Top 10 Radiator Sealants (April 2024)

Bar's Leaks 1186 Liquid Aluminum Stop Leak – ⭐ Best Overall Radiator Sealant

1186 by Bar's Leaks

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

ST5501 by K-Seal

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!

ST5516 by K-Seal

REPAIRS IN MINUTES: Create a permanent weld within the entire coolant system, including on hard plastic radiators and aluminum heads and blocks in larger capacity engines, AG, RV etc. The only industrial coolant sealant university tested to meet ASTM D3147.
SEALS CRACKS AND STOPS LEAKS: Avoid expensive downtime, our coolant stop leak will permanently seal cracks and holes! Quickly repair your head gasket, block, leaking radiator, freeze plug, heater core & 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 competitive products, it mixes with all types of antifreeze, no draining, flushing or pulling the thermostat required.
SCIENTIFICALLY TESTED: Safe and effective, our Heavy Duty Coolant stop leak repair seals leaks up to 1/32 of an inch! Once cured, it withstands the high pressure of the combustion chamber, without failing or clogging the cooling system. US Bestseller
CUSTOMER SUPPORT: If our engine coolant leak doesn’t seal your head gasket, 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. Save time/money

N62020 by Super Glue

401224-6 by K&W

Easy Pour and Go Formula!
Permanently fixes head gaskets, engine blocks, cooling systems, and cylinder heads.
"Contains 3 unique technologies. Military-Strength Fibers create multi-layer repair over cracks with a web-like weave. Nanotechnology permanently fixes the smallest cracks and crevices. Cool-X Conditioner – lowers operating temperature as it circulates through cooling system."
Seals larger holes with less fluid loss than competitive products as proven by lab test (ASTM D6107)
Works with all antifreeze or plain water.

1196 by Bar's Leaks

PLT11 by Bar's Leaks

AS145 by Prestone

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

DS-114 by J-B Weld

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.