The following materials are usually used for the water pipe of the auxiliary kettle of the automobile:

1. Rubber: Rubber is one of the common water pipe materials, which has good flexibility and sealing property and can withstand certain pressure and temperature. Rubber water pipes are usually used to connect the auxiliary kettle and the main water tank, as well as other cooling system components.

2. Polyvinyl chloride (PVC): PVC water pipes have the characteristics of corrosion resistance, high temperature resistance and wear resistance, and are suitable for parts that need to withstand high temperature and pressure in automobile cooling systems.

3. Polypropylene (PP): Polypropylene water pipes have good heat resistance and corrosion resistance, and are suitable for connecting auxiliary kettles and other cooling system components.

4. Nylon: Nylon water pipes have high wear resistance and high temperature resistance, and are suitable for environments that need to withstand high temperature and high pressure in automobile cooling systems.

5. Stainless steel: Stainless steel water pipes have good corrosion resistance and high temperature resistance, and are suitable for connecting water pipes of auxiliary kettles and other parts, which can provide higher durability and stability.

When selecting the material of the water pipe of the automobile auxiliary kettle, it is necessary to consider its high temperature resistance, pressure resistance, corrosion resistance and other properties to ensure that the water pipe can work normally in the cooling system and has a long service life. According to the specific vehicle model, cooling system design and working environment, selecting the appropriate water pipe material can improve the reliability and stability of the cooling system. If you have any questions or need more professional advice, it is recommended to consult an automobile maintenance expert or manufacturer.