[hatzie]

I didn't know the whole situation. Just trying to be thorough and not leave anything out.

You may end up replacing several freeze plugs since it sat with coolant in it. I would not assume there's not a bunch of rust inside the block behind the freeze plugs at this point. Voice of experience.

Heat adds energy to the chemical reaction that accelerates the action of the caustic cleaning chemicals on rust and calcium/silica scale deposits. You can do the radiator cold but it will likely not work as well as circulating it through the cooling system for 15 or 20 minutes at 195°F. It also won't clear out the heater core and other hoses.

A brandy new radiator is right around $100. Aluminum will pit pretty badly under calcium scale. If it's too nasty inside it'll probably leak as soon as you remove the scale. It may be just as well to use it as a sacrificial part when you do the caustic flush and replace it with the new radiator when the rest of your cooling system is fresh and clean.