What Rock said pull the side freeze plugs and tow it to a car wash & blast the innards with the wand. Before that yes I would use a caustic cleaner & not sure which type would be the best & if it is possible to use one that is too corrosive tho when you make an informed choice I'd wanna leave it in there for longer than what you mentioned tho that would depend on what type/strength of cleaner you end up going with. I've heard something about the ionized water also. With it cleaned then k.i.s.s. good green Prestone/ionized (or distilled) water whichever your choice ends up being/sacrificial anode. reportedly a few drops of dish soap is good for a water wetter for heat transfer and a bit of baking soda for acid neutralization. I wouldn't go crazy with any non standard ideas. Sounds like you have a bit of OCD, I can relate