PURPOSE: To improve the heat transfer and pressure resistance properties of a round type detachable oil cooler attached on the outer face of an engine block, by a method wherein each of elements which make up a core consists of a pair of disc plates and many protruding threads that intersect each other are formed on the plane faces of the disc plates.
CONSTITUTION: A core is a laminate of two or more disc elements 1 which have center holes 10 and are coordinated with each other, and accommodated in a casing 9. The casing 9 has a pair of first liquid entrance-and-exit ports that communicate with liquid entrance-and-exit ports 5 and 6 inside the elements 1 and second liquid entrance-and-exit ports 7 and 8 which communicate with the peripheries of the elements 1. Each element 1 consists of a pair of disc plates 12 which are coordinated with each other, and a group of many protruding threads 15 is formed jigzag on the plane face of the disc plate so that a band-like wave pattern is formed. The many protruding threads 15 of the pair of the disc plates 12 intersect each other and are in contact with each other at the intersections, and the disc plates 12 are jointed together by brazing.