The present invention relates to a temporary protecting device (10) for use in a motor vehicle comprising: a closing part (12) configured to obstruct an opening of a filler head for a tank during assembling of the tank on the motor vehicle; and an elongated part (14) extending from the closing part (12), the elongated part comprising a first end fixed to the closing part and a second free end; wherein the elongated part is configured to allow to manipulate the temporary protecting device so that an assembly of the temporary protecting device and the filler head is movable between a temporary position and a final position, and wherein the closing part (12) is made of elastomer. The present invention further relates to a filler head (30) of a SCR tank comprising such a device and to a method for assembling such a filler head on a motor vehicle, as well as a method for assembling a car body on a car frame.