10 Best Radiator Leak Sealer 2025 in the United States

The ATP Automotive AT-205 Re-Seal is a versatile radiator leak sealer designed to quickly address leaks in various vehicle systems such as engines, transmissions, power steering, and differentials. One of its main strengths is its compatibility with both conventional and synthetic oils, along with a range of system fluids including ATF, gear oil, and hydraulic oil. This makes it an adaptable choice for diverse automotive needs. Additionally, it stands out by not containing petroleum distillates, which helps prevent over-swelling or damage to rubber seals and gaskets.

The product's professional strength and fast-acting formula make it effective for immediate leaks, with an emphasis on rejuvenating worn or dried seals. The 8-ounce bottle is designed to treat systems with up to a 6-quart capacity, which is suitable for most standard applications, though larger systems may require proportionate adjustments.

Its compact size and lightweight nature (50 grams) make storage and handling convenient. The ATP Automotive AT-205's ability to work across various automotive systems without risk of chemical damage to seals is notable, making it a good option for users seeking a quick and temporary fix for minor leaks across multiple vehicle components.

K-Seal ST5516 is a versatile radiator leak sealer designed for heavy-duty vehicles and industrial applications. One of its standout features is its ease of use; you simply shake the bottle, pour it into your coolant system, and let your engine run—no draining or flushing required. This convenience is a major plus for users who want a quick solution to leaks in radiators, head gaskets, and other engine components.

The product is designed to seek out and seal holes and cracks permanently, which can be a significant advantage for those dealing with ongoing coolant leaks. It’s compatible with all antifreeze types, making it suitable for a wide variety of vehicles, including commercial and agricultural machines. Its professional-grade reliability has earned it a solid reputation among mechanics.

While K-Seal ST5516 is praised for its effectiveness, it may not fix all leaks, particularly those that are very large or structural in nature. Users should have realistic expectations about its capabilities. Additionally, while its non-corrosive formula is designed to be gentle on the cooling system, some users may still worry about the long-term effects on older engines or systems with existing issues.

The Permatex 82099 Spray Sealant is designed to tackle leaks in various automotive applications, making it a solid choice for DIY enthusiasts and those looking to save on repair costs. One of its standout features is its ability to create a durable rubber barrier that stops leaks quickly, which is particularly beneficial for hard-to-reach areas where traditional sealants might not work effectively without disassembly. This product works on a range of materials including plastic, metal, and rubber, offering versatility for different needs.

While it’s effective for low-pressure leaks, it may not be suitable for high-pressure systems, which could limit its use in certain situations. Additionally, users have reported that while it can provide a quick fix, the longevity of the seal can vary, so it's not a permanent solution for all leak scenarios.

The compact 12 oz. size makes it convenient for storage and application, and its spray form simplifies the process, eliminating the mess often associated with other liquid sealers. The Permatex 82099 Spray Sealant is a helpful product for those dealing with minor leaks in automotive systems, but it’s important to recognize its limitations regarding pressure and longevity. For users who need a quick and easy solution without extensive repairs, this sealant could be a valuable addition to their toolkit.