Abstract: A method for the application of a thermal spray coating to the cylinder wall portions of an aluminum engine block casting is disclosed in which the casting is inverted and water is caused to flow through the cooling passages of the engine block in a series flow from one end of a bank of cylinders to the other while the block is supported on a fixture that seals the cooling passage outlets in the head of the block. The fixture further permits the spray of a metallized coating onto the cylinder walls without adherence of the spray to the fixture or to other portions of the block.