Thats what i did and it worked, but i mixed it with coolant before pouring it into the tank as i heard it is less likely to clog something that way.

This sounds as if it is too much for Radweld.
Wondarweld may be worth a try, especially if you plug the crack with steel wool (if possible) but it sound like a pretty serious leak so it may need new radiator. The best advice would be to contact your local mechanic for specialist advice.

This depends on the nature of the crack. Minor cracks in the cooling system should be fine but it would not be able to fix major cracks affecting the fuel system.

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.

No, due to the high pressures involved in the cylinders Holts Radweld Plus 250ml would be unlikely to solve your problem.

Its worth trying to use this product to stop the leak. However I would always recommend seaking proffessional advice to prevent long term damage to the engine.

Radweld Plus is designed to solve cooling system leaks in the engine
block and cylinder areas, coolant-to-air only, so if you are not sure where
the leak is and it's "coolant to air" leak then Radweld Plus should be
able to repair it.
If you are not sure if it's internal or external leak, or where the leak
is, then Holts would recommend you should try Wondarweld, since it was
designed to permanently seal cracked cylinder blocks, internal and
external leaks in the water jacket. If you have doubts consult with a qualified specialist.

The 250ml bottle treats up to 21L systems. If the coolant capacity is 7L or less, use only half bottle.
Add either into the radiator or overflow reservoir (expansion tank), top up with recommended coolant if needed.
Radweld Plus is compatible with all forms of Anti-Freeze so there should be no problem with introducing it to a coolant system containing Anti-Freeze.

Its worth trying to use this product to stop the leak. The way that Holts Radweld Plus works is it stays in solution (basically in a liquid form) while in the coolant system, the system circulates it around and when it finds the hole it uses the pressure of the system to leak through this hole. Now when it is exposed to air/the atmosphere on the other side and it has the heat of the engine behind it, it is able to form a seal over the hole. The rest of the Radweld not involved with this seal will still stay in solution inside the system until the system is flushed/drained.

Yes Holts Radweld Plus can be used for sealing a leak within the heater matrix, provided the leak is not too severe. The way the product works is it stays in solution (basically in a liquid form) while in the coolant system, the system circulates it around and when it finds the hole it uses the pressure of the system to leak through this hole. Now when it is exposed to air/the atmosphere on the other side and it has the heat of the engine behind it, it is able to form a seal over the hole. The rest of the Radweld not involved with this seal will still stay in solution inside the system until the system is flushed/drained.
As the leak is in the heater matrix section, it is likely that you will need something like a 20-30 min drive with the cars interior cabin heaters turned on in order to open up the heater matrix side of the system and allow the Radweld solution in to find and seal the leak. If the leak is not sealed during this period, the engine may need to be run for longer as the temperature around the leak site or lack of flow of Radweld to the leak site are the causes of it not being able to seal the leak.

Of course during the drive we would recommend keeping an eye on the temperature of the system as well as the level of coolant in the system, especially if it is a severe leak which could lead to the system emptying and then overheating before Radweld is able to fix the problem.