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The Best Radiator Stop Leak 2021

Radiator Stop Leak

When the radiator in your car begins to malfunction, you may find yourself having issues with your car overheating. If engine coolant is pouring out from the radiator, you can temporarily stop the leak by using a radiator stop leak solution.

The best radiator stop leak is the K-Seal ST5501, which mixes with all antifreeze and is a permanent coolant leak repair that requires no draining or flushing.

Temporarily preventing  antifreeze leaving your radiator is highly recommended in order to avoid further issues. Radiator stop leak solutions come in the form of a liquid formula and solid tablets where both effectively work to stop leaks.

Table of Contents

Best Radiator Stop Leak

Radiator Stop LeakTypeQuantity
K-Seal ST5501Liquid8.0 oz
Bar's Leaks 1186Liquid16.9 oz
Dike TemporaryLiquid16.9 oz
J-B Weld DS-114 PERM-O-SEALTablet6 Tablets
Bar's Leaks HDCTablet10 Tablets

Fixing a leak in your radiator can be easily fixed with one of these radiator stop leak solutions. They work with fibers that chemically bond together to form a barrier against the leak. This can be achieved via liquid or solid tablet form and is a temporary fix to keep your car running smoothly until you are able to properly fix it.

Many of the solutions within this article even have the added benefit of acting as a head gasket sealer but be sure to read the exact features on the bottle.

Using one of these temporary repair solutions is a cheap and effective method of getting your car back on the road. Below is a list of the best radiator stop leak solutions that are easy to use and allow you to drive your car until its fixed properly.

K Seal Permanent Coolant Leak Stop

The K Seal Coolant Leak Repair is a reliable radiator leak stop that can be used for a variety of different purposes. From head gasket, freeze pumps, heater core, cylinder heads, water pump casing and engine blocks, the K Seal is suitable.

It uses microfibers that mesh together and is specifically designed to work within your car’s system, so it doesn’t stop the cooling system from working efficiently. This repair formula is easy to use and you can quickly apply it anytime you notice a leak.

Here are some of the notable features of the K Seal ST5501:

  • Shake and pour application
  • Doesn’t require draining or flushing
  • Works with any type of antifreeze
  • Fixes cracks and leaks in your radiator
  • Comes with helpful instructions
  • Made in the USA

K Seal ST5501 is easy to use and works permanently, so you don’t have to worry about a leak coming back after you have repaired it. Overall, it is the best radiator stop leak that does the job in hand with ease and offers great value for money.

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Bar’s Leaks Liquid Aluminum Radiator Stop Leak

Bar’s Leaks is a popular brand for radiator stop leak solutions and this one in particular is made using liquid aluminum. It is reliable stop leak and you will not need to worry about the leak making a reappearance after you have applied this formula.

In addition to just fixing the leak, this solution also contains a component called Xtreme Cool. This lowers the water temperature in your system and prevents it from overheating. Here are some of the features of the Bar’s Leaks Liquid Stop Leak.

  • Works for radiator and gasket leaks
  • Made in the United States
  • Seals instantly
  • Works with existing antifreeze
  • Can be used with water alone to lower temperature
  • Works within 10-20 minutes

This solution is convenient and works very quickly to solve leaks in your system. However, it’s not suitable if you have a very large leak – it’s much more effective on pesky smaller leaks. Bar’s Leaks has become a very respected brand of radiator stop leak, and it’s one that works on many different cars and engine leaks.

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Dike Temporary Radiator Stop Leak

If you are planning on getting your radiator replaced, but need a temporary solution to repair your engine, the Dike Radiator Stop Leak is a reliable option for you. It works quickly and will protect your engine from damage after a leak.

It will also not interfere with your antifreeze or block any passages in your engine. Here are some of the notable features of the Dike Temporary Radiator Stop Leak.

  • Results in less than 15 minutes
  • Works with any type of antifreeze
  • Seals internal leaks and gasket leaks

This affordable solution is a great temporary fix for a leak in your radiator. If you are planning on getting your radiator fixed, this solution will extend the life of your car’s engine until you are able to make that change.

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J-B Weld Radiator Stop Leak

The J-B Weld Radiator Stop Leak is a non-toxic compound designed to permanently repair your radiator and protect your engine. This stop leak is particularly unique because it supports the internal functioning of your engine by lubricating the inner channels and preventing rust from forming.

This stop leak compound is unique because it isn’t a liquid, which most other radiator leak stoppers are. Instead, it is a solid compound that is grounded down into extremely fine particles. When the particles are poured into the radiator, they mix into the system and then naturally move towards the leaks and seal them.

Here are some of the notable features of the J-B Weld Radiator Stop Leak.

  • Seals leaks and acts as a rust inhibitor
  • Permanent repair
  • Will not clog the cooling system
  • Made in the US
  • Contains water lubricants

Overall, the J-B Weld Radiator Stop Leak is one of the best tablet options and you have peace of mind that its developed by a reputable brand.

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Bar’s Leaks HDC Radiator Stop Leak Tablet

This is another reliable product by the Bar’s Leaks brand, but instead of a liquid, this is a solid tablet that you can use to repair leaks in your radiator. To use, all you need to do is pre-dissolve the tablets in water and then put them into your radiator.

They will not only close up leaks, but they will also prevent rust from forming and keep your system lubricated. These particles are very versatile and will stop many different types of leaks, whether they are internal or external.

Here are some of the notable features of the Bar’s Leaks Radiator Stop Leak Tablet.

  • Seals internal, external and coolant to oil leaks
  • Prevents rust and corrosion
  • Conditions and lubricates internal system
  • Controls electrolysis
  • Made in the United States

These versatile tablets work well to both repair leaks in your radiator and keep your entire engine running smoothly. They are permanent leak stoppers that you can rely on to prevent further damage to your system. Bar’s Leaks is one of the most reliable brands of stop leak products, and this tablet is one of their many products.

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Radiator Stop Leak Buying Guide

If you notice your radiator has a leak, it’s important to get it taken care of right away. If it continues, the leak could cause serious damage to your car and even put you in harm’s way while you are driving.

Although you may want to consider further repair or replacement of your radiator, a stop leak product is a good way to close up the leak right away so you can drive safely.

There are many different radiator sealant products on the market, and if you aren’t a car expert, it can be difficult to determine which one is going to be most effective for your needs. Here are some of the factors you should consider when purchasing a radiator stop leak solution for your car.

Liquid vs. Tablet

There are two main types of radiator stop leaks – liquid products and tablet products. Generally, they both work well to patch up any leaks you may have found in your radiator, but they are different, and it’s important to know the differences between the two before buying.

Liquid formulas are very easy to use – all you have to do is pour the liquid into the radiator and then let your car idle for them to work. With tablets, you may need to predissolve them in water before you put them in the radiator.

However, tablets are more likely to provide rust protection and lubrication to keep your engine running well.

Radiator Leak Stop

Compatibility With All Types of Antifreeze

Since the stop leak solution will be going directly into your car’s radiator, it’s important that it doesn’t negatively interact with the antifreeze in the car. To ensure this doesn’t happen, look for a stop leak product that works with all different types of antifreeze. This will give you total peace of mind when putting the stop leak into your radiator.

Different Types of Leaks

Another thing that’s helpful to look for is a stop leak for radiator that can work on different types of leaks. There are both internal and external radiator leaks, and they need to be repaired slightly differently.

However, most serious products can repair both types of leaks. It’s also helpful to look for a product that can repair gasket leaks as well. The more versatile your radiator stop leak is, the more use you will get out of it.

Repair Time

When searching for a radiator stop leak, you should also look at how long it takes the product to work. Typically, you will need to put the product into the radiator and then let your car idle for a certain amount of time so the solution can completely seal up the radiator. Some products work faster than others, and while this isn’t a deal breaker, it’s always helpful to have a product that works quickly.

Coolant Stop Leak

Temporary vs Permanent

Some radiator sealants are designed to be permanent, while others will only last for a designated period of time. When purchasing a stop leak product, you will need to consider what your needs are. If you are planning on taking your car in fairly soon, then a temporary solution may be all you need.

However, if you want to go a little longer before getting your car serviced, then a ‘permanent’ solution will likely be better. Regardless of which one you opt for, you should take your car in for service at some point after you notice a radiator leak, just to make sure everything is safe and to get any necessary replacements.

Other Benefits

Some radiator stop leaks do more than just close up the leak – they actually keep your car in good condition as well. Many radiator solutions will lubricate the interior of the car’s cooling system to keep it running smoothly, and they can prevent rust and corrosion from happening as well. Not all radiator stop leaks are designed to do this, so if you want this feature, be sure to check the product description before making a purchase.

Clogged Cooling System

Another helpful thing to look at is the consistency of the solution. If it is too thick, it could clog your car’s cooling system, causing more trouble than it is worth. If you are concerned about this problem, look for a solution that uses fine particles to repair the leak. Although a solution with very fine particles may not work as well on larger leaks, it will prevent your system from becoming too full and clogging.

Radiator stop leaks feel like a miracle product when you are dealing with car engine troubles. It’s helpful to always have a radiator stop leak solution on hand in case of an emergency so you can get back out on the road again quickly.

Since your safety depends on the effectiveness of this product, it’s important that you find one that works efficiently to plug up radiator leaks quickly. Use the factors discussed in this guide to ensure that you are purchasing a high-quality radiator stop leak solution.


Using your car without the correct amount of coolant can cause a serious amount of damage to your car with overheating issues. Replacing the radiator itself would be the best repair for your car but that can be expensive and time consuming.

However, the purpose of a radiator stop leak solution is to allow you to temporarily stop coolant leaking and allow you to get on the road. All of our recommendations are fairly cheap but do the job in hand.

procarreviews author

Written By Dan

About the Author

Dan is an automotive journalist and owner of over 10 cars ranging from supercars, tuned cars, classics and your good old beater cars. He always likes to get his hands dirty with nut and bolt restorations or detailing sessions using the best products on the market.

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