Reviews

LAST UPDATED: August 15, 2019

Best Radiator Stop Leaks: Protect Your Engine and Keep Your Car Running Smoothly

Cool down your engine and fix any leaks with these radiator stop leaks

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  • Product Network

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    12 Reviews

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PUBLISHED ON August 15, 2019

There are several things you can do to make sure your vehicle is performing at its best. However, there may be times when you’ll find fluid leaks that can be a time-consuming, not to mention expensive, process to repair. This is especially true for any radiator leak, but fixing it doesn’t have to be difficult. The best radiator sealer will keep the fluid in the radiator, keeping you on the road longer. Here are the top-rated radiator stop leaks to consider the next time you need one.

  • Best Overall
    K-Seal Multi Purpose One Step Permanent Coolant Leak Repair
    Summary
    Summary
    It acts as a tight sealer for your cooling system. It is simple to use and can be applied instantly to your radiator. It’s capable of being added to both hot and cold engines.
    Pros
    Pros
    The sealant mixes with all types of antifreeze and can be left in the cooling system or flushed out if needed.
    Cons
    Cons
    K-Seal guarantees a permanent seal, but some consumers say they experienced leaking again a few weeks or months after application. Clogging can be another downside, and it is a bit on the pricier side.
  • Best Overall
    K-Seal Multi Purpose One Step Permanent Coolant Leak Repair
  • Best Value
    Bar’s Leaks Liquid Aluminum Stop Leak
    Summary
    Summary
    The compound works great at sealing leaks but also conditions the engine with liquid aluminum. It is also fitted with an Xtreme Cool formula that stops overheating and reduces the water temperature in the radiator.
    Pros
    Pros
    It easily seals leaks in plastic, aluminum, and metal radiators, heater cores, gaskets, and freeze plugs. This stop leak can be added to the cooling system without having to flush out the antifreeze.
    Cons
    Cons
    You will have to wait up to 20 minutes with the engine idling to ensure all the cracks are properly sealed. Plus, you may have to buy in bulk to get more efficient results.
  • Best Value
    Bar’s Leaks Liquid Aluminum Stop Leak
  • Honorable Mention
    ATP AT-205 Re-Seal Stops Leak
    Summary
    Summary
    A fast-acting and efficient radiator stop leak fluid. The materials are not harmful to internal bearings or components and work best on rubber seals and gaskets. Its plasticizer formula also works to restore worn or dried-out seals.
    Pros
    Pros
    It works on gasoline or diesel engines and can be added to the transmission, power steering system, and differential system as well.
    Cons
    Cons
    It might only slow down certain leaks and not permanently seal them. Also, if you have plastic, aluminum, or metal seals, it won’t work as well on them as it does on rubber.
  • Honorable Mention
    ATP AT-205 Re-Seal Stops Leak

    There are several things you can do to make sure your vehicle is performing at its best. However, there may be times when you’ll find fluid leaks that can be a time-consuming, not to mention expensive, process to repair. This is especially true for any radiator leak, but fixing it doesn’t have to be difficult. The best radiator sealer will keep the fluid in the radiator, keeping you on the road longer. Here are the top-rated radiator stop leaks to consider the next time you need one.

    Best Radiator Stop Leak Reviews & Recommendations 2020

    Best Overall

    This K-Seal leak repair provides a tight seal to your cooling system quickly and efficiently. One of the best features is that it is simple to use and can be applied instantly to your coolant system. It’s capable of being added to either a hot or cold engine, saving your time. However, use extreme caution when mixing the solution with a hot engine to avoid hurting yourself.


    Another benefit of K-Seal’s leak repair is it mixes with all types of antifreeze, so you need not worry about buying a specific brand for your car. It also can be left in the cooling system or flushed out if needed. K-Seal’s formula is designed to target holes and cracks then permanently seal them without damaging your engine.


    While this may be an excellent radiator fluid stop leak, there are a few drawbacks you should be aware of. K-Seal does guarantee a permanent seal, but many consumers report they experienced some leaking again a few weeks or months after application. This could be due to the size of the crack, but it should still block small holes without issue. Another problem is it tends to clog easily and is a bit on the pricier side.

    Best Value

    Bar’s Leak is well known for its stop leak products, and among the best is its Liquid Aluminum Stop Leak. The compound making up the fluid works great at sealing leaks, and it also conditions the engine with the use of what Bar’s Leaks call Liquid Aluminum. That’s just stepping one. Step two is known as the Xtreme Cool formula. This solution stops overheating and reduces the temperature of the water in the radiator.


    Another great feature is how durable and effective this stop leak is. It easily seals leaks in plastic, aluminum, and metal radiators, heater cores, gaskets, and freeze plugs. One other benefit is this stop leak can be added to the cooling system without having to flush out the antifreeze. It can also be used with all types of coolant, including yellow, orange, pink, red, blue, and green silicate-based and non-silicate-based antifreeze.


    While the price is a bonus, you may have to buy in bulk to get more efficient results. Another downside is you will have to wait up to 20 minutes with the engine idling to ensure all the cracks are properly sealed. However, as with all of the products mentioned here, it is not a permanent solution and your vehicle will need to be treated again or taken to a mechanic.

    Honorable Mention

    ATP is a well-known name in the world of automobiles, and it makes a fast-acting and efficient brand of radiator stop leak fluid. The materials are not harmful to internal bearings or components and work best on rubber seals and gaskets. Its plasticizer formula also works to restore worn or dried-out seals.


    A benefit of ATP’s formula is it works well no matter what engine your vehicle has. Whether it’s powered by gasoline or diesel fuel, the stop leak will seal cracks and holes in either. Another plus is the fluid can be added to the transmission, power steering system, and differential system without issue. 


    While it’s a great product for filling smaller leaks without a problem, larger leaks will require more fluid. You may also find the product might only slow down certain leaks and not permanently seal them. Also, if you have plastic, aluminum, or metal seals, it won’t work as well on them as it does on rubber.

    Honorable Mention

    Seal the leaks in your radiator with this concentrated formula. It works to seal small leaks in your radiator or heater core. Bar’s Leaks manufactures this product in the United States. One bottle can treat up to 4 gallons. This formula will address drips and leaks that occur from regular wear and tear or aging of your system. 


    This concentrate works with all types and colors of antifreeze coolant and/or water. This makes it versatile and easier to use. The concentrated formula means you only need one bottle for a regular-sized cooling system. It will work with most 6-, 8-, and 10-cylinder engines. For 4-cylinder engines, you only need half a bottle. 


    Unfortunately, this concentrate isn’t effective at sealing larger leaks or leaks that are located in the seams, bolts, or other areas of the system. It also won’t protect against overheating.

    Honorable Mention

    This product may be called GUNK, but don't let that fool you. This effective product comes from a family-owned company based in Charlotte, North Carolina. For more than 75 years, the company has produced high-quality automotive products. This aluminum formula stops leaks in your cooling system. Once applied, it will also work to prevent future leaks from happening. 


    This formulation contains a rust inhibitor to help preserve and prolong the life of your cooling system. It also begins to work immediately upon application, which is significantly faster than other products on the market. The best part about this product is that there’s no need to flush or drain the system before you apply it. 


    Unfortunately, the package for the product is smaller than other options on the market. This means that you’ll need to buy more if you have several leaks or vehicles that you are working on. You also need to check the cleanliness of your system; it needs to be clean so that you can skip draining and flushing.

    Honorable Mention

    This radiator sealant from AlumAseal is one of the original sealant products on the market. You pour the powder into your cooling system and then wait for the formula to go to work. It’s compatible with all types of antifreeze. 


    When you use this powder, you not only seal up the current leaks, but you also create a protective barrier that will prevent future leaks and rust. It will also lubricate your water pump to further preserve and extend the life of your cooling system. 


    Unfortunately, this powder is only effective at sealing small leaks or pin-sized holes. You also need to be careful, as it has clogged some vehicles’ cooling systems. The powder may not completely mix into the liquid to flow through the entire system, which can cause overheating.

    Honorable Mention

    This patented formula will work quickly to stop leaks that your cooling system has in the radiator, heater core, or water pump. The formula is enhanced with corrosion inhibitors to prevent future corrosion and pitting. This means fewer leaks in the future. 


    This product uses a unique formula that contains both natural and synthetic components. It’s effective at sealing leaks that are .020 to .5 inches in size. This means it can seal large leaks without interfering with the overall flow of coolant through your radiator. 


    Unfortunately, its claims of effectiveness might be a bit overstated. You may struggle to seal up holes on the large end of the measurement claim. If it does seal your leak, it may not last, and you’ll find your radiator leaking again.

    Honorable Mention

    This is one of the most trusted names in radiator stop leak products. It's a specially formulated and finely-ground compound. It’s non-toxic and works well in both professional mechanic shops and DIY applications. There are corrosion inhibitors included in the formula to prevent future rust. 


    The smaller grind of the powder particles means that it will mix into your cooling system fluid better and get into smaller crevices and leaks. This makes it more effective at sealing the smallest of leaks. The formulation works quickly and will save you money. 


    Unfortunately, the powder may also clog your radiator once you’ve poured it in. This could be a result of using too much powder. This can easily happen if you find that the first vial didn’t effectively seal your leak. There is a fine balance between the powder being totally ineffective and clogging your radiator.

    Honorable Mention

    Liqui Moly's stop leak is for use in passenger vehicles, commercial vehicles, buses, and more. It seals hair cracks as well as tiny leaks caused by impacts and porous soldering points. The product is compatible with antifreeze and coolant water refiners and works on aluminum radiators and cooling water and heating systems, both with and without water filters.


    Liqui Moly is made in Germany and works particularly well on European vehicles. It functions as it promises, and it stops leaks as advertised. It's a great product if you need a quick and temporary coolant system leak repair. It isn't uncommon for the product to seal a leak for several months.


    There are not many downsides to this product. It does not solve every type of leak. You may need more than one bottle to stop up larger holes, and it's not a permanent fix.

    Why Trust Us


    All of our reviews are based on market research, expert input, or practical experience with most products we include. This way, we offer genuine, accurate guides to help you find the best picks.

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    Benefits of Radiator Stop Leak

    • Prevent a breakdown. Driving with a radiator leak is incredibly harmful to your vehicle. Any major loss of radiator fluid will likely cause your car to break down, leaving you stranded on the side of the road. The radiator works by cooling down the vehicle’s engine with the use of liquid coolant. The hotter the engine gets, the higher the chance it will overheat, causing a breakdown.
    • Keep yourself safe. Making sure your car is topped off with radiator stop leak fluid means you’ll be safer on the road. There’s little to no risk of the radiator overheating on you mid-drive, forcing you to pull over or stop in the middle of traffic.
    • Improve performance. Checking to make sure the radiator stop leak is constantly getting fluid will help keep the car running properly. Over time, a leak will wear down your car’s power and could damage other parts of the vehicle. Making sure the reservoir where the fluid is kept isn’t leaking will keep your car running smoothly.
    • Save money. Stopping a radiator fluid leak will ultimately save you money. Catching it before it gets worse means you won’t have to take the car to the shop for a full radiator overhaul, and doing nothing about it may lead to other problems and leave you with a hefty cost to your radiator or other parts of the car.
    • Protect seals. Hardened or dried seals cause most oil leaks. Oil leak additives work by revitalizing the main seal and head gaskets to return to their original size and flexibility. This reduces the amount of oil that is capable of seeping through.

    Types of Radiator Stop Leaks

    Tablets

    While not the most common type of radiator stop leak, you can find the product in a tablet form. It works by dissolving in the fluid to form tiny particles. These particles flow to leak areas to fill the gaps and holes causing the seepage. Then when the temperature reaches a certain degree, the particles burn up to seal cracks.

    Liquid

    Liquid forms of stop sealant are much more common and have a lower viscosity. This makes them move more smoothly through the radiator fluid while also reducing friction. These tend to be made up of additives that help corrode rust and are thicker to fill leaks and reduce dirt and grime.

    Top Brands

    Bar’s Leaks

    First founded in California in 1947 by Fred Barton, Bar’s Leaks now calls Holly, Mich., it's home. It makes high-quality stop-leak products for vehicles, including the Bar’s Leaks Liquid Aluminum Stop Leak.

    Prestone

    Headquartered in Chicago, Ill., Prestone makes antifreeze, coolants, brake fluids, and power steering products. It’s been in business since 1927 and sells the Prestone Radiator Sealer Stop.

    ATP

    Another recognizable name in automobile parts is ATP. The company started at a Chicago plant in 1955 and it sells transmission parts, filter kits, repair kits, cables, flywheel and ring gears, cabin air filters, chemicals, and much more for your vehicle. The ATP AT-205 Re-Seal Stops Leak is one of its most purchased items.

    Radiator Stop Leak Pricing

    • $5-$35: With radiator stop leak fluid, you mainly pay for the size and capacity of the container. Within this price range, you’ll find anything around 12 ounces and below.
    • $35 and up: This price range has larger bottles and containers that offer more solution for more applications. It may be best to buy it in bulk to make sure you have extra just in case you run out when you need it most.
    Yellow car with steam pouring from the hood.
    Gettyimages

    You will want to make sure the radiator stop fluid you buy works with your antifreeze. Check the labeling to make sure it is compatible with all types to avoid damaging your vehicle.

    Key Features

    Additives

    Additives in radiator stop leak fluids work to remove debris, neutralize acidity, and fill leaks. However, the majority are not a permanent solution to fixing a leak in your radiator but are only a temporary fix. Over time, a leak can start again, and you’ll have to add the fluid once more.

    Compatibility 

    Before choosing the best radiator stop leak, you need to read the label carefully. Not all anti-leak fluids will work for every car. Many are specifically designed for certain models like Honda or Ford or engine types such as diesel or gasoline. Make sure to double-check the fluid before buying it to make sure you don’t pour the wrong stop leak into your car.

    Other Considerations

    • Clogs: Some radiator stop leaks can clog up, while others will flow more freely and provide less friction. To make sure you don’t run the risk of clogs, read the label to see if the particular compound will work for your particular vehicle’s radiator.
    • Chemicals: Stop leaks come with a wide variety of chemical compounds and materials. This all depends on the manufacturer, so you’ll need to check the substances found inside the bottle before using it to see if they will cause issues with the antifreeze or damage the engine.
    • Frequency of Use: It is important to consider how frequently you need to use it and what effect it will have on your vehicle in the long run. Keep in mind that fluid can be used multiple times before running out.

    Best Radiator Stop Leak Reviews & Recommendations 2020

    Best Overall

    This K-Seal leak repair provides a tight seal to your cooling system quickly and efficiently. One of the best features is that it is simple to use and can be applied instantly to your coolant system. It’s capable of being added to either a hot or cold engine, saving your time. However, use extreme caution when mixing the solution with a hot engine to avoid hurting yourself.


    Another benefit of K-Seal’s leak repair is it mixes with all types of antifreeze, so you need not worry about buying a specific brand for your car. It also can be left in the cooling system or flushed out if needed. K-Seal’s formula is designed to target holes and cracks then permanently seal them without damaging your engine.


    While this may be an excellent radiator fluid stop leak, there are a few drawbacks you should be aware of. K-Seal does guarantee a permanent seal, but many consumers report they experienced some leaking again a few weeks or months after application. This could be due to the size of the crack, but it should still block small holes without issue. Another problem is it tends to clog easily and is a bit on the pricier side.

    Best Value

    Bar’s Leak is well known for its stop leak products, and among the best is its Liquid Aluminum Stop Leak. The compound making up the fluid works great at sealing leaks, and it also conditions the engine with the use of what Bar’s Leaks call Liquid Aluminum. That’s just stepping one. Step two is known as the Xtreme Cool formula. This solution stops overheating and reduces the temperature of the water in the radiator.


    Another great feature is how durable and effective this stop leak is. It easily seals leaks in plastic, aluminum, and metal radiators, heater cores, gaskets, and freeze plugs. One other benefit is this stop leak can be added to the cooling system without having to flush out the antifreeze. It can also be used with all types of coolant, including yellow, orange, pink, red, blue, and green silicate-based and non-silicate-based antifreeze.


    While the price is a bonus, you may have to buy in bulk to get more efficient results. Another downside is you will have to wait up to 20 minutes with the engine idling to ensure all the cracks are properly sealed. However, as with all of the products mentioned here, it is not a permanent solution and your vehicle will need to be treated again or taken to a mechanic.

    Honorable Mention

    ATP is a well-known name in the world of automobiles, and it makes a fast-acting and efficient brand of radiator stop leak fluid. The materials are not harmful to internal bearings or components and work best on rubber seals and gaskets. Its plasticizer formula also works to restore worn or dried-out seals.


    A benefit of ATP’s formula is it works well no matter what engine your vehicle has. Whether it’s powered by gasoline or diesel fuel, the stop leak will seal cracks and holes in either. Another plus is the fluid can be added to the transmission, power steering system, and differential system without issue. 


    While it’s a great product for filling smaller leaks without a problem, larger leaks will require more fluid. You may also find the product might only slow down certain leaks and not permanently seal them. Also, if you have plastic, aluminum, or metal seals, it won’t work as well on them as it does on rubber.

    Honorable Mention

    Seal the leaks in your radiator with this concentrated formula. It works to seal small leaks in your radiator or heater core. Bar’s Leaks manufactures this product in the United States. One bottle can treat up to 4 gallons. This formula will address drips and leaks that occur from regular wear and tear or aging of your system. 


    This concentrate works with all types and colors of antifreeze coolant and/or water. This makes it versatile and easier to use. The concentrated formula means you only need one bottle for a regular-sized cooling system. It will work with most 6-, 8-, and 10-cylinder engines. For 4-cylinder engines, you only need half a bottle. 


    Unfortunately, this concentrate isn’t effective at sealing larger leaks or leaks that are located in the seams, bolts, or other areas of the system. It also won’t protect against overheating.

    Honorable Mention

    This product may be called GUNK, but don't let that fool you. This effective product comes from a family-owned company based in Charlotte, North Carolina. For more than 75 years, the company has produced high-quality automotive products. This aluminum formula stops leaks in your cooling system. Once applied, it will also work to prevent future leaks from happening. 


    This formulation contains a rust inhibitor to help preserve and prolong the life of your cooling system. It also begins to work immediately upon application, which is significantly faster than other products on the market. The best part about this product is that there’s no need to flush or drain the system before you apply it. 


    Unfortunately, the package for the product is smaller than other options on the market. This means that you’ll need to buy more if you have several leaks or vehicles that you are working on. You also need to check the cleanliness of your system; it needs to be clean so that you can skip draining and flushing.

    Honorable Mention

    This radiator sealant from AlumAseal is one of the original sealant products on the market. You pour the powder into your cooling system and then wait for the formula to go to work. It’s compatible with all types of antifreeze. 


    When you use this powder, you not only seal up the current leaks, but you also create a protective barrier that will prevent future leaks and rust. It will also lubricate your water pump to further preserve and extend the life of your cooling system. 


    Unfortunately, this powder is only effective at sealing small leaks or pin-sized holes. You also need to be careful, as it has clogged some vehicles’ cooling systems. The powder may not completely mix into the liquid to flow through the entire system, which can cause overheating.

    Honorable Mention

    This patented formula will work quickly to stop leaks that your cooling system has in the radiator, heater core, or water pump. The formula is enhanced with corrosion inhibitors to prevent future corrosion and pitting. This means fewer leaks in the future. 


    This product uses a unique formula that contains both natural and synthetic components. It’s effective at sealing leaks that are .020 to .5 inches in size. This means it can seal large leaks without interfering with the overall flow of coolant through your radiator. 


    Unfortunately, its claims of effectiveness might be a bit overstated. You may struggle to seal up holes on the large end of the measurement claim. If it does seal your leak, it may not last, and you’ll find your radiator leaking again.

    Honorable Mention

    This is one of the most trusted names in radiator stop leak products. It's a specially formulated and finely-ground compound. It’s non-toxic and works well in both professional mechanic shops and DIY applications. There are corrosion inhibitors included in the formula to prevent future rust. 


    The smaller grind of the powder particles means that it will mix into your cooling system fluid better and get into smaller crevices and leaks. This makes it more effective at sealing the smallest of leaks. The formulation works quickly and will save you money. 


    Unfortunately, the powder may also clog your radiator once you’ve poured it in. This could be a result of using too much powder. This can easily happen if you find that the first vial didn’t effectively seal your leak. There is a fine balance between the powder being totally ineffective and clogging your radiator.

    Honorable Mention

    Liqui Moly's stop leak is for use in passenger vehicles, commercial vehicles, buses, and more. It seals hair cracks as well as tiny leaks caused by impacts and porous soldering points. The product is compatible with antifreeze and coolant water refiners and works on aluminum radiators and cooling water and heating systems, both with and without water filters.


    Liqui Moly is made in Germany and works particularly well on European vehicles. It functions as it promises, and it stops leaks as advertised. It's a great product if you need a quick and temporary coolant system leak repair. It isn't uncommon for the product to seal a leak for several months.


    There are not many downsides to this product. It does not solve every type of leak. You may need more than one bottle to stop up larger holes, and it's not a permanent fix.

    Tips

    • Keep in mind that many oil additives can include harmful chemicals. These can have a long-lasting effect on your vehicle's engine. Keep an eye out for products that are certified by the EPA.
    • Wear gloves, masks, and protective eyewear while using a stop leak. If it touches your skin, it may be difficult to clean off. Getting it in your eyes could lead to irritation or worse symptoms.
    • To see if you’ve successfully stopped a leak, leave a piece of cardboard under the car where the fluid usually leaks. After filling the reservoir with stop leak, drive the car around for a bit, and then park it over the cardboard. Check the cardboard to see if any leakage took place.

    FAQs

    Q: How long until I see results from a stop leak product?

    A: This can be a difficult question to answer, and it all depends on the type and manufacturer of the stop leak. Many need at least 10 to 20 minutes to fully take effect, while others need a few hours. The size of the crack or hole also matters; the larger the crack, the more time it will take to fill it properly.

    Q: Is a stop leak a permanent fix?

    A: While stop leaks may seem like a permanent solution to your problem, they only last a short amount of time. To truly fix a leak for good, you will need to take your car to a mechanic to get a better understanding of the leak.

    Q: Do I need to drain the cooling system after using stop leak?

    A: Generally, most radiator stop leak fluids do not require you to drain the system after applying the solution. However, read the labeling to see what the manufacturer recommends.

    Q: What should I do if the sealant doesn’t work?

    A: Remember, not all radiator stop leaks are permanent. If you don’t see an improvement after applying the fluid, you may need to take it to a mechanic for a more in-depth diagnosis.

    Final Thoughts

    If you want a reliable and efficient radiator sealant, consider the K-Seal Multi Purpose One Step Permanent Coolant Leak Repair. You can save a bit of money and still get a great stop leak fluid with Bar’s Leaks Liquid Aluminum Stop Leak.