overheating on 1999 Cadillac Catera

99 cadillac catera overheated and water that come out of resevoir left an oily residue. Blown head gasket?

2 answers 1 comment
very likely. get it leak down test to confirm.

Is this something I can do or do I have to take it to a mechanic to get it tested.
Bad coolant/oil heat exchanger. Common problem.