Do products like Thermagasket or K W block seal work even moderately well as a temporary fix for blown head gasket and if so which brand would be preferable?

While products like Thermagasket and K-W Block Seal may temporarily seal a blown head gasket, their effectiveness is limited and cannot be considered a permanent solution. These sealants are designed to fill small gaps and leaks, but they cannot withstand the high pressure and temperature conditions within an engine. They may provide temporary relief from symptoms like coolant leaks or overheating, but it's important to understand that they are not a substitute for proper repair or replacement of the damaged head gasket.

As for which brand might be preferable, there is no clear consensus or empirical evidence to suggest a significant difference in their performance. Both Thermagasket and K-W Block Seal have their supporters and detractors, and their success depends on the specific situation and severity of the issue.

It's crucial to note that using these products should be considered only as a temporary measure to get you to a mechanic or as a way to buy some time until you can afford a proper repair. They are not a long-term solution, and continued use can potentially cause further damage to the engine.

For the most reliable and effective solution to a blown head gasket, it is recommended to consult a qualified mechanic for assessment and appropriate repair. Replacing the head gasket and any other damaged components is necessary to restore the engine's functionality and prevent more extensive damage in the future.