Someone on here gave me the excellent tip of using Cascade dishwasher soap in the cooling system before draining, too. I had flushed my trucks system a few times with clear water coming out, then I tried the Cascade. I couldn't believe how much crud and brown stuff came out when I flushed it after running that through it. As a matter of fact, I did it two more times after it was rinsing clear the first time, and I got a repeat show of brown, rusty crud the 2nd and 3rd time, too. There are quite a few posts on this, and the whole affair of crudded up rear lower blocks. Next winter, when it's time to dismantle/repair tin/paint my truck, I'm going to open up the freeze plugs and replace the old rear drain (I hear it will be a bear to get it off), and clean that baby out! Oh, yeah, I also used CLR for one flush too. It also brought out more gunk.
