[Top 10] Best Radiator Stop Leak on The Market

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Best Radiator Stop Leak on The Market

Like most parts of a car, the radiator takes its fair share of pounding every day. As long as antifreeze flows through the engine there’s definitely going to be heat output. So your car’s cooling system needs to be in its best shape to avoid expensive damages.

That’s why it’s definitely not a good sign when you find a pool of colored liquid beneath your car. It means an expensive repair or replacement is afoot. Thankfully, radiator stop leaks are available to help you avoid such an issue.

Choosing a radiator stop leak is the hard part which is why you’re here reading this guide. Trying to avoid the troubles of a flooded market. The same market where inferior goods are so easy to come by.

Read on as we’ve prepared for you the necessary information you need in making the best choice in terms of quality and price. We’ve prepared 10 reviews of the best radiator stop leaks you’ll find in the market today!

10 Best Radiator Stop Leak on The Market

Last update on 2021-12-05 at 04:18 / Affiliate links / Images from Amazon Product Advertising API

1. K-SEAL Coolant Stop Leak Repair – Best Radiator Stop Leak

k-seal is a trusted brand known for providing top-notch additives. This leak repair bottle is no different, as it contains a special blend of ingredients such as ceramic fibers and Copper particles. 

The particles were designed precisely to repair holes with a size of 0.025 inches. They were also designed precautionarily to be small enough not to cause clogs and in the cooling system. And they mix well with anti-freeze.

This multi-purpose sealant guarantees permanent seals in radiator leaks, water-cooled engines, and water pumps. Another great feature is its durable seal which can withstand high pressure even from the engine’s combustion chamber.

If it’s the speed that is a big factor to you, k-seal provides faster sealing in which in most cases works almost instantly. If not, it’ll take between 10-20 minutes at most. The product is easy to use as it’s in the form of fluid contained in a bottle. All you need to do is shake, twist open the cap and dispense the sealant carefully into the radiator.


  • Seals instantlyI
  • t’s multi-purpose
  • Extremely durable seal
  • Permanent seal
  • Mixes well with antifreeze 


  • An incompatible radiator will be clogged

2. ATP AT-205 Re-Seal Stops Leaks – Best Plastic Radiator Stop Leak

If you’re looking to save your previous seal from breaking down, then you’ll need ATP Re-seal which helps to rejuvenate them. This is possible as the fluid acts as a plasticizer. In other words, it improves the flexibility of seals without causing over swelling or breakdown in them. This special feature makes it great for conditioning rubber in the hydraulic system.

ATP Re-seal blends easily with oil which is why it’s great for sealing leaks in other systems apart from radiators. The list includes transmission and power steering systems. Time taken to re-seal is quite long, as you need to take it out for at least a 5 hours drive.

It’s easy to use as the fluid is kept in a bottle with a long spout for easy dispensing. Also safe, with no ounce of petroleum distillate in its formula.


  • Easy to use
  • Rejuvenates rubber seals
  • Absence of petroleum distillate
  • Compatible with automotive oil


  • There could be damage in transmission
  • It mainly offers rubber seals

3. Bar’s Leaks 1186 Liquid Aluminum Stop Leak – Best Liquid Aluminum Stop Leak

Bar’s leak is another trusted popular brand that has provided vehicle user’s additives for about 100 years now. Their successful service continues with this special blend of sealant which contains effective ingredients. 

The ingredients include liquid Aluminum and a special substance known as Xtreme cool. Together, they don’t only seal leaks but also condition the system to prevent future problems like leaks in the heater core. Apart from small leaks, the bar’s sealant can also repair large leaks, credits to its liquid aluminum ingredient. 

Bar’s leak sealant is quite convenient, considering its ability to easily mix with antifreeze, as well as water. If you wish to mix with water, another bottle of liquid aluminum must be added. That’s Immediately after antifreeze has been installed. 

Another feature to consider is the time taking to seal which is almost instant. Or it would take 10-20 mins.


  • Mixes with water and antifreeze
  • It seals leaks and conditions the system
  • It can repair gasket leaks
  • Instant seal 
  • Great for large leaks


  • You might need two bottles

4. Prestone AS145 Radiator Sealer Stop Leak – Top Rated Stop Leak for Radiator

Prestone presents a stop leak that solves both the immediate and the pending issues concerning your radiator, as well as your vehicle’s entire cooling system. This is so due to their patented unique blend of both natural and synthetic ingredients. A fibrous material that can also be found is in bulletproof vests. 

The blend is made to plug holes of sizes within 0.02 – 0.50 inches. Despite its ability to seal large holes, the blend doesn’t clog the cooling system. Apart from sealing leaks, the sealant can as well condition the system to prevent pitting and corrosion which causes leaks. This makes Prestone AS145 a permanent solution.

Water pumps and heater cores are also parts of the cooling system it can seal. And it only takes a few minutes, as Prestone’s sealant works almost immediately.


  • Builds a very strong seal
  • It helps to prevent pitting and corrosion
  • It takes effect almost immediately
  • Permanent


  • Slightly expensive

5. J-B Weld DS-114 Radiator Stop Leak – Best Powdered Stop Leak

This is a favorite for DIYers due to its gentle application but tough sealing of leaks and cracks within the cooling system. Much of the credit goes to its convenient non-toxic powdery fine form.

Another reason why it’s a favorite is the affordable price tag. Which is attractive to first-timers exhausted by constant trips to the mechanic shop for every little mishap. The sealant is also a great rust inhibitor and can go great as a lubricant.

If it’s quick service you require, J-B Weld’s perm o seal works immediately as it flows through the system. There is no need to worry about clogging given it’s a finely grounded powdered stop leak. Due to that property, the sealant is very convenient to use. All that’s required is a funnel to prevent a mess. A face mask to prevent inhalation of the substance.


  • Affordable
  • Very durable
  • Non-toxic
  • It can be used as a lubricant
  • Works quickly


  • It’s not a permanent solution
  • It’s not compatible with most cooling systems

6. Bar’s Leaks 1109 Block Radiator Stop Leak – Best Liquid Copper Radiator Stop Leak

This is a liquid Copper stop leak which is great at sealing large holes. The kind of holes you’ll find in old cars, RVs, SUVs, and trucks. This sealant is best used to plug holes in radiators and intake manifolds of such vehicles. 

Bar’s leak liquid copper sealer has a unique feature which is the sealant’s compatibility with antifreeze and water. Sodium silicate (liquid glass) is the main ingredient that ensures its compatibility.

With the formula antifreeze compatible, you don’t need to flush out the coolant before applying. Or If you decide to mix the formula with water, then you’ll have to prepare another bottle of liquid copper.   

The product is quite easy to use given it’s contained in a bottle which allows easy dispensary. Its effect only takes a few minutes.


  • It’s a liquid copper stop leak that mixes with antifreeze
  • It seals quickly
  • It can plug large leaks
  • Very easy to apply 


  • Incompatible radiators might get clogged

7. Bar’s Leaks HDC Radiator Stop Leak Tablet – Best Budget Radiator Stop Leak

This tablet sealant is the most inexpensive and effective means of plugging leaks in a cooling system. Bar’s leak presents its HDC Radiator stop leak which requires a container of warm water for pre-dissolving. The sealant can also be dissolved in antifreeze. So there’s no need to flush out the coolant when applying the stop leak.

Once the sealant is applied, you should expect a durable seal that’ll hold perfectly for a long time. Apart from providing a perfect seal, bar’s leaks HDC Radiator stop leak can act as an effective lubricant in water pumps and other pipings in the cooling systems.

Due to the sealant’s special formula, it’s compatible with a wide range of radiators and engines. This means your cooling system is less likely going to be clogged. The formula also helps to reduce the presence of internal static electricity in the cooling system.


  • It’s great for a wide range of engines and radiators
  • It’s a great lubricant for water pumps and pipings
  • The risk of blockage is low
  • Decreases static electricity


  • It’s can’t handle large leaks

8. Dike Temporary Radiator Stop Leak – Best Temporary Radiator Stop Leak

Here’s another stop leak to meet your demands. It’s not so expensive but its ability to form a strong seal on small leaks is impressive. Apart from plugging leaks, Conklin dike’s sealant also conditions the cooling system to prevent further leaks into the engine. This helps to prevent the clogging of oil passages and loss of engine oil viscosity. 

The sealant requires little time to take effect. After applying, you’ll need to keep the engine running for at least 15 minutes to enable full circulation of sealant. The sealant can mix with antifreeze, so you don’t need to flush the radiator. If needed, you can as well top off the coolant.

Given the product is in the form of a fluid contained within a bottle, dispensing is easy. All you have to do is shake and pour the sealant into the radiator. Conklin’s dike’s temporary radiator stop leak works for all vehicles that make use of a cooling system.


  • It’s great for all cooling systems
  • It mixes with antifreeze
  • Takes up to 15 minutes to seal
  • Inexpensive


  • It can’t handle large leaks
  • It’s a temporary fix

9. Bar’s Leaks G12BP Powder Radiator Stop Leak – Best Versatile Radiator Stop Leak

Bar’s leaks appear once again on this round-up list with yet another powder-based sealant. Its formula consists of millions of particles great for sealing plastic, aluminum, and metal radiators. It also provides a strong seal for other parts Such as the heater cores and water pumps.

This sealant can as well be used to condition the cooling system to help inhibit corrosion and rust. It mixes well with most antifreeze, so you don’t have to worry about persistent leaks.

The powdered form of the product allows for dispensing. Especially with the aid of a funnel which helps to prevent a mess. A face mask should also be available for your safety as a user.


  • Great for small leaks
  • Helps to control internal electrolysis
  • Conditions the system to inhibit rust & corrosion
  • Mixes well with antifreeze
  • Easy to dispense
  • Works quickly
  • Affordable 


  • Temporary fix

10. Genuine GM Cooling System Seal Tablet – Best Cheap Radiator Stop Leak

If you’re looking to save some money and still gain on quality, then this is the sealant for you. Most users of this product refer to it as a low-cost miracle. Given it’s not the best but it does the job. It provides a strong and permanent seal. This is due to the sealant’s original and organic formula, which mixes well with antifreeze.

The unique feature of this sealant is that the formula is specially designed to handle minor leaks. It’s also designed to condition the system in such a way it inhibits the development of rust and corrosion in the future.

Given the product is in the form of tablets, the application is as easy as dissolving in water or antifreeze. The sealant can be used in all vehicles that have a cooling system.


  • Inexpensive
  • Develops a strong seal
  • Mixes well with antifreeze
  • Great for most vehicle’s radiator
  • Inhibits rust and corrosion
  • Non-toxic 


  • It can only handle small leaks
  • Temporary fix

The round-up above is based on the factors and information we’ve taken into account. Which we use to set up the sealants as viable options for your vehicle. Read on as you’ll get the details.

What should I look for When Buying a Radiator Stop Leak?

Size of leak

Do not neglect any sign of a leak as it could get too large for you to handle. Worst case scenario, you may spend heavily on repairs.

It’s better to find smaller leaks on time before they get large. You get to permanently seal them before they get worse. Or in some cases, till you need to completely replace your vehicle’s radiator.

Speed of performance

There are stop leaks that take just 15 minutes and there are others that take longer (30-45 minutes). Some even go as long as hours. The ones that seal up fast are the best option in case of urgency.

Does it mix well with anti-freeze?

This question should come up when shopping for the best stop leak. Radiator stop leaks that don’t mix well with antifreeze will require you to flush out the coolant before applying them. 

Stop leaks that mix perfectly with antifreeze and improve conveniences. You get to apply irrespective of what happens to the coolant.


The claim that all radiator stop leaks are the same is just not true. Radiator designs are as complex as engine designs. For instance, there are different types of radiators that could be made of: plastic, brass, copper, or aluminum. They also differ in terms of functionality. A good comparison is the cross-flow versus the downflow radiator.

With such complexity, stop leak products should be chosen carefully in accordance with the vehicle’s radiator design. If the wrong stop leak is used, clogging might occur in the radiator–causing the coolant not to flow smoothly. 


If you’re looking to save money, you can always go for the cheap ones. But you should understand that you’ll be compromising on quality. If you want to get the best, you need to spend a little extra, so that issues with your car won’t get worse. Issues like clogging in the radiator and the presence of sludge in the engine. 

Ease of use

Convenience is another factor you can consider. If you’re looking to save some space you can go for the tablet or powder radiator to stop leaks.

For a safer application of stop leak into the radiator, the tablet and fluid form is appropriate. Also, in case of a speedy effect, the powder form is the best option.

The Brand

If you just can’t seem to make a decision, you can always follow the bandwagon and choose the best radiator to stop leaks on the market by brand. 

There are various great brands in the market, some of which are great for specific designs of radiators as well as other car parts.

How Do Stop Leaks Actually Work?

In order to know how they work, you need to know what a radiator stop leak is. Radiator stop leaks are additives used to seal up minor holes in your vehicle’s radiator. It also clogs leaks in between the radiator’s components.

The common ingredients you’ll find in radiator stop leak include:

  • sodium silicate
  • ceramic fibers & particles 
  • aluminum iron & copper particles
  • ground-up almond shells

Note: You’ll definitely not find all these in a bottle of radiator stop leak.

Once poured into the radiator, the stop leak sealant circulates throughout until it’s forced into all the gaps in the radiator piping. The whole process takes place when your vehicle’s cooling system is under pressure.

The pressure will cause the particles from the sealant to bind and thereby cause them to create a temporary seal.

And that is just the basic workings of a radiator stop leak. Other sealants exist which have their own techniques in which they work. 

Types of Radiator Stop Leak?

There’re various types of radiator stop leaks. All of which work in different ways but they give similar results.

The difference is the ingredient and the form of the product. Both are going to be discussed.

In terms of ingredients we have:

  • Metallic
  • Ceramic 
  • Organic fillers

This type of radiator sealant works basically by circulating throughout the radiator system so its particles will bind and form a temporary sealant while the system is under pressure.

The con about this type of sealant is that topping off your coolant or flushing it could cause the seal to flush as well. Leaving behind pinholes.

Note: Common/Inferior radiator stop leaks have metallic, ceramic, and organic fillers as their main ingredient.nits best for a temporary sealing.

Ceramic fibers

Sealants with this ingredient succeed where the fillers fail. The difference is fiber’s special micro-sphere nano-technology which helps to create more fibrous patching on the leaks of the radiator’s piping after circulating throughout the system.

Once the system is heated, the fibers cure. Thereby creating a seal that is semi-permanent. This allows you to flush the coolant or top it off without the fear of breaking the sealed leaks.

Sodium silicate

This is a special ingredient that you’ll most likely find in popular brands of radiator stop leaks. it’s actually liquid glass that melts easily (212 to 221°F), once poured into the cooling system to fill up leaks. After sealing up, it’ll take a whole lot more heat to melt it again (At least 1490°F).

Due to its durable seal, sodium silicate radiator stop leaks are great for sealing leaks in the hot portion of a vehicle’s engine.

In terms of product type we have:

  • Tablet 
  • Fluid 
  • Powder


This is a very convenient form of radiator stop leak product. It takes up less space due to the fact it’s a small tablet that holds its shape. You can toss it into a container of water in order to dissolve and form a liquid radiator sealant. 

There are some tablet stop leaks that can mix with the coolant. So, whenever you wish to reapply a coolant you get to kill two birds with one stone.


A very common form of radiator stop leak in the market. It is usually contained in plastic bottles for easy dispensary into radiators. They come in various sizes. Large, medium, or small.


This form of stop leak contains all ingredients and particles needed to seal up leaks in your vehicle’s radiator quickly. It’s very convenient in terms of storage space. 

The same can’t be said in terms of application as you’ll need a steady hand. Or better yet a funnel to prevent a mess. A face mask is also advisable so as to prevent inhalation of the powder.

How to Use Radiator Stop Leak ?

Step 1: Check for Leaks

There are numerous ways of inspecting your radiator. It’s either by signs such as colored goop puddles, an overheating engine, or by visual inspection. On performing a visual inspection, you’ll need to open the radiator cap and visually confirm if the coolant’s level is well below what it’s supposed to be after applying it.

Note: Make sure the engine’s not running and let it cool down as well. you’ll prevent hurting yourself.

Step 2: Read the Manufacturer’s Instructions Carefully

After confirming the leak(s), it is necessary to read through your vehicle’s manufacturer’s instructions. It should contain information on the appropriate form and if necessary, the ingredients of the Radiator stop leak that’s safe for use.

This step will save your vehicle’s cooling system from clogging and your engine from sludge.

Step 3: Pour in The Stop Leak

Before taking this step you’ll need to turn off your vehicle’s engine. If it just started overheating, then let it cool down. After that, safely remove the radiator cap and then gently dispense the stop leak into the radiator.

There are various forms of radiator sealants. Each with its own method and safety precautions for dispensing. You’ll have to read your stop leak’s product instructions.

Step 4: Ignite The Engine

Once you’re done dispensing the stop leak, close the radiator’s cap and then start the engine. The engine when on will cause an increase in temperature on the radiator. This will enable the coolant to circulate the stop leak. It takes roughly 10- 30 minutes for proper circulation.

Step 5: Take The Car for Drive and Recheck for Leaks

Once you’re done with the previous step, take the car out for a drive. Or you can just start the engine and let it run for a while. Then check for leaks underneath the car and the temperature of the engine.

Step 6: Seek a Professional

If the radiator still leaks colored goop or the engine is hotter than usual, you’ll definitely need to get a professional mechanic.

Benefits of radiator stop leak

You Get to Save Money

Catching radiator leaks early is a great way to save money. If you neglect the signs of leaking, the problem may get worse and much more expensive. 

A good radiator stop leak will enable you to make the most out of your vehicle’s radiator for a lengthy period of time. Enough for you to hire a professional to perform a complete overhaul of the radiator. 

It Keeps you Safe

The best stop leak for radiator will keep your vehicle’s cooling system running. It’ll protect your car mid-drive from overheating. Especially when you’re in the middle of traffic.

It Prevents Total Breakdown

A vehicle experiencing a radiator leak will lose the coolant needed to douse the engine’s excess heat output. With the radiator in a bad condition, it’s only a matter of time for the engine to break down.


Q: Is a stop leak a permanent fix?

A: Most radiator stop leaks today are made specifically for temporary solutions. Its purpose is to buy you enough time to get a professional to work on your vehicle’s radiator. It could lead to some repair or a complete replacement.

Q: How long does stop leak last in a radiator?

A: several factors need to be considered, such as the quality and formulation of the product as well as the size of the leak. 

If the quality of the sealant is high and the leaks are small, then the sealant is bound to last longer. It’ll stay for about 10,000 miles.

The durability of the sealant shortens if its quality is low and the leaks happen to be larger. After all, radiator stop leaks aren’t permanent solutions. They can only buy time.

Q: Why isn’t stop leak working?

A: Radiator stop leaks are effective sealants. However, it’s still possible for them not to work properly and it’s not due to the sealant. There are a number of situations where the radiator stop leak ceases to plug leaks.

For instance, the sealant might not mix with the coolant, flushing them may cause the leaks to reopen.

In another situation, it could be due to leaks from other components of the radiator. Components such as the: cork gasket, water pump, coolant reservoir, main seal & front seal.

You’ll need to replace such parts if leaks are found in them. The sealants are made solely for the radiator’s piping.

Another issue with a radiator stop leak is clogging due to excess sealant. Various sealants in the market contain different strengths and filler materials. You need to read the sealant’s package to know the appropriate amount you should dispense.

Q: What are the dangers of a radiator stop leak?

A: Excessive dependency on sealants can damage your car’s engine: sealants are temporary solutions. It’ll only lead to an expensive problem if you continuously try to extend its usefulness. The end result is usually a complete breakdown.

Powdered sealants are inhalation hazards: powdered sealants are best for sealing of leaks in radiators. But its form is dangerous to your health if inhaled. Make sure to wear a face mask or try to cover your mouth or nose.

Incompatible sealant: Radiators are just as complex as engines. They require a specific type of sealant just as engines require a specific grade of antifreeze. If the wrong sealant is used, the radiator could end up clogging.

Q: Does the radiator stop leak really work?

A: yes they do. This is so because they consist mainly of formulae and ingredients that include fillers, silicate, or fibers that are great for sealing up leaks in the radiator.

If your radiator doesn’t seem to patch up, then it may be due to the large leak hole. Or some other component of the radiator happens to be leaking.


So there you have it. 10 of the best stop leak for radiators on the market. By now, you should be able to find the best sealant for your vehicle. If you haven’t made your choice yet, here are some of our recommendations:

If you’re for the best quality, we recommend the K-seal coolant Leak Repair ST5501. It may be a bit expensive, but it’s worth the price gave it’s a permanent fix and it works for most radiators.

For a smaller budget, we recommend Bar’s Leaks G12BP Powder Radiator Stop Leak. It’s great at sealing leaks quickly and it’s a permanent fix as well. 

Despite our recommendations and you still haven’t made a choice you’re welcome to make use of the guide to determine the best sealant for you.

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