This isn't quite a straight forward answer, as a lot may depend on exactly what type of leak it is?
Holts Radweld Plus is the result of a project to improve the standard Holts Radweld product. By improving the formulation, it is now able to seal a wider variety of leaks within the coolant system, including those in the engine block and cylinder head areas which the standard Holts Radweld is not designed/recommended for. This is due to the super concentrated nature of the new formulation for Holts Radweld Plus. The improvements also mean it is able to seal larger holes in larger systems more effectively than other products.
Holts Radweld Plus is designed to seal coolant to air leaks in the engine block and cylinder areas. The way the product works is that it stays in a very diluted form (effectively in a liquid form so it will not block water passageways) while in the coolant system, it is circulated around until it finds the hole, then it is forced through the hole by the pressure of the system. When it is exposed to air/atmosphere on the other side and has the heat of the engine behind it, it is able to form a seal in the hole/crack. The rest of the Radweld not involved with this seal will still stay effectively in a liquid form inside the system until the system is flushed/drained. So, Radweld has the ability to stay in the system and help seal holes as and when they occur, while also helping to stop corrosion within the system.
If the head gasket leak is internal, meaning a leak from the coolant passages into the combustion chamber, or a leak between the oil and coolant systems (oil into water or water into oil), it is unlikely that Holts Radweld Plus will seal these leaks due to the vast pressure differences between the combustion chamber/cylinder heads and the coolant system.
In these internal leak cases, Holts Wondarweld would be the product recommended for use by an experienced DIY mechanic. The repair process is much more complicated: the fault would have to be diagnosed correctly in order to follow the specific instructions for each type of leak, and spark plugs would have to be removed to decompress damaged cylinders while the engine running to reduce the pressure differences between the two systems, allowing Holts Wondarweld into the leak site in order to seal it.
answered 4 years, 10 months ago