Best Radiator Stop Leak – Top 10 Instant Sealants Review [Updated]


The radiator is a traditional element of an automobile cooling system as well as a home heating system, which can be applied differently depending on where it’s used. Car radiator serves for engine cooling, transmitting the motor’s heat through the water. It provokes water heating and, consequently, heats up the air, entering the cabin. Home radiators function very similarly by transmitting hot water or liquid through the pipes to heat up the air in the room.

radiator coolant leaking

As radiators contain liquids, it’s crucial to inspect your radiator regularly and cease any leaks if they start. Talking about car radiators, when you notice water under the front of your automobile when it’s parked, it means that your radiator leaks.

All metallic parts of the radiator, utilized for liquid transmitting, can be subjected to leakage, resulting in pressure decrease, corrosion of the zone close to the leak plus reduced overall performance of the cooling system. Actually, vacuum-based systems may lose much heating because of leakage troubles.

In case if valves leak, it’s required to exchange the details as the problem can’t be fixed by simple repairing. If the piping system leaks, it’s easier to get rid of this defect. Usually, patches are fixed mechanically. Or, if you need immediate fixing, you are free to purchase a stop leak radiator liquid or powder, which will seal the hole for some time until you will have time for major repairs.

And now, we are eager to introduce ten outstanding radiator stop leak items. This list was formed according to various reviews along with real tests, held to discover what items are really efficient and what is just a waste of money.


K-Seal ST5501 Permanent Radiator Stop Leak

K-Seal ST5501 Multi Purpose One Step Permanent Coolant Leak Repair , BLUE
8,710 Reviews
K-Seal ST5501 Multi Purpose One Step Permanent Coolant Leak Repair , BLUE
  • Permanent Coolant Leak Repair - Just Shake, Pour And Go.Fit Type: Universal
  • Mixes With All Antifreeze
  • No Draining Or Flushing
  • Fixes Cracks And Leaks In Radiator, Head Gasket, Freeze Plugs, Cylinder Heads, Heater Core, Water Pump Casing And Engine Blocks

K-Seal is one of the most experienced manufacturers of stop leaks and knows how to create top-quality sealants. Dealing with liquid sealants, the brand offers products safe for all types of radiators. And tests proved that this stop leak doesn’t harm any radiator.

Being trusted by many car owners and professionals, this item is believed to have a good impact on the entire cooling system. During the tests, the radiators were in great condition after damages had been repaired. Though, it’s not clear if the further action was favorable.

Be ready that this sealant may be rather costly and, actually, it’s one of the most expensive solutions for leakage problems. Thus, you’d better use it only for small leaks and if you know what exact kind of radiator you own.

Additionally, this item has a long-lasting effect though there is no assurance that it can serve as a permanent solution of the problem. So, it’s still recommended to acquire a fresh radiator, especially if you plan a long journey.

Apparently, K-Seal is the most efficient tool for dealing with radiator leaks. It’s apt to fix serious problems as well as give a long-lasting effect. Nevertheless, it’s still a temporary solution to the radiator damage.


Bar’s Leaks 1186 Liquid Aluminum Stop Leak

Bar's Leaks 1186 Liquid Aluminum Stop Leak - 16.9 oz , Gray
2,693 Reviews
Bar's Leaks 1186 Liquid Aluminum Stop Leak - 16.9 oz , Gray
  • Bar's Leaks Liquid Aluminum Stop Leak seals radiator leaks. Seals freeze plug leaks. Repairs gasket leaks and heater core leaks. Lowers water temperature.
  • Seals radiator leaks
  • Seals freeze plug leaks
  • Repairs gasket leaks
  • Special Shipping Information: This item cannot be returned and has additional shipping restrictions

Having been in business for a while, Bar’s Leak brand has already created many formulas for various kinds of radiators.

Specifically, this product is applicable for aluminum radiators and it’s not recommended for others. The sealant may also seal outside leaks in hoses or other elements of the cooling system and is known for its efficient work.

This item copes great with slow leaks while its efficiency with heavy leakage may be reduced. It’s apt to seal hairline cracks pretty fast along with dealing with some more serious problems. However, during tests, it didn’t master to seal the majority of radiators, K-Seal coped with.

If to apply this item correctly, you can prolong the lifespan of your radiator for a week or two. Though, you will still need to acquire a fresh radiator.

This sealant is a good choice for aluminum radiators and slow leak troubles. It’s possible to seal the leak easily and for a while if to follow all the instructions.


ATP AT-205 8-Oz Re-Seal Bottle

ATP AT-205 Re-Seal Stops Leaks, 8 Ounce Bottle
16,282 Reviews
ATP AT-205 Re-Seal Stops Leaks, 8 Ounce Bottle
  • Professional strength fast acting resealer, stops leaks fast
  • Rejuivinates all rubber seals & gaskets in engines, transmissions, power steering, differentials and hydraulic systems
  • Compatible with conventional and synthetic oils, ATF, gear oil, power steering fluids and hydraulic oil
  • Does not contain petroleum distillates, will not over-swell or breakdown seals
  • 8oz bottle will treat a 6 quart capacity, adjust accordingly

It’s the proper choice if you need non-toxic plus quick sealant. Basically, this item is a high-quality professional liquid apt to provide you with efficient assistance. Besides sealing leaks, it also renovates rubber seals and gaskets, gearbox, power steering plus hydraulic systems. This item is able to regenerate outworn or dry seals without harming any internal elements. Additionally, it functions decently with conventional and synthetic oils, hydraulic oil, gear oil, ATF, and power steering fluids.

As the liquid is absolutely non-difficult to use, you simply need to add the sealant to the radiator as you usually do with oil or brake fluid. It functions by mixing up with the oil and circulating when the motor is run. Being made of plasticizer, this product hardens and raises flexibility. If the seal and gasket are in order, this liquid starts its effect in 5 hours after you add it.


Bar’s Leaks 1109 Block Seal Liquid Copper Intake and Radiator Stop Leak

Bar's Leaks 1109 Block Seal Liquid Copper Intake and Radiator Stop Leak - 18 oz.
798 Reviews
Bar's Leaks 1109 Block Seal Liquid Copper Intake and Radiator Stop Leak - 18 oz.
  • Seals larger leaks seals
  • Repairs heater core leaks
  • Repairs freeze plug leaks
  • Repairs blown head gaskets
  • Repairs blocks

Old versions of automobiles frequently keep copper radiators. If your radiator is made of copper, you must be very careful with the choice of the proper products as this material may cause problems for some sealants.

This Bar’s block seal liquid is good for temporary repairs of copper radiators, having no bad impact on the cooling system.

Bear in mind that the item may face difficulties in dealing with big leaks or coolant leaking on the driveway as it was initially created for pinholes and hairline cracks.  Though, it’s very efficient for minor leaks.

Though this sealant is marketed to cope with block fixing, no mechanics advise applying any chemical fixes for a block until you are forced to do that in the worst extremity and have no opportunity for a real fix.

Still, if it’s just used as a radiator stop leak, it’s rather reliable and can serve as a temporary resolution of the problem for a week or two until you are prepared to acquire a new radiator.

Thus, this item is suitable if you have a copper radiator featuring minor leaks. It will avert the expansion of damage until a fresh radiator is installed.


Dike Temporary Radiator Stop Leak

This Dike item is the appropriate product for immediate and fast repairs in emergency cases. Besides, it may serve to prevent damages to any system, functioning under difficult conditions.

It goes well with every kind of radiator coolant, including green and orange ones. Additionally, it can be utilized for radiators of any vehicle, from a mini car to a van or tractor.

The manufacturer advises adding 1 pint for every 4 gallons of radiator’s capacity or 4 ounces per gallon. Just add the necessary amount of sealant to the radiator, change the radiator cap and run the motor for about 15 minutes.

The item functions efficiently thanks to its innovative formula, which seals any leak it finds, protecting the automobile and maintaining necessary temperatures.


J-B Weld DS-114 Perm-O-Seal Radiator Stop Leak

J-B Weld DS-114 PERM-O-Seal Radiator Stop Leak - 0.7 oz.
220 Reviews
J-B Weld DS-114 PERM-O-Seal Radiator Stop Leak - 0.7 oz.
  • JB WELD PERM O SEAL : Is a specially formulated non-toxic compound ground to a very fine particle size to quickly mix and flow into all areas of the cooling system to find and seal leaks.
  • WHAT THE PROS USE: Mechanics, repair pros, and any avid DIYer knows our products bond strong to a variety of surfaces in even the toughest environments; and they have always been made in the USA.
  • MONEY SAVING REPAIR SOLUTION: The powered concentrate allows for an economical repair as compared to liquid based alternatives that use similar technology.
  • DURABLE FAST FIX: The special compound will quickly seal leaks and will also act as a rust inhibitor and lubricant to internal cooling system parts. It will not clog or harm your cooling system.
  • DO IT YOURSELF: Big or small, you can DIY it with J-B. Our heavy duty adhesives repair & restore it right the first time. JB Weld delivers the legendary performance of the World's Strongest Bond.

By acquiring this item, you can be sure in its excellent quality. Being absolutely non-difficult in the application, this harmless sealant will efficiently cope with any leaks. Moreover, it is apt to perform the functions of a rust inhibitor along with lubricating the internal cooling system.

Its main advantage is that it’s able to ensure a permanent solution to the leakage issues no matter if you have a car, truck, van, bus, or anything else.

Being regarded as one of the greatest sealants in comparison with liquid substances, this J-B Weld product will provide you with good quality repairs at reasonable money. What makes it even more astonishing is that it causes no block or harm to the cooling system.


Genuine GM Fluid 3634621 Cooling System Seal

Genuine GM (12378255) Fluid 3634621 Cooling System Seal Tablet - 4 Grams, (Pack of 5)
922 Reviews
Genuine GM (12378255) Fluid 3634621 Cooling System Seal Tablet - 4 Grams, (Pack of 5)
  • Non-toxic
  • DEX-COOL compatible
  • Engine application is based on liters of volume in cooling system
  • Formulated for automotive use
  • For use with all vehicles

This item is available in the form of pellets and serves as a non-expensive and efficient remedy.

Furthermore, this sealant is commonly added to the GM vehicles during the manufacturing process to avert any hairline fractures, which may appear in the radiator.

Principally, this cooling system seal is employed for aluminum radiators, but it goes well with other materials, including copper. During the tests, these tablets didn’t cause any harm to test automobiles.

Bear in mind that you need to discover the amount of coolant in the system and add a determined amount of sealant, which may be bulkier in comparison with liquid substances and cause some inconveniences while being added. Thus, you’d better find out the amount of sealant you need prior to starting adding it to the radiator.

This item is an outstanding remedy for hairline fractures, but it’s not created for the serious leak. It serves as a temporary resolution of the trouble and even after applying it, turn to a professional at the first opportunity.

Besides, it’s not clear how long such a seal will perform its functions. It can cover pretty large holes and provide immediate assistance in case of emergency but don’t count on its durability. If to talk about small leaks, these pellets can serve longer, but still not permanently.


BlueDevil Radiator & Block Sealer

BlueDevil 00205 Radiator & Block Sealer - 16 Ounce
116 Reviews
BlueDevil 00205 Radiator & Block Sealer - 16 Ounce
  • Permanent repair for radiator and block leaks.
  • Works effectively on plastic, aluminum and/or metal radiators
  • Contains no solids or fibrous materials.
  • Safe and Easy to use.
  • Guaranteed

Being created in the United States as a continuing resolution for radiator and block leaks, this radiator and block sealer is apt to save you from any leakage. Creators of this product assure that it performs permanent repairs and is applicable for plastic, aluminum plus metal radiators along with being absolutely safe plus non-difficult in use.

Thanks to its special composition featuring no tough and filamentary materials, the sealant makes no damage or block to the cooling system. It attaches to plastic, aluminum, metal, and cast iron along with being appropriate for gasoline and diesel motors. Once, it finds the weak spots of the cooling system, it attaches to them, creating a permanent seal, functioning in connection with the motor heat, expanding and contracting. The item can be poured straight into the cooling system and no additional steps are required.


AlumAseal ASBPI12 Radiator Stop Leak Powder Blister Card

AlumAseal ASBPI12 Radiator Stop Leak Powder Blister Card - 20 g
287 Reviews

Alumaseal Radiator Stop Leak Powder Blister Card is pretty affordable but is often sold as an additional item to other orders. Besides, you are free to purchase the brand’s clip strip of 12 blister cards.

This item can be utilized for every material and is compatible with every coolant type and anti-freeze additions in the cooling system. Be sure that it won’t block the vehicle’s cooling system.

Besides, it’s easy to use. After pouring the powder into the radiator, make certain that it’s not warm before you take away the cap. After closing the cap, make the motor run for several minutes. This item will be efficient for radiator coolants up to 22 quarts.


Prestone AS145 Radiator Stop Leak

Prestone AS145 Stop Leak Repair for Radiators, Heater Cores, and Hoses, 11 oz, 1 Pack
201 Reviews
Prestone AS145 Stop Leak Repair for Radiators, Heater Cores, and Hoses, 11 oz, 1 Pack
  • Patented formula quickly stops leaks in radiators, water pumps, and heater cores
  • Boosts corrosion inhibitors to protect against pitting and corrosion, which cause radiator leaks
  • Combination of natural and synthetic components provides the ability to seal leaks up to 0.020" x 0.5"
  • Seals even large leaks without interfering with the flow through the radiator or heater core
  • Stops the leak as well as the corrosive condition that causes it

That’s definitely a great solution to leakage problems. Being patented by a prominent brand, this formula reaches the desired result every time it’s applied. It provides immediate assistance and stops any leaks quickly and efficiently, allowing you to drive a car having no worries about the radiator.

Besides, Prestone AS145 is able to avert corrosion in the cooling system. As corrosion may lead to leakage, by preventing corrosion you will decrease the chances to face any serious leak. Consequently, your automobile will function steadily and effectively.

In case of bad seals, this item may increase their functionality by renovating them. So, this product is very useful and is easy to use. It will help to get rid of leaks up to 0.020×0.5 inches.


What’s Important to Know While Opting for a Radiator Stop Leak?

Having read the reviews above, you may come to the idea that K-Seal ST5501 is the most proper option. It copes with leaks of any size and is applicable for almost every model of a radiator as a temporary resolution until you are able to substitute the radiator.

Many people consider stop leak to be car snake oil, but, actually, the main function of many products is to prevent the expansion of a gap and give you some additional time for buying a new radiator. No more.

Having read our reviews, you already know what sealants work the best for various types of radiators, what exact functions they perform, what troubles they may solve, and how long their effect lasts. The most important for you is to make certain that the item you choose is suitable for your radiator.

We can’t tell for sure, but the stop leaks, which were created for a certain type of radiator, may be more efficient. Yet, their limited functions are a sign of a more accurate chemical reaction.

Meanwhile, sealants in the form of powder or pellets are usually more affordable. Giving the identical effect as their liquid rivals, these sealants are more lightweight after being dissolved. Moreover, they don’t occupy much place in a car if you plan to store them there for extreme cases.

Nevertheless, liquids are easier to use as they are usually created to suit a specific size of the cooling system while some pellets may be rather bulky.

Anyway, no matter what exact product you choose, any of them will provide you with immediate assistance in the worst extremity and will seal the leak efficiently, prolonging the durability of a radiator and allowing you to drive for some time before its replacement.


Tips on Radiator Stop Leak Use

Aspiring to cope with the problem fast and efficiently, make certain that you act according to the instructions on the sealant package as well as some general outlines. Proportions of stop leak may be different for various radiators and there can be some additional guidelines like shaking the bottle or something else. Besides, powders and tablets may have some specific directions in comparison with liquids. Always stick to the amount of sealant, advised by the manufacturer. Don’t use too little or too much as you may fail to reach the desirable effect, breaking the application rules.

  1. To start, allow the automobile to cool down and take off the radiator cap. Never do that immediately after making a stop as steam may be directed just into your face. Crack the pressure deliberately. Never hurry up while doing that.
  2. Add the stop leak to the radiator and warm up the motor to its normal temperature. By watching the ground under your car, you will notice when the leakage stops. After that, run the motor for several minutes more before turning off the ignition.

Not all manufacturers write that on packages, but it’s advisable to flush the system until it gets cool as no one needs the presence of some extra fibers or low melting point metals in the radiator. Some sealants may block the radiator or have some other negative impacts on it. So, never consider sealants as the permanent resolution of the trouble and always read reviews before buying them.

To be on the safe side, you are free to flush the entire system one more time, and only after that, add antifreeze to the cooling system. Clearly, it’s better to use the liquids, recommended by the auto manufacturer.

It’s crucial to examine the temperature and fluid level regularly until you acquire a fresh radiator. The sooner you substitute a radiator the better. Clearly, sealants may make your radiator function properly for a great number of miles, but no guarantees are provided and sooner or later the problem will emerge again.

Bear in mind that all tests were made, strictly following the guidelines and proportions, recommended by stop leak producers. The effect can differ if you apply the sealants in other proportions and fail to follow other directions. Moreover, there can be no effect at all if guidelines aren’t followed.


To Sum It Up

In a nutshell, K-Seal products remain the most reliable ones and provide the most long-lasting effect. That’s why we recommend using ST5501 to stop the leak. Of course, this sealant is rather pricey, but it can be employed one more time. You are free to store it in your garage or automobile for immediate assistance in extremity cases. Moreover, don’t forget to take it with you if you plan a long journey as it can be a real wonder stick if you are far away from the city and any automotive shop.

All the other sealants can be used as well. But bear in mind that no stop leak will be able to restore the radiator entirely and be a permanent solution to the leakage problem. All of them are just temporary fixes and no one knows how much a car can run after such a repair. So, start to seek a new radiator in any case no matter what sealant you use to cover the gap in the radiator.

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