A method for manufacturing a plastic fuel tank including: a) inserting a plastic parison including two distinct parts into an open two-cavity mold; b) inserting a core, bearing at least part of a reinforcing element configured to create a link between the two parison parts, inside the parison; c) pressing the parison firmly against the mold cavities, for example by blowing through the core and/or creating suction behind the cavities; d) fixing the part of the reinforcing element to at least one of the parison parts using the core; e) withdrawing the core; f) closing the mold, bringing its two cavities together to grip the two parison parts around their periphery to weld them together; g) injecting a pressurized fluid into the mold and/or creating a vacuum behind the mold cavities to press the parison firmly against the mold cavities; and h) opening the mold and extracting the tank.

A temperature adjustment mold capable of performing local temperature adjustment in an axial direction from the inside of a preform while restricting shrinkage and deformation of the preform, for adjusting a temperature of an injection-molded bottomed resin-made preform includes a rod portion inserted into the preform and extending in the axial direction of the preform. The rod portion includes an annular projection portion that protrudes in a radial direction of the rod portion and contacts an inner peripheral surface of the preform. The rod portion contacts a bottom portion of the preform to restrict shrinkage in the axial direction of the preform. The projection portion restricts shrinkage in a radial direction of the preform, conducts heat between the rod portion and the preform, and adjusts a temperature at a predetermined part in an axial direction of the preform.