How Radiator and Coolant 'Stop Leak' Products Work

How Radiator and Coolant 'Stop Leak' Products Work

24th Apr 2019

woman behind the wheel

Fix a Coolant Leak

If your vehicle is losing coolant, you might be wondering whether a "stop leak" product will solve your problem. With the exception of a small number of air-cooled engines, most automotive combustion engines are cooled with a solution of antifreeze and distilled water. Known as coolant, it's one of the most important fluids in your vehicle, carrying heat away from the engine and to the radiator where it's released through the front of your vehicle.

Radiators or other components of your vehicle's cooling system, however, can leak. When a leak occurs, coolant may escape, resulting in lower cooling efficiency and, potentially, engine overheating. The good news is that there are dozens of products designed to seal radiator and cooling system leaks. Known as stop leak products, they are often used on older vehicles when the cost of a full repair isn't financially feasible.

How Stop Leak Products Work

Stop leak products are designed to seal leaks in radiators, coolant hoses and gaskets by plugging them with some type of material. They usually come in bottles that you pour directly into the radiator (wait until your engine is cool to open the radiator, of course). As the stop leak product flows through the radiator and cooling system, it will collect and harden at small leaks, essentially stopping the leak.

Different types of stop leak products use different ingredients to seal leaks. One of the most common ingredients found in stop leak products, however, is sodium silicate. It works particularly well when coolant and exhaust gases are leaking together. Also known as liquid glass, it hardens when exposed to heat, such as hot combustion gases, to form a seal.

Should I Use a Stop Leak Product on My Vehicle?

There's no guarantee that a stop leak product will fix a leaking radiator or cooling system. With that said, many drivers have successfully used stop leak products to temporarily or even permanently stop a coolant leak. 

The ideal solution is to repair the leak -- or replace the leaking component, depending on what's causing the leak -- but this isn't always an option. If you have a blown gasket that's leaking coolant into one or more cylinders, you may have to spend up to $1,000 to replace the head gasket. Assuming your vehicle is old, it might not be worth paying $1,000 to replace the head gasket, in which case a stop leak product may work.

Keep in mind that some stop leak products carry the risk of clogging your radiator and heating core. If you're going to use a stop leak product, choose a high-quality product offered by a reputable company.

stop leak graphic