A DIESEL FUEL PRE-FILTERING SYSTEM, equipped with: a. a structure for housing at least two filtering areas; a fuel inlet area; and a fuel outlet area; and b. an inspection window equipped with a drain for water; wherein: i. the system comprises a first filtering area with a first filtering component structured so as to define a restriction connection between the fuel inlet area and the subsequent filtering area; ii. the system comprises a second filtering area with a second filtering component structured so as to define a restriction connection between a preceding filtering area and the fuel outlet area; and iii. the structure and the inspection window are composed of thermoplastic materials distinct from each other and connected to each other by a permanent bond, wherein the structure and the inspection window are bonded by means of welding; and wherein the system further comprises: a. an upper structure for positioning the filtering components which comprises: i.a support base for the filtering component of the first filtering area; ii.an empty axial extension (9.1) for housing the filtering component of the second filtering area, wherein the empty axial extension (9.1) comprises openings along its length, such as to guarantee that the filtering component is rigid, and also to permit passage of the fluid from the first filtering area to the second filtering area; b. a base disc to support the filtering component of the first filtering area, with the base disc comprising a distal peripheral area welded to the internal wall of the structure; c. an empty structure positioned between the filtering components (6,7) of the first and second filtering areas, equipped with radial projections (10.1, 10.2) at the ends, with a first radial projection (10.1) mounted between the outer wall of the empty axial extension (9.1) and the internal surface of the filtering component of the first filtering area. a. a structure for housing at least two filtering areas; a fuel inlet area; and a fuel outlet area; and b. an inspection window equipped with a drain for water; wherein: i. the system comprises a first filtering area with a first filtering component structured so as to define a restriction connection between the fuel inlet area and the subsequent filtering area; ii. the system comprises a second filtering area with a second filtering component structured so as to define a restriction connection between a preceding filtering area and the fuel outlet area; and iii. the structure and the inspection window are composed of thermoplastic materials distinct from each other and connected to each other by a permanent bond, wherein the structure and the inspection window are bonded by means of welding; and i. the system comprises a first filtering area with a first filtering component structured so as to define a restriction connection between the fuel inlet area and the subsequent filtering area; ii. the system comprises a second filtering area with a second filtering component structured so as to define a restriction connection between a preceding filtering area and the fuel outlet area; and iii. the structure and the inspection window are composed of thermoplastic materials distinct from each other and connected to each other by a permanent bond, a. an upper structure for positioning the filtering components which comprises: i.a support base for the filtering component of the first filtering area; ii.an empty axial extension (9.1) for housing the filtering component of the second filtering area, wherein the empty axial extension (9.1) comprises openings along its length, such as to guarantee that the filtering component is rigid, and also to permit passage of the fluid from the first filtering area to the second filtering area; i.a support base for the filtering component of the first filtering area; ii.an empty axial extension (9.1) for housing the filtering component of the second filtering area, wherein the empty axial extension (9.1) comprises openings along its length, such as to guarantee that the filtering component is rigid, and also to permit passage of the fluid from the first filtering area to the second filtering area; b. a base disc to support the filtering component of the first filtering area, with the base disc comprising a distal peripheral area welded to the internal wall of the structure; c. an empty structure positioned between the filtering components (6,7) of the first and second filtering areas, equipped with radial projections (10.1, 10.2) at the ends, with a first radial projection (10.1) mounted between the outer wall of the empty axial extension (9.1) and the internal surface of the filtering component of the first filtering area.