The blue Holts Radweld temporarily blocked my radiator (I did not open it incorrectly when I poured it) and after a year I saw that it had also stuck to the thermostat at the contact point! Perhaps the instructions should have mentioned replacing the coolant and flushing the cooling system. When I poured the black Holts Wondarweld, I isolated the radiator by connecting the pipes together and changed the thermostat after application. I did not see it sticking, though.

The Holts Wondarweld has instructions to flush the engine before and after use!! It is also poured directly into the thermostat position for direct contact with the cylinder head gasket. The exhaust gas test kit showed that the gasket was repaired. It is better to isolate the radiator, replace the thermostat, and replace the coolant! Easy solutions do not work properly!