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Seeing a puddle of coolant under your car is never a good thing. Whether it’s coming from your radiator, water pump, heater core, freeze plugs, or other portion of your cooling system, it can mean big trouble for your vehicle if you don’t attend to it quickly. Luckily, there is a way to stop the flow of leaks without a costly, immediate repair. Radiator stop leak is designed to stem the flow of liquid out of your cooling system without blocking those narrow passages so vital to the proper circulation of coolant.
Available in a variety of liquid, pellet, and powder forms, stop-leak products are designed to be poured into your radiator where they circulate with your coolant to seal leaks. Additionally, most offer lubrication protection for your water pump and seals. Stop leak can be a very easy and inexpensive way to avoid a big headache; here are some of our favorites.
Summary List
- Best Overall: K-Seal Multi-Purpose One Step Permanent Coolant Leak Repair
- Best Value: Bar’s Leaks Liquid Aluminum Stop Leak
- Honorable Mention: Blue Magic Radiator and Block Sealer
- Best Value Runner-Up: Bar’s Leaks Radiator Stop Leak
- Best Premium: Blue Devil Radiator & Block Sealer
Our Methodology
I’m a car enthusiast, and I understand the desire to keep a vehicle on the road is intense and necessary. I took several factors into consideration when compiling this list of the best stop leaks. I focused heavily on the brands we all trust already with other service items.
But I also recognize that price matters, so I included other brands that also provide good results but with lower price tags. Just make sure to do your research to ensure that the stop leak you chose will be good for your application. For more information on our methodology, go here.
Best Radiator Stop Leaks Reviews & Recommendations
Best Overall: K-Seal Multi-Purpose One Step Permanent Coolant Leak Repair
This K-Seal leak repair provides a tight seal to your cooling system quickly and efficiently. One of the best features is that it is simple to use and can be applied instantly to your coolant system. It’s capable of being added to either a hot or cold engine, saving your time. However, use extreme caution when mixing the solution with a hot engine to avoid hurting yourself. Another benefit of K-Seal’s leak repair is it mixes with all types of antifreeze, so you need not worry about buying a specific brand for your car. It also can be left in the cooling system or flushed out if needed. K-Seal’s formula is designed to target holes and cracks then permanently seal them without damaging your engine.
While this may be an excellent radiator fluid stop leak, there are a few drawbacks you should be aware of. K-Seal does guarantee a permanent seal, but many consumers report they experienced some leaking again a few weeks or months after application. This could be due to the size of the crack, but it should still block small holes without issue. Another problem is it tends to clog easily and is a bit on the pricier side.
Best Value: Bar’s Leaks Liquid Aluminum Stop Leak
Bar’s Leak is well-known for its stop leak products, and among the best is its Liquid Aluminum Stop Leak. The compound making up the fluid works great at sealing leaks, and it also conditions the engine with the use of what Bar’s Leaks call Liquid Aluminum. That’s just stepping one. Step two is known as the Xtreme Cool formula. This solution stops overheating and reduces the temperature of the water in the radiator. Another great feature is how durable and effective this stop leak is. It easily seals leaks in plastic, aluminum, and metal radiators, heater cores, gaskets, and freeze plugs. One other benefit is this stop leak can be added to the cooling system without having to flush out the antifreeze. It can also be used with all types of coolant, including yellow, orange, pink, red, blue, and green silicate-based and non-silicate-based antifreeze.
Even if the price is a bonus, you may have to buy in bulk to get more efficient results. Another downside is you will have to wait up to 20 minutes with the engine idling to ensure all the cracks are properly sealed. However, as with all of the products mentioned here, it is not a permanent solution and your vehicle will need to be treated again or taken to a mechanic.
Honorable Mention: Blue Magic Radiator and Block Sealer
Permanently repair and seal your radiator and block with CarGo’s liquid glass and copper-colored radiator stop leak. It’s a liquid formula that’s designed to repair and bond with your radiator materials. It works in heavy-duty applications, industrial, farm, marine, and automotive equipment. To use, pour it directly into your radiator, and it’ll start to work within five minutes. It’s durable enough to withstand up to 2,000 degrees Fahrenheit, making it durable and long-lasting. It doesn’t contain any fibrous or solid material, so it won’t necessarily clog your radiator or cooling system.
The downside of this stop leak product is that it’s best suited for large-capacity engines. This could make it more than necessary for the repair of a small car radiator. It also doesn’t dry clear, which can be unattractive.
Best Value Runner-Up: Bar’s Leaks Radiator Stop Leak
Seal the leaks in your radiator with this concentrated formula from Bar’s Leaks. It works to seal small leaks in your radiator or heater core. Bar’s Leaks manufactures this product in the United States. One bottle can treat up to 4 gallons. This formula will address drips and leaks that occur from regular wear and tear or aging of your system. This concentrate works with all types and colors of antifreeze coolant and/or water. This makes it versatile and easier to use. The concentrated formula means you only need one bottle for a regular-sized cooling system. It will work with most 6-, 8-, and 10-cylinder engines. For 4-cylinder engines, you only need half a bottle.
Unfortunately, this concentrate isn’t effective at sealing larger leaks or leaks that are located in the seams, bolts, or other areas of the system. It also won’t protect against overheating.
Best Premium: Blue Devil Radiator & Block Sealer
Whenever leaks pop up, Blue Devil’s products are sure to be recommended. Radiator leaks are no exception. This stop leak is a viable solution for all radiator types, whether they’re made of aluminum, plastic, and so on. It features no solid or fibrous materials and is completely safe for your engine. Still, it remains incredibly effective and can provide a permanent seal for leaking coolant systems.
The only downside to Blu Devil’s radiator sealer is that it’s pretty expensive. It’s more than triple the cost of other options. Even if the expense is worth it, that will drive many to skip right past it.
Our Verdict
If you want a reliable and efficient radiator sealant, consider the K-Seal Multi Purpose One Step Permanent Coolant Leak Repair. You can save a bit of money and still get a great stop leak fluid with Bar’s Leaks Liquid Aluminum Stop Leak.
Types of Radiator Stop Leaks
Powder
You will see powder stop leaks that come in different formulations and amounts. However, they all generally function the same. Pour the powder into your radiator and let it get to work. This option is simple and easy to use. However, it tends to be less effective than other solutions because you need enough powder to mix in without being so much that it clogs your radiator.
Tablets
This type of stop leak isn’t a popular one, but you will still be able to find a few options in this form. There are two methods for application. The first is to drop the tablets into your radiator and let them get to work. The other option is to dissolve them in some water and then pour that mixture into your radiator. Once in your radiator, the dissolved particles will heat up and seal the cracks.
Liquid
Liquid forms of stop sealant are much more common and have a lower viscosity. This makes them move more smoothly through the radiator fluid while also reducing friction. These tend to be made up of additives that help corrode rust and are thicker to fill leaks and reduce dirt and grime.
Key Features
Ease of Application
Look for a stop leak that matches your knowledge and skill level. Some require you to flush the entire system before adding the sealant. This may be beyond your skill level or be inconvenient due to the location of the car. If you’re stuck on the side of the road or have little experience with working on your car, then look for one that doesn’t require flushing.
Additives
Additives in radiator stop leak fluids work to remove debris, neutralize acidity, and fill leaks. Some stop leak formulas will include additives that protect your system from corrosion and rust. These are a good option if your car is older as they will help preserve your car and run smoother. Other additives help to make the stop leak more durable so that it expands and contracts with the changing temperature of the engine.
Compatibility
Before choosing the best radiator stop leak, you need to read the label carefully. Not all anti-leak fluids will work for every car. Many are specifically designed for certain models like Honda or Ford or engine types such as diesel or gasoline. You should also confirm that the stop leak formula bonds with the material you’re trying to repair. Some bond with several materials, while others are aluminum, steel, or plastic specific.
Pricing
At most, you’ll spend about $30 on radiator stop leak products. These aren’t expensive items.
FAQs
You’ve got questions. The Drive has answers.
This can be a difficult question to answer, and it all depends on the type and manufacturer of the stop leak. Many need at least 10 to 20 minutes to fully take effect, while others need a few hours. The size of the crack or hole also matters; the larger the crack, the more time it will take to fill it properly.
While stop leaks may seem like a permanent solution to your problem, they only last a short amount of time. To truly fix a leak for good, you will need to take your car to a mechanic to get a better understanding of the leak.
Generally, most radiator stop leak fluids do not require you to drain the system after applying the solution. However, read the labeling to see what the manufacturer recommends.
Remember, not all radiator stop leaks are permanent. If you don’t see an improvement after applying the fluid, you may need to take it to a mechanic for a more in-depth diagnosis.
