Which statement about hydraulic systems is true regarding fluid types?

The statement that fluids must be specified in the manufacturer’s manual is accurate because hydraulic systems are designed to operate with specific types of fluids, which have unique properties such as viscosity, lubricating ability, and chemical compatibility. Manufacturers provide these specifications to ensure the system functions correctly and efficiently, as the wrong fluid can lead to performance issues, potential damage, and safety hazards.

For instance, hydraulic fluids may contain additives that enhance their properties, such as anti-corrosion agents or flame resistance. Using an incorrect fluid can compromise these properties, which affects the overall performance of the hydraulic system. Additionally, different systems may have materials that are sensitive to particular fluids; hence adhering to the manufacturer's manual is crucial.

The other options do not hold true in the context of hydraulic systems. Not all fluids can be interchanged due to these specific requirements. Furthermore, fluids in hydraulic systems can vary in color and odor depending on the additives and base oils used. Lastly, replacing hydraulic fluid with any convenient liquid is dangerous and impractical, as it can lead to system failure and safety risks.