The Garage
Car Parts
It sounds like magic, but it works.
By Andra DelMonico
Updated on May 10, 2023 11:06 AM EDT
5 minute read
Best Overall
K-Seal Coolant Leak Repair
Check Latest PriceBest Value
Bar's Leaks Radiator and Heater Core Stop Leak
Check Latest PriceHonorable Mention
Blue Magic Radiator and Block Sealer
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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
Also Consider
- Honorable Mention: Blue Magic Radiator and Block Sealer
- Honorable Mention: Bar’s Leaks Radiator Stop Leak
- Honorable Mention: Gunk Aluminum Cooling System Stop Leak
- Honorable Mention: AlumAseal Radiator Stop Leak Powder Blister Card
- Honorable Mention: Prestone Radiator Sealer Stop Leak
- Honorable Mention: JB Weld Radiator Stop Leak
- Honorable Mention: Liqui Moly Radiator Stop Leak
- Honorable Mention: 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 Coolant Leak Repair
Best Value
Bar’s Leaks Liquid Aluminum Stop Leak
Honorable Mention
Blue Magic Radiator and Block Sealer
Honorable Mention
Bar's Leaks Radiator Stop Leak Concentrate
Honorable Mention
GUNK Aluminum Cooling System Stop Leak
Honorable Mention
AlumAseal Radiator Stop Leak Powder
Our Verdict on the Best Radiator Stop Leaks
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.
Q: How long until I see results from a stop leak product?
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.
Q: Is a stop leak a permanent fix?
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.
Q: Do I need to drain the cooling system after using stop 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.
Q: What should I do if the sealant doesn’t work?
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.
