It's not so much about getting the oil out folks. Aluminum oxidizes and forms a thin layer of aluminum oxide. It melts at 2 to 3 times the temperature of aluminum.

Even if it looks shiny and brand new, it still has a layer on it. Cleaning it off is done with chemicals and the stainless wire brush. If you dont clean it off, once you have the heat high enough to melt it, the aluminum underneath will just run out like water.

Think of it like breaking the crust on a pie, once you get through the top layer everything underneath will be goo.

If you get that thin little layer off aluminum oxide off first, then you only need enough heat to form your puddle in the aluminum. And wont have the danger of melting away the good stuff.

If that makes any sense.

-Dave