how do you tell them apart? easy just look at them the blocks are a completely different shape. first link is alum 2nd link is iron Dead giveaway is the fact that you can see the indentations around the cylinders on the aluminum block. I would higly recommend that you use a good quality name brand pre-mix antifreeze with the aluminum block. At the very least if you mix your own coolant with water use only distilled water. Electrolytic corrosion eats those block pretty badly.