Jason-
Thank you for asking about your Ford. Removing the thermostat would not help the flush work any better, however, it would create a free-flowing system, so it could help in a situation where the vehicle is starting to overheat.
Thank you!
-BDP
What happens if it drops below 32 degrees
Jeff-
BlueDevil Radiator Flush does not contain any antifreeze properties and with the mixture of water and flush in the system, would freeze in temperatures of 32 degrees and below.
Thank you!
-BDP
Is there such a thing as a coolant system cleaner that doesnt need to be flushed/drained?
Ray-
No, any kind of Radiator Flush or Cooling System Flush would be drained prior to the system being refilled with coolant.
Thank you!
-BDP
Hello – I don’t see a way to drain the block, so there will be a residual of the cleaner left in the block when the antifreeze is added. Is that OKAY??
Brad-
It would be fine if there are still trace amounts of the BlueDevil Radiator Flush in the system. Keep in mind that after running the engine with the flush and water mixture, you would drain the radiator, and then repeat the same process with just plain, clean water. Once you do the second drain, you would be fine to fill the system with your regular 50/50 mix.
Thank you!
-BDP
Will cleaning the radiator water cause water leaks or burst hoses in the engine? because all the rust and dirt will be gone. Will the cylinder head gasket burn? Is it necessary to replace the hose and radiator after cleaning?
Taner-
Flushing the radiator/cleaning the cooling system would not cause a leak to occur, unless grime, rust, dirt/debris, jellied antifreeze, etc. were plugging up a leak. It is not typically necessary to replace the radiator hose and radiator after flushing.
Thank you!
-BDP
What to do if I accidentally added some in the reservoir and now the car won’t start? Replace thermostat or water pump? Please help
Jonathan-
I assume you are rererring to adding the BlueDevil Head Gasket Sealer into the coolant reservoir? Unfortunately, that wouldn’t have any influence on the engine’s ability to turn over/crank. 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!
-BDP