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Top 6 Best Radiator Stop Leaks Recommended In 2021 Reviews

Since a radiator plays a huge part in serving the vehicle, it is necessary to keep this component healthy and leak-proof. Due to consistent use, some cracks or holes develop on its surface. Consequently, issues like leakage of the coolant and overheating of the system occur.

If not treated immediately, such issues pose a risk to the life and performance of the vehicle. In order to prevent this from happening, we need to seal all the slits and cracks. It is very convenient to do so with the help of some best radiator stop leaks reviewed in this article.

More on this later…

The article also includes some shopping tips helpful for the purchase of radiator sealants. Without further delay, let’s get started.

Best Radiator Stop Leak

Best Radiator Stop Leaks Comparison Table

ProductsCompatibility with CoolantLeak SizeRating
Compatibility with Coolant
All types of antifreeze
Leak Size
Small to medium
5 out of 5 stars (5 / 5)
Compatibility with Coolant
ATF, synthetic, gear and hydraulic oil
Leak Size
Small to large
4.5 out of 5 stars (4.5 / 5)
Compatibility with Coolant
All types of antifreeze
Leak Size
Small to medium
4.3 out of 5 stars (4.3 / 5)
Compatibility with Coolant
All types of antifreeze
Leak Size
Small to medium
4.5 out of 5 stars (4.5 / 5)
Compatibility with Coolant
All types of antifreeze
Leak Size
Small to medium
4.5 out of 5 stars (4.5 / 5)
Compatibility with Coolant
Gasoline and diesel engine and all types of coolants
Leak Size
Small to large
4.3 out of 5 stars (4.3 / 5)

Top 6 Best Radiator Stop Leaks On The Market In 2021 Reviews

1 K-SEAL Coolant Leak Repair, ST5501

The most important thing to remember, the composition of this radiator stop leak mainly comprises ceramic microfibers and copper particles, mixed well in suitable propositions. The best part about these additives is they are absolutely safe for the vehicle’s engine and all other bearings.

Apart from that, the particle size is conducive to filling the gap of about 0.635 mm. On the whole, there is no possibility of blockage of tubes and other passageways.

Still not convinced?

The barrier it creates is sufficiently durable to stay intact against the pressure of exhaust gases, usually released by the combustion compartment. This property makes this leak-preventing solvent appropriate for the conditioning and repair of several assemblies. These assemblies include the head gasket, heater core, freeze plugs, water pump casing, cylinder heads, and engine.

Using this liquid is very easy and can be done without professional help. Most interestingly, it does not require flushing of the radiator prior to the use.

Yes, you read that right.

All you have to do is shake the jar thoroughly and pour in the liquid. The stop leak will, subsequently, get mixed with the coolant itself and will start working upon approaching the desired location. That’s how easy it is to repair the broken cracks with this product.

Besides, K-seal coolant leak repair is free from petroleum distillates. Also, it contains no substance that could be hazardous for the user or vehicle in any case. After going through analytical testing, it is found to meet the safety standards of ASTM D3147. Hence, you can use it without any worries.

K-SEAL Coolant Leak Repair, ST5501
Our rating:5 out of 5 stars (5 / 5)


  • Made from anti-blocking ingredients.
  • Seals holes strongly.
  • Very affordable.
  • No harmful effects on the vehicle.
  • Works without needing to empty the radiator.


  • The seal does not last forever.

2 ATP AT-205 Re-Seal Stop Leak

This is one of the best plastic and rubber radiator stop leaks. If a rubber or plastic radiator is embedded in your vehicle, then this product will impress you with its long-lasting results.

What’s new?

All the ingredients involved in making this leak stopper improve the quality of rubber and plastic materials, hence contribute to their existing flexibility. Not only the cracks are sealed, but the radiator also undergoes a thorough repair. In other words, it increases the radiator’s lifespan besides sealing the holes.

That’s not all!

It tends to blend well in the composition of the coolant, be it ATF, synthetic oil, gear oil, or hydraulic oil. Therefore, a user does not have to get into frustrating and messy procedures for flushing the coolants. However, shaking the bottle and mixing the ingredients is recommended prior to every use.

Don’t worry; the vehicle is safe!

As it includes no harmful material, the internal components of a vehicle are out of danger. Thus, you can make the most of this best radiator stop leak for sealing the holes in the engine, hydraulic system, power steering system, and differential system.

You will receive eight ounces of liquid in a single bottle, which is enough for a six-quart capacity radiator. Moreover, it is quite skin-friendly and easy-to-use. Forget about flushing the coolants and grab ATP AT-205 Re-Seal stop leak to experience an ultra-efficient performance with your old radiator.

ATP AT-205 Re-Seal Stop Leak
Our rating:4.5 out of 5 stars (4.5 / 5)


  • Good for rubber and plastic radiators.
  • Goes with all anti-freezes.
  • Mixes completely and instantly.
  • Free from petroleum distillates.


  • Not a good option for blown-out slits.

3 Bar’s Leaks 1186 Liquid Aluminum Stop Leak

Next in line is the best aluminum radiator stop leak. It is manufactured by a renowned and market-leading brand that has been striving to relieve vehicle owners through their innovative automobile must-haves for seventy years. With that being said, we were compelled to include this product to our list.

The reason being the great sealing characteristics, this stop leak promises to do the task of repairing small and medium-sized holes and cracks and ensure long-term services.

It all boils down to this…

The anti-freeze material is no more a point of restriction as long as you have this leak sealant. It has the ability to homogenize in every type of coolant. Furthermore, if you employ water as a coolant, then this is the best radiator stop leak because it performs as amazingly with the universal solvent as it does with any other antifreeze.

Upon amalgamating with the coolant, it proceeds towards the leak opening and comes into action in no more than 20 minutes. Therefore, it is not only effective but also super-fast.

Liquid aluminum is the basic element included in the formula of this radiator sealant. That’s why it attaches to the cracked parts firmly and inhibits the transfer of fluid, thereby saving fuel and money. On top of that, the shake-and-pour formula enables you to repair moderately-sized holes by yourself.

Besides fixing the cracks, it also readily tunes the system, which makes it stand out in the crowd. All of this makes it the best radiator stop leak for the price point.

Bar’s Leaks 1186 Liquid Aluminum Stop Leak
Our rating:4.3 out of 5 stars (4.3 / 5)


  • It can also be used for heater core and tanks.
  • Reliable and environment-friendly composition.
  • Quick results.
  • No problem if the coolant is water.


  • Inefficient for large holes and water pump cracks.

4 AlumAseal ASD24/2-24PK Radiator Sealer Tube Dispenser

Here’s another radiator sealant that has something unique in it. It comes in the form of well-crushed powder, which causes no sticky mess, unlike a mess that occurs when using liquids.

A single package consists of 24 sachet-like packets, each containing enough powder for a 20-quart capacity. Also, it is available at reasonable costs. Thus, you can give it a try and decide on the credibility of this product by yourself.

And you know what…

Being in the solid powder state, it dissolves in the provided coolant as swiftly as it comes in contact with the solvent. Meanwhile, it rushes to the cracked point and seals it very smoothly, leaving the antifreeze unable to make its way out of the radiator.

Since it can dissolve with all coolants, whatever the antifreeze composition, the solution turns out to be homogenous and free of clumps. This is why the passageways are not susceptible to clogging at all and remain clear despite the frequent use of this sealant.

The types of materials that this stop leak makes the best bonds with include rubber, metal, and plastic. It shows the most wanted results in just a few minutes.

AlumAseal ASD24/2-24PK Radiator Sealer Tube Dispenser
Our rating:4.5 out of 5 stars (4.5 / 5)


  • Resists particles from blocking the unintended gaps.
  • Dissolves in all coolants.
  • Mess-free operation.
  • Conditions the cooling system.


  • Temporary performance.

5 Bar’s Leaks HDC Radiator Stop Leak Tablet

Six stop leak tablets, provided in a package, seal the gaps through an exclusive fast-action formula. For dissolving them, take some warm water, then add the resulting mixture into the coolant. As a matter of fact, the coolant can be of any type or category.

While it dissolves, you will notice the tablet particles will reduce by 15% in size. In his way, these shrank particles move to the open area we want to cover and seal it. Soon, a strong, impenetrable, and non-porous adhesive film will be built on the gap. This closure is fully resistant to catching rust, abrasion, and chemical corrosion.

If that’s not enough…

Each sealant tablet balances and maintains the pH value of the coolant, including the silicon-based ones. It also lubricates the openings it blocks to eradicate the chances of rusting.

All these advantages are ensured for metal, plastic, and aluminum radiators, connections, and hoses. Thus, those who are in search of sealants for any of these materials should buy this product and avail its benefits at the earliest.

Bar’s Leaks HDC Radiator Stop Leak Tablet
Our rating:4.5 out of 5 stars (4.5 / 5)


  • Rust- and corrosion-free sealing.
  • Controls the pH level of the coolant.
  • It requires only 20 minutes to get the vehicle ready to run.


  • Not useful for large cracks.

6 Blue Devil Radiator and Block Sealer

Obviously, cracks in a radiator may recur after some days. But the problem is that who has time to waste on mending each gap and hole now and then? Therefore, every person wants to have a permanent or at least a long-running solution. For such individuals, we have something special to introduce.

Blue Devil block sealer blocks leakage-causing holes for a very long span of time. What makes this product so practical is the composition, which includes no porous or insoluble solid particles. Resultantly, the sealer does not choke the components and also stops the fluid from leaking.

The best part…

You can use this sealant, whether you have a diesel or gasoline engine. In fact, it offers compatibility with all types of coolants, which makes it favorable and safe for most vehicles. As for the radiator materials, it has no particular criterion and easily repairs plastic, aluminum, and metal radiators.

Even though it’s quite easy to use, still you can follow the simple directions mentioned on the bottle. That being the case, you can use this sealant to get rid of radiator leakage problems and continue driving like a pro.

After passing it through numerous laboratory and practical testing, it has been declared as ASTM D1881– and ASTM D3147-compliant sealer. Owing to this fact, we can conclude it emphasizes your and vehicle’s safety, and the product’s success rate is also beyond the expectation of many.

Blue Devil Radiator and Block Sealer
Our rating:4.3 out of 5 stars (4.3 / 5)


  • Seals leak points permanently.
  • Best radiator stop leak for both gasoline and diesel rigs.
  • Contains safe-to-use additives.
  • Equally functional for metal, aluminum, and plastic radiators.
  • Backed by ASTM D1881 and ASTM D3147 standards.


  • Better to flush out the coolant.

Best Radiator Stop Leaks Buying Guide

Sealants have made our lives easier, as these include no tricky methods of use. Anybody can repair radiator leaks without taking the vehicle to a mechanic and paying a significant amount of money for just a 20-min task.

But this is only possible if we lay hands on the right product. Before choosing a sealant, we must consider some critical aspects and make sure that the sealant boasts those fundamentals. Now let’s find out what makes a sealant worth buying:

Radiator Stop Leak

  • Check the Compatibility

The tendency of a sealant to mix with the coolant or antifreeze depends on its material composition. Some sealants work with all types of coolants and engines, whereas some work for certain antifreeze. All in all, you pick the wrong or incompatible stop leak, your vehicle will be at risk and can cost you heavily.

Let’s get to the point…

Don’t forget to go through the specifications or ingredients listed on the package. Buy it if it says it is safe for all cooling systems or for the type of coolant your vehicle consumes.

  • Price Range

The market contains a plethora of radiator sealants with different qualities, lasting powers, and cost range. Even high-quality sealants belonging to reputed brands are available at affordable prices.

So, don’t go beyond your budget to purchase an effective stop leak. Rather, go for pocket-friendly products that also offer the desired benefits and meet the basic requirements.

  • Leak Size

The size of the gap your radiator incurs also matters a lot. If it is very small, it would be fine to buy any sealant. However, you must be careful in the purchase if the leak size is considerably large or has undergone wear-out or severe damage.

If a stop leak claims to work for minor holes only, it means the sealing will break on large cracks. Keeping this in mind, look for extraordinary products to mend large gaps efficiently.

  • Location and Material of Leak Area

It’s recommended to consider the sealing potential of the sealant. Some stop leaks turn into sturdy physical constrictions that remain unaffected. Surprisingly, factors like prolonged use, temperature changes, the pressure of the combustion chamber, pH imbalance, and weather harshness also fail to ruin the seal. Such sealants are preferred for hoses, heater cores, radiators, tanks, and head gaskets.

You must select a sealant that works best for the construction material of the radiator. An aluminum sealer may not be appropriate for rubber cracks. Likewise, choosing plastic radiator stop leaks for metal radiators may also disappoint you. In a nutshell, verify the functionality of the sealant for the particular radiator.

  • Ease of Use

Stop leaks are manufactured in a liquid state, solid powder, and tablet form. Hence, select the type of product that suits your comfort level. Tablets are mess-free formula and are very handy and safe to use. Just prepare a mixture of tablets in lukewarm water and pour it into the radiator.

Liquid sealers don’t need any sort of preparation. It is to be noted, shaking the bottle or container is necessary to homogenize everything well. Powdered stop leaks are also convenient to handle and mix.


Sealers give us an opportunity to fix radiator leakage issues in less than an hour and on the go. After applying them to cracks and holes, we can forget about the leakage, at least for a month or so. To summarize, the products reviewed above are the best radiator stop leaks. You can count on them to repair and condition the radiator according to your vehicle’s demands.

Time to announce the winner

Although all the products are equally resourceful and advantageous,

K-Seal Coolant Leak Repair ST5501

seems to steal the show and very clearly beat its competitors.

Here is why…

This ASTM D3147-qualified sealant is composed of human-safe and effective ingredients. For this reason, it extends its services for components like radiators, head gaskets, freeze plugs, cylinder heads, and engines.

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