Abstract: An oil tank cap adapted to be removably engaged with an oil tank having an oil storing space. The oil tank cap includes a cap body, an air seal, and an air valve. The cap body includes an outer casing, and a cap base being plastic and one-piece, and defining an accommodation space with the outer casing. The cap base has an annular seat portion that has at least one exhaust hole, a tube portion, a separation portion having at least one ventilation hole. The air seal has a protrusion portion, and an annular body that encircles the ventilation holes. The air valve is inserted into the tube portion, is connected airtightly to the air seal, and is operable to open or close for balancing pressure of the oil storing space and pressure of an external environment.

Abstract: An oil tank cap is adapted to be removably engaged with an oil inlet of an oil tank. The oil tank cap includes a cap body that is one-piece, that is plastic, and that includes a cap portion adapted to be disposed outside the oil inlet, and a plug portion extending from the cap portion along a central axis of the cap body and adapted to extend into the oil inlet. The plug portion has a surrounding surface that surrounds the central axis of the cap body, a base surface, an accommodating slot extending through the surrounding surface, and at least one recess formed in the base surface, extending towards the cap portion, and being isolated from the accommodating slot. The oil tank cap further includes a spring strip that has a positioning portion disposed in the accommodating slot, and two abutting portions extending outwardly of the accommodating slot.