10 Best Radiator Sealant of August 2025

• Permanent cooling system sealer
• Liquid glass and copper formula
• Seal withstands up to 2000 degrees Fahrenheit
• Forms permanent copper-ceramic seal
• For use in systems up to 6 gallons

Blue Magic

• RADIATORWELD: Our radiator and plastic tank repair kit has all you need for making professional quality, permanent repairs with state of the art components and easy to follow instructions.
• COUNT ON US: For more than 40 years, our products have earned a loyal following from people who take pride in their work. With each product we innovate, we continue to provide the world's strongest bond for your projects.
• SIMPLE TO USE: No removal of tank or radiator is required to stop leaks. Easily fix holes up to 3/8" diam. or cracks up to 4" long. Includes epoxy putty, fiberglass cloth, sandpaper, and applicator.
• VERSATILE & DEPENDABLE: Great for radiators, washer fluid tanks, storage tanks, water tanks, plastics, composites, PVC and more. Professionals, mechanics and avid DIYers know J-B gets the job done.
• NO PROJECT TOO BIG OR TOO SMALL: We have all the products you need to get the job done right. JB Weld always delivers the legendary performance of the World's Strongest Bond.

J-B Weld

• 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

Genuine GM

• Seals larger leaks seals
• Repairs heater core leaks
• Repairs freeze plug leaks
• Repairs blown head gaskets
• Repairs blocks

Bar's Leaks

• Small leaks blow porous joints or cracks in the cooling system are not easy to locate (that is noticed is the cool falling water levels). Radiator Leak seals such leaks immediately and completely.
• For all cooling and heating systems with water and without water filter. Also suitable for aluminum and plastic radiators. Compatible with all standard cooling stabilizers and frost protection agent. Also suitable for preventative use.

Liqui Moly

• Seals leaks
• Conditions cooling system
• Inhibits rust and corrosion
• Lubricates water pump seals
• Helps control electrolysis

Bar's Leaks

• 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

Prestone

• 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.

J-B Weld

• 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

Bar's Leaks

• REPAIRS IN MINUTES: Formulated to permanently weld radiators, including hard plastic aluminum heads and blocks in old and new cars. The only car radiator and gasket sealant university tested to meet ASTM D3147. Save time/money. US Bestseller
• SEALS CRACKS AND STOPS LEAKS: A DIY alternative to costly repairs, our coolant leak fix permanently seals cracks and holes! It quickly repairs your leaking radiator, freeze plug, heater core and water pump casing with no adverse impact on efficiency.
• POUR AND GO: Our cooling system sealer is easy to use: just shake the bottle, add to your radiator/overflow and run the engine! Unlike some traditional products, it mixes with all types of antifreeze, absolutely no draining or flushing required.
• SCIENTIFICALLY TESTED: Safe and effective, our cracked block repair can seal leaks up to 1/32 of an inch! Once cured, the repair withstands the high pressure of the combustion chamber, all without failing or clogging the cooling system.
• CUSTOMER SUPPORT: If K-Seal engine coolant leak stop doesn’t seal, the system might be over-pressurized. Check the Technical Specification section of this page for extra instructions for a successful repair. Over 8 million bottles sold worldwide!

K-Seal