LAST UPDATED: December 12, 2018

The Best Radiator Stop Leak (Review) in 2021

Best Choice Bar’s Leaks Liquid Aluminium Stop Leak Bar’s Leaks Liquid Aluminium Stop Leak
Premium Pick BlueDevil Radiator & Block Sealer BlueDevil Radiator & Block Sealer
Best Value The Best Radiator Stop Leak (Review) in 2021 Bar’s Leaks HDC Radiator Stop Leak Tablet

A pool of liquid under your parked car can be disturbing. A leak can be a very expensive problem to fix, particularly if your radiator needs replacing. Fortunately, there’s a solution: radiator stop leak sealant. This is a relatively easy fix as it can often be added straight to your cooling system. Using a clever mixture of metals, ceramic particles or fibers, the sealant can get to work in as little as a few minutes.

But what is a radiator stop leak sealant and how exactly does it work? It’s also quite controversial and a lot of people will tell you to avoid it. Are they right?

Below we’ve listed our favorite stop leak sealants. You’ll have a better idea of what stop leak sealant is best for you and also what makes them work so effectively. You’ll also understand exactly how they work miracles on leaks and can save you a few dollars.

The Best Radiator Stop Leak

Bar’s Leaks Liquid Aluminium Stop Leak is one of the most well known and loved coolant stop leaks. This radiator stop leak is able to seal radiator leaks, freeze plug leaks, and repair gasket leaks and heater core leaks. It does this by cooling the water temperature using two key ingredients: liquid aluminum and Xtreme Cool. You’re probably wondering how liquid aluminum works? Well, we can tell you that this ingredient is a top-quality feature in the new generation of stop leak products and acts by sealing leaks and also conditioning the system. The Bar’s Leaks Liquid Aluminum Stop Leak not only fixes your immediate problem but prevents further corrosion too.

A nice feature of this product is that you don’t ever have to flush the antifreeze out of your system before use as it’s been designed to be directly added to the cooling system. Liquid Aluminium works with all different types of coolant: yellow, orange, pink, red, blue and green silicate-based and non-silicate based OAT/HOAT antifreeze. It also works with water. Leaks are sealed within 20 minutes but more often than not they are said to be sealed within minutes!

Specification
  • Brand Bar's Products
  • Model 1186
  • Weight 1.2 lbs

If you’re looking for a safe and fast car radiator sealant then the ATP AT-205 Re-Seal product could be the right choice. This product is professional strength, so you know you’re getting some serious top-notch stuff when you invest in a bottle. Not only does it stop leaks fast, but it also brings all your rubber seals & gaskets in the engine, transmission, power steering and hydraulic systems back to life with its rejuvenating formula. You won’t have to worry about flushing out the system either, as this radiator sealant is compatible with conventional and synthetic oils, power steering fluids, hydraulic oil, ATF and gear oil. Although the sealant is strong enough to totally restore worn-out or dry seals it won’t harm the internal components.

This is an easy-to-use product. All you need to do is to add the liquid into your car as you would normally with oil or brake fluid. The specially-formulated liquid is designed to blend with the oil and circulate when you vehicle is being operated. The fluid is made from a plasticizer that essentially works by hardening and increasing flexibility. It gets to work in as little as five hours unless the seal or gasket is severely damaged.

Specification
  • Brand ATP Automotive
  • Model AT-205
  • Weight 2 lbs

There may be many reasons why you are searching for the best radiator sealant. Perhaps you have a head gasket leak, engine block leak, radiator leak or water pump leak…either way this product will solve your problems fast and professionally, for a fraction of the price.

It’s a simple product to use as you just need to add the K-Seal to your coolant system to create a fast and long-lasting fix. It’s also been scientifically tested and is the only coolant leak repair fluid to be carried by the AA – which is the UK’s largest roadside repair company to your coolant system, the product gets to work immediately, looking for holes and cracks to permanently fix while you’re running your engine as normal. The product has been made from a special material containing microfibres, which on contact with a gap, mesh together to form a seal. The product can repair holes of up to 0.635mm in size but won’t block any passageways or tubes within the cooling system.

The K-Seal antifreeze stop leak formula will form an extremely strong and permanent seal that is guaranteed professional results. This is why it’s such a trusted product and used by professionals in the UK.

Specification
  • Brand K-Seal
  • Model ST5501
  • Weight 9.6 oz

This product is slightly different in that it isn’t a liquid but rather a radiator leak stop in tablet form. They’re still very effective and offer really good value for the money. The Bar’s Leaks HDC Radiator Stop Leak Tablets do several things that are beneficial to your car. Not only do they seal leaks but they also help control electrolysis, lubricate the water pump seals, condition the cooling system and inhibit rust and corrosion.

They’re a good all-around product for your car and super simple to use too – just add the tablets to warm water. Bar’s Leaks coolant stop leak promises to seal external, internal and coolant oil leaks. The amazing thing is that they work from as little as 15-20 minutes and in most cases leaks will be totally sealed in this amount of time. Sometimes a second application is needed, but that is not always necessary. This product been manufactured from a well-known and trusted company. The Bar’s Leaks brand has almost 70 years’ experience when it comes to fixing automobile problems and leaks.

Specification
  • Brand Bar's Products
  • Model HDC
  • Weight 1.6 oz

This product won’t fix a radiator leak but it will almost certainly help you to discover where or indeed if you have any leaks in your system. By adding the Interdynamics Cooling System Water Leaks UV Dye it will help you to locate where the leaks are.

This is a professional grade product that contains just one application of radiator/engine cooling system UV leak detection dye. You’ll need to buy additional products to use it through such as a UV black light. It’s safe to use with all vehicle makes and models except the 1996 and newer GM models that use DEX-COOL coolant. This product is also suitable for use with all types of antifreeze except the DEX-COOL coolant.

The Interdynamics Cooling System Water Leaks UV Dye is a very reasonably priced product that has a lot of positive reviews. Just be mindful that it is a dye and it will stain your skin on contact!

Specification
  • Brand Interdynamics
  • Model 375CS
  • Weight 1.6 oz

One of the best features of the ACDelco Cooling System Seal Tabs is that they provide excellent value for money. In fact, some of the people that have used this product have even described this radiator leak repair as a low-cost miracle! This radiator stop leak might not be the best radiator sealant on the list for your particular vehicle but we believe that it’s a good all-around product.

This is an original and organic formula that has been specifically designed to be used in radiator systems. The purpose of this product is to not only seal minor leaks but it will also prevent leaks too. It has been designed from a material that seals the porosity in your vehicle’s cooling system which will, of course, prevent corrosion. Another great feature of this product is that it’s DEX-COOL compatible and totally non-toxic too.

Specification
  • Brand Genuine GM
  • Model 12378255
  • Weight 1.6 oz

This antifreeze stop leak is one of the best on the market from also one of the most tried and trusted brands in the market. The Bar’s Leaks Block Seal Liquid Copper Intake & Radiator Stop Leak will repair larger leak seals, heater core leaks. Freeze plug leaks, blocks and blown head gaskets in no time at all and for the fraction of the price, it would cost to take it to a professional.

What makes this particular radiator stop leak so special is that it’s a one-step sealer which contains an antifreeze compatible sodium silicate formula so it’s not necessary to drain your cooling system before use. With this product, you are also able to use it with water alone, however then the second bottle of Bar’s Leaks Block Seal Liquid Copper is required to add to the system once the antifreeze is installed. Not only does this product fix leaks but it also stays in your cooling system to prevent further leaks and corrosion occurring in the future.

Specification
  • Brand Bar's Products
  • Model 1109
  • Weight 1.25 lbs

This car radiator sealant offers a permanent solution for the leaks in your vehicle and has been specially designed to fix radiator and block leaks. The BlueDevil Radiator & Block Sealer is made in the USA and claims that permanent repair is guaranteed. The product works amazingly well on plastic, aluminum and metal radiators and is super safe and easy to use.

Made from a special formula with no solid or fibrous materials this product won’t harm or clog your cooling system. Instead, it bonds to plastic, cast iron, aluminum, alloy or metal and is compatible with gasoline and diesel engines. When this formula bonds to the weak points in your cooling system it then creates a permanent airtight seal that will work with the heat of your engine to expand and contract. You can add this directly to your cooling system…you just literally pour and go!

Specification
  • Brand BlueDevil
  • Model 00205

This product is a gentle non-toxic formula that is super tough when it comes to sealing leaks and preventing rust from forming. Not only this but the J-B Weld Perm-O-Seal Radiator Stop Leak solution also acts as a lubricant to the internal cooling system components. This product offers a permanent solution for your car, van, truck, bus or tractor radiator. It’s super easy to use too as you just need to pour the contents into your radiator slowly while the engine is running so the contents have space to properly circulate. This will not clog or harm your cooling system in any way – it’s a good, safe option for those looking for a cheaper option than paying for a mechanic.

With larger leaks, you can catch the fluid and keep running it through until the leak is sealed. This stuff really is the business. This is a versatile product too. The J-B Weld Perm-O-Seal Radiator Stop Leak solution can be used on a variety of different products too, not just automotive. Please check the packaging before buying to see if it is compatible with your vehicle.

Specification
  • Brand J-B Weld
  • Model DS-114
  • Weight 1.6 oz

If you want to find a product that stops leaks fast then the Preston Radiator Stop Leak won’t let you down. This radiator leak sealant has been designed with a patented formula that acts fast when it comes to stopping leaks in your radiator, water pumps, and heater cores. Another benefit that this product shares with many of the others is that it will protect your vehicle from pitting and corrosion too.

The product is said to take sealing performance to the very next level by stopping the leak as well as dealing with the corrosive condition that creates the leaks in the first place. The product has been formulated with an effective mixture of natural and synthetic fibers that can easily seal leaks up to 0.020 inches x 0.5 inches. The product actually uses the same materials found in bulletproof vests so with this product you definitely know that you’re getting some seriously tough materials! Though the product seals leaks you won’t have to worry about it clogging the radiator or heater core tubes.

Specification
  • Brand Prestone
  • Model AS145
  • Weight 12.8 oz

Best Radiator Stop Leak Buying Guide & FAQ

When it comes to taking on the task of fixing a problem with your vehicle yourself, often people are overwhelmed and daunted by the variety of products on the market. Below we have compiled a buying guide and listed your frequently asked questions to help you to make your task easier.

Things to Consider When Buying a Radiator Stop Leak

There are many components to your vehicle that need to work perfectly in order for it to run smoothly. A car radiator is one of the most important yet overlooked features as a damaged radiator will likely cause your vehicle to break down. The radiator serves an important purpose in cooling your engine down using a liquid coolant. Engines often break down when they overheat and the main reason for this is a leak in the radiator.

pouring a coolant for car overheat

One way to fix this problem is to buy a radiator stop leak that will ideally seal the leak as well as to prevent further corrosion. There are many radiator leak sealants on the market and it can be a tricky task to choose which is best for you. So here are a few things to consider first:

  • How Confident Are You With Mechanics?  It’s not a difficult task to add a radiator stop leak sealant to your vehicle but if you don’t know your gasket from your exhaust then maybe it’s best to get a professional to help you? Or at least a friend who can offer a little advice.
  • Budget  – Radiator stop leak sealants vary in price. What is your budget and if it’s on the low end of the scale then are you going to be compromising on quality?
  • Does It Require You To Flush Out Your Cooling System? – Some car radiator sealants require you to flush out your cooling system before use whereas others can be added straight to the system and mixed with the existing fluids. It’s essential you double check this before making a purchase.
  • Is It Compatible With Your Vehicle? – Again, this could be damaging to your vehicle if you buy something that isn’t compatible. Every product will say whether or not it’s suitable for your vehicle. Check first.
  • Is It A Trusted Brand? It’s really not worth buying the cheapest option at all. Take a look at the brand, read the reviews and make sure you buy something that has a totally stellar reputation.
  • Are You Sure There Is A Leak? – This might seem like a really obvious thing but have you checked to see if there’s a leak? If there is liquid on the floor underneath your vehicle then it’s likely there is a leak but it’s better to be 100% sure before you treat the issue. There are UV dyes on the market that detect leaks and are well worth buying if you want to be certain. Bear in mind that most of these dyes require a special black UV light to show up the fluid.
  • How Big Is The Leak? If the leak is fairly small then it’s likely that the radiator stop sealant will fix the problem and prevent further issues. If, however, the leak is on the large side. You’re going to either need twice the amount of liquid or seek professional help.

Leak Concerns To Keep in Mind

Radiator leak repair products need to be used at the first sign of a leak. As with anything with automobiles, the longer you leave an issue the worse it’s going to get. So if you suspect that you have a leak in your radiator, or you’ve checked and you know that you have a leak then it’s best to act fast. Leaks from your vehicle can come from a variety of different places. Not only can your engine be leaking fluid but the water pump can leak and the head gasket can also leak. Fixing a radiator leak from the inside is an almost impossible task without the use of a radiator stop leak product. This is the fastest and most economical method for fixing your car. If you suspect that the leak in your car is large, if you’ve found a lot of fluid, then you’re going to want to take your vehicle to a professional as most car radiator sealants are for relatively small leaks. If you’re unsure where the leak is located you might also want to seek the advice of a professional. Be sure to know what you’re fixing and know that although the sealants are permanent, this is, of course, dependant on the size and location of the leak.

Types of Radiator Stop Leak

Years ago radiator stop leaks would essentially stick the leak back together using gummy solutions and whilst this did temporarily fix the problem, it also caused issues in that it would also clog the cooling system passageways and heater cores  – not ideal! Vehicles have become more high-tech over the years and therefore so have radiator stop leak products. There are many different options on the market which provide different features and knowing which is the right choice for you can be difficult. Stop leak formulas are now made from a variety of different chemicals that can provide a permanent seal to your leak. Many of the products on the market have now been created with steel, aluminum, and copper which bind to make the seal. Liquid forms and tablet forms are available too – offering protection for varying levels of leakage. Check the material of your radiator and know your car and which fluids you use to maintain it before purchasing a radiator stop leak sealant.

black copper radiator of engine cooling system

Best Radiator Stop Leak FAQ:

Q:  What is a radiator stop leak?

A:  When you first discover a leak in your vehicle then there are only really two options. You can either have your radiator replaced which not only will take time but will also be very expensive. Or you can use a radiator stop leak sealant which is a product that comes in either liquid or tablet form and is used to not only form a seal on the leak but also forms a protective layer to prevent further damage. There are lots of different types of radiator stop leaks sealants on the market which vary in price and strength.

You will also notice that there are some brands that lead the way when it comes to radiator stop leak products. It’s worth buying from a trusted brand when deciding which product is best for your vehicle. Some radiator stop leak products can be poured directly into your cooling system whereas others will require you to perform a system flush beforehand.

Although radiator stop leaks are often touted as permanent, they’re not really 100% permanent. Although a high-quality radiator stop leak sealant can seal the leak, if there’s something in your system creating a leak it will no doubt return at some point down the line. Of course, this also depends on the size of the leak, but if you have a giant pool of liquid under your parked car then you’re looking at a larger problem.

You need to think of radiator stop leak sealants as a cheap yet non-permanent solution.

Q:  How does radiator leak stop work?

A:  Radiator stop leak sealants have had a bad reputation in the past as the early versions would form a gummy layer that would seal the leak but also clog up your system. Things have changed over the years and products have become better and better. If you use a stop leak sealant correctly then it can indeed seal leaks in your system, but not permanently. You’ll likely have to add the liquid again from time to time and may need to eventually replace your radiator.

Stop leak sealants are actually quite popular and used pretty often. Even car manufacturers use these products in the factory because the cooling systems in newer cars are generally smaller and even a pinhole in the system can cause a leak.

Stop leak car sealants are products which are made from a variety of materials such as ceramic particles, metallic particles and  – unbelievably – ground up almond shells! They circulate through the cooling system when your engine is running and when there is pressure in the system the particles are forced into any gaps to plug them. As we mentioned, this isn’t always a permanent solution and if you flush your coolant then the leak might return meaning that you’ll need to add more stop leak sealant.

When you buy a stop leak with fibers such as ceramic fibers or micro-sphere fibers they circulate through the system and embed in any gaps. As more fibers attach they build a strong mesh which will then harden and cure with the heat of the engine. These are more permanent types of sealer.

Q:  Do I need to drain my cooling system after using radiator stop leak?

A:  It seems there is quite a bit of confusion when it comes to draining your cooling system after using a dose of radiator stop leak. As with any other product on the market, everything is individual and there is no one answer that will work for everyone. Most radiator stop leak sealants do not require you to drain your cooling system as they have been specially designed to stay in your system and protect it from further damage. Draining your cooling system could drain away the fluid you’ve added and reveal the leak again if performed too soon. Please check the individual product for advice and if in doubt then seek professional advice.

Q:  How long does it take to see results?

A:  Again, all stop leak sealants are different and some work faster than others. Some will need at least a few hours to work with a warm engine to seal – depending on the materials used in the sealer, while others claim to form a bond within just a few minutes. Check before buying.

Q:  What are the dosage recommendations?

A:  Each product varies and will say on the packaging how much radiator stop leak sealant is required to fix the leaks. Dosage depends on your vehicle, the product used and also the size and number of leaks that you have. Some leaks will need several applications to form a strong enough bond. It’s always best to have more product in your garage than expected as you never know when you’ll need to quickly repair your car from a leak.

Our Top Pick

It’s a difficult task choosing the best radiator stop leak sealant as we understand that vehicles differ and also the size and complexity of the leaks. The product that we found was the most suitable for different vehicles and leaks were Bar’s Leaks Liquid Aluminium Stop Leak so this is what we chose for our top pick. The brand is one of the most famous on the market and Bar’s Leaks are well known to be leaders in this industry, so we feel confident about their products. These guys really know their stuff. The Bar’s Leaks Liquid Aluminium Stop Leak is able to seal radiator leaks, freeze plug leaks, gasket leaks and heater core leaks using liquid aluminum and a material called Xtreme Cool. Not only does this combination of materials in the formula treated the leaks but it’s also said to condition the system too. You won’t have to flush out the antifreeze either as it has been designed to be added to the cooling system.

This was one of the fastest products we found on the market too. Whilst other products can take up to five hours to treat leaks. This works in an impressive 20 minutes or under!

Sources:

  1. Car Repair: How to Use Radiator Sealant, Cars Direct
  2. Do stop leak products work?, Ricks Free Auto Repair Advice