Pulled the plug today, and at first I didn't think it was all that bad. Then I started cleaning it out and realized how deep that gunk went down and how much there was. Spent two hours digging it out with a screwdriver, a large allen wrench, and anything I could use to get in there. The drain hole on the back of the block was clogged up too. I used a screwdriver and a piece of TIG welding rod to open that up again. I got a LOT out but there's still some in there. Now that I've broken it all loose I'm concerned about it getting into the radiator.
Is there anything I can pour in there that will sort of dissolve that stuff? I'm thinking maybe I can do it in a few stages. Let it sit for a few days, drain it, and do it again. Thought I saw that discussed here one time.
