Fixing cracked cylinder heads with liquid glass products containing sodium silicate involves draining the coolant from the engine and then introducing the sealant mixture into the cooling system. After the sealant is in the cooling system, the next step in sealing the cracks is to run the engine at idle for a few minutes several times to heat the sealant and force it into the cracks. Afterwards, the coolant system must be flushed and coolant replaced to complete the repair.
Sodium silicate is commonly known as liquid glass because it forms a gel when heated that has the appearance of glass. This gel is an excellent sealant for small cracks in the gasket or walls of an engine cylinder, and many anti-freezes already contain sodium silicate to help seal these cracks as they occur. More severe cracks may require the specific application of a liquid glass sealant as described here, but some cracks may be too severe for a liquid glass sealant to help. Sealants are also not necessarily permanent fixes and sometimes require re-application after a year or less of driving.
It is necessary to both drain the cooling system and remove the spark plugs from leaking cylinders before introducing a mixture of liquid glass sealant and water into the cooling system. After introducing the sealant, the engine is run for intervals of 5, 15 and 20 minutes with breaks in between to allow the engine to cool and the liquid glass sealant to set. It is also good practice to add additional water to the cooling system during these breaks to replace any water lost during the idling period.