Hmmm, I really don't want to explode myself. I might look into the steaming clean at a radiator shop. That's not a bad idea.

I see guys using acetone to clean metal before welding all the time. Why is that not an issue? Is it because it is open air and not closed up in a drum? Would leaving the cap and petcock off help?

If I can avoid cutting and rewelding I'll do that. Thanks for the input.