Re: Brass radiator what sort solder and flux? With the appearance of aluminum and plastic radiators I fear this is another dying art/skill. Aluminum flux: normally dependant on temperature array and The bottom steel that you are working with. Aluminum fluxes are also hard to find in community merchants and https://angeloihcsk.blogsidea.com/33428479/everything-about-types-of-solder-to-use-on-aluminum-radiator