I have used Cast Blast with great success. It is cast iron grey color. I use for a lot of things now. The local machine shop sprays a light coat on all there machined surfaces once they are done if they do not plan to assemble the parts soon to prevent rust. I did the same on my iron heads for my 351-W after I bead blasted them inside and out. Two years and 10,000 miles later I pulled the valve covers to check my rocker arms and the paint was still there,did the same with the inside of my
oil pan with same results. All that hot
oil did not wash it away. The only thing this stuff does not like is gasoline. It will just about wash off the paint on first contact. It seems pretty resistent to heat though. I have also used it on front suspension parts such as lower control arms and tie rods and drag links to keep them from rusting and keep them looking good for the show car croud.
David