Yes, we know that radiator stop leak formulations have somewhat of a bad reputation among car enthusiasts, and there’s a good reason for that fact. Between inferior early formulations of this product and car owners who tried to push these products beyond acceptable use, it’s easy to see why there have been plenty of failures with some of these products.

However, that doesn’t mean that there aren’t great stop-leak products available that solve the problem of leaking radiators. Sure, these products aren’t miracle workers and won’t replace the need of having to buy a new radiator eventually, but they can be a great stop-gap that can help the car owner get just a little more life out of their radiator before having to purchase a new one. Having said that, below are our favorite radiator stop leak products currently available.

Best Radiator Stop Leaks – Reviews & Buying Guide

10Johnsen’s 4918 12-Oz.

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When used as directed by the label, this radiator stop leak is designed to stop small and very slow leaks. It’s also designed to be easy to use and all the car owner has to do is add it directly to the vehicle’s coolant, no other preparations are needed. As this product works its way through the radiator system, it will stop the small annoying leaks many vehicle owners are plagued with having. And it’s also safe to use and won’t clog up the radiator system. Although it doesn’t work as well with larger or faster leaks, it is an inexpensive temporary solution for some people.

Pros:

  • Works well on slow, small leaks
  • It’s reasonably priced
  • Easy to use
  • Won’t clog radiator systems

Cons:

  • Doesn’t handle larger leaks well
  • Doesn’t last very long

9Bar’s Leaks J-100 DiFM Treatment

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Bar’s Leaks is a company that’s well known for treating a number of vehicle leaks including power steering leaks, head gasket leaks, and even main seal motor oil leaks. Therefore, it really shouldn’t be surprising that they also make several products that deal with radiator leaks and the J-1000 DiFM is one of these products. Although this product is designed to be used before radiator leaks start, it does do a decent job at stopping smaller, slow leaks when used appropriately. This product also inhibits the formation of scale and rust in the radiator and helps to lubricate the water pump seal.

Pros:

  • Designed as a preventive radiator measure
  • Lubricates the vehicle’s water pump seal
  • It inhibits the formation of scale and rust

Cons:

  • Can only stop small leaks

8Bar’s Leak 1150-4PK 16.9-Oz.

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When properly used according to the manufacturer’s directions, this product is capable of plugging a variety of small leaks that may pop up in radiators. It’s a two-part formula that’s easy to use, but requires that the user idle or drive their car for anywhere from 15 to 20-minutes before it sets. This product is compatible with a number of different coolants include green, blue, yellow, orange and red coolants. And since it has a carbon-fiber formulation, it’s also capable of preventing future leaks from occurring and to help prevent boil overs.

Pros:

  • Stops a variety of leaks
  • Provides protection against future leaks

Cons:

  • Doesn’t stop leaks long enough

7Bar’s Leaks 1109-6PK 18-Oz.

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This product is designed to address a variety of different coolant system leaks. It’s designed to stop leaks in not only the radiator but also in the heater core, in the intake manifold and the gaskets. It also stops leaks in blocks, heads, and freeze-plugs, and the coolant system doesn’t have to be drained in order to use it. This liquid copper formula uses a special antifreeze-compatible ingredient known as sodium silicate that allows it to perform without the user having to follow a bunch of unnecessary steps. It’s a low-cost coolant leak stop.

Pros:

  • Stops radiator, block, head and gasket leaks
  • No draining required

Cons:

  • It’s only a temporary fix

6K-Seal ST5501 Leak Repair

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This stop leak product is designed to be extremely easy to use and all that needs to be done to get it to work is to give it a little shake, pour it into the radiator and allow it to work its magic. This product easily mixes into any and all types of antifreeze, and there’s never any need to drain or flush the radiator before using it. Once applied, this product will not only seal cracks and leaks in the radiator but will seal a variety of leaks include ones in the freeze-plugs, the head gasket, the cylinder heads, the heater core, and the engine block.

Pros:

  • Stops a variety of leaks
  • Seals radiator cracks

Cons:

  • May not stop larger leaks

5Irontite All-Weather Seal 16-Oz.

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All that has to be done to get the most out of this radiator stop leak product is to pour it right into your radiator. Once inside the radiator, its formulation dissolves and remains suspended in the antifreeze so it can get its job done. This product will then begin to stop leaks that not only exist within the radiator but will also handle leaks in the cylinder heads, the head gaskets and in the engine block. Formulated for use in either gasoline or diesel engines, and for use in either aluminum or cast iron blocks, this product is a solution that almost everyone can rely on to get the job done.

Pros:

  • Seals most small leaks quickly
  • Product is easy to use

Cons:

  • Doesn’t seal all leaks

4AlumaSeal ASBPI12-12PK

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Not every radiator stop-leak solution comes in oil or liquid metal form, as proven by this product. This stop-leak product is in powder form so that it’s not only easy to use but doesn’t make the same mess that liquid sealing products produce. It’s also a product that can be used with all different types of antifreeze and will not only stop leaks but will inhibit rust and lubricate the water pump. Although it won’t stop all leaks permanently, it does do a good job with smaller leaks and is a great solution for anyone with an older vehicle that is looking for a temporary radiator leak fix.

Pros:

  • Easy to use
  • Not messy at all
  • Works well on most small leaks

Cons:

  • Only stops small leaks temporarily

3Bar’s Leaks 1186 Liquid Aluminum 16.9-Oz.

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Radiator and heater core leaks are a real pain, so it’s important to get a solution that will tackle these problems if they arise. And that’s exactly what Bar’s Leaks 1186 Liquid Aluminum is designed to do. Each 16.9-ounce bottle can easily be added to a radiator, without having to drain it first, and it will immediately begin working to seal leaks. Although the vehicle owner does have to drive the vehicle for 20-minutes after it’s been applied for best results, once that’s done it does a great job of sealing all kinds of leaks. This product will repair gasket leak, radiator leaks, and even freeze-plug leaks easily and effectively.

Pros:

  • Stops leaks well
  • The product is easy to use
  • Provides better than temporary results

Cons:

  • Vehicle must be driven for 20-minutes afterward for best results

2Bar’s Leaks HDC Radiator Tablets

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To some people, it may seem odd to buy a stop leak product that’s in a tablet form, but the concept actually works pretty well. After all, they’re easy-to-use and don’t make the mess that is often associated with oils and/or liquid metals. And they can be kept in a vehicle until it’s time to use them without worrying about them spilling all over the place. But the real effectiveness of this product is that it seals leaks and conditions the cooling system while it does it. Once used, this product will also inhibit rust and corrosion and go a long way towards lubricating water pump seals. And it does it while sealing leaks.

Pros:

  • Easy to use
  • Seals leaks
  • Conditions cooling system
  • Inhibits rust

Cons:

  • Doesn’t handle larger leaks

1Dike Temporary Stop Leak

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Designed to handle small leaks immediately, this temporary radiator stop leak is suitable for just about anyone who’s developed a radiator leak and need a little time to get it fixed. Once applied to a radiator, this product will begin to work in seconds and doesn’t need all of the setup time that other stop leaks products tend to need. This product will not only seal radiator leaks, though. It will also help gaskets seal better and will help seal any internal leaks that may exist, thereby helping prevent antifreeze from seeping into the engine. All things considered, it’s a good product that works with all types of antifreeze and gets the job done well.

Pros:

  • This product works quickly
  • Handles all types of small leaks
  • This product is easy to use
  • This product helps seal gaskets

Cons:

  • Fixes only small leaks

More products also worth checking out:

Radiator Stop Leak Guide

Although radiator stop leaks have been around for decades now, they have only really come into their own in the past few years. That’s because the first ones which were formulated either didn’t work well or if they did work well, they ended up gumming up the entire cooling system. Fortunately, things have changed for the better, but that doesn’t mean that the user should just relax their guard, and buy any product available. There are still a few things to consider before you buy one of these products and pour them into your radiator.

Stop Leak Products History

One of the things that most people would be amused about finding out is that most of the early stop leak products were derived from botanical origins. Yes, these early formulations were made from plants and nuts which naturally collected where the leaks in the radiator were located. As can be imagined, this resulted in some mixed results, with some products being capable of clogging up the radiator just as well as fixing the leaks.

Things are a lot better nowadays, however. Manufacturers of these products have extensively designed and tested their products to work exceptionally well. After all, a company isn’t going to sell too many radiator stop leak products if their products tend to clog up the radiator it’s used in. As a result, consumers can depend on these products a lot more than they could in the past.

How to Use Radiator Stop Leak

Once you’ve come to the conclusion that you need a radiator stop leak product for your leaking radiator or gasket, then you are going to want to keep a few things in mind from buying the product all the way to using the product. Below are some of the steps required to use these products well and use them in a way that’s beneficial to your vehicle and actually stops the leaks in question.

Purchase the Appropriate Sealant: The first thing that you are going to want to do is find the best radiator sealant possible. This means one that not only meets quality standards but is designed for the vehicle you’re using it on. Although there are sealing products designed to be used with all vehicles, there are also ones that are only meant to be used with certain vehicles and/or coolant types, so it’s important to buy one that’s compatible with your car and your coolant. Many of the brands in our above top ten list can be used with a variety of different vehicle and coolant types.

Read Product’s Directions: It’s extremely important to read ALL of the directions included with your sealant. And you should not only read them but follow them exclusively. If the directions happen to disagree with any of our suggestions, then disregard what we have written here and follow the package’s directions. That’s the only way to ensure your product works the way it’s designed to work.

Pour It Into The Radiator: Make sure that your product doesn’t require the radiator to be drained or flushed before it’s used. If it does, then that will need to be done before continuing. Once that’s done, open the radiator, and pour the recommended amount of product into the radiator. If the instructions direct you to top off the radiator with coolant, then do that next. Once done, apply the radiator cap.

Start the Car: Most of the sealant products on the market require the car to be idled or driven for 15 to 20-minutes before the product is able to work. So, start the car and allow the engine to warm up. Once warm, allow it to run approximately 15 to 20-minutes. Allow the car to cool adequately and then fill the radiator with a 50/50 mixture of coolant and water.

Allow The Car To Sit Overnight: One of the reasons many radiator stop leak repair jobs fail is that some people fail to let their car sit for the appropriate time. After the above procedure, most products require the car to sit for at least 12-hours before it can be driven any distance. This allows the product to set up. If this process is skipped, then it can result in an inferior seal being formed and thereby a leaking radiator.