Anyone who has done a head gasket can tell you how sparkly clean the piston is that was subjected to the (coolant) leak. Steam works. Ive taken medical capnography tubes inline with a ported vacuum source. Then the small tube into a bottle of water kept in the passenger compartment. It draws the water in via a venturi effect, so the faster the engine goes, the more water it draws. At idle it virtually draws no water. I have borescoped pistons after running a few quarts of water through and it works. Below is a picture of a capnography tube If the head is off, I would buy one of those handheld steam cleaners.