Reservoir and cap assemblies provide contained volumes for critical vehicle fluids, including brake fluid, windshield washer fluid, and coolant/antifreeze. These components are located within the engine bay and typically utilize molded polymers for chemical resistance and durability. Caps feature pressure-relief valves or integrated seals to maintain system integrity and prevent leakage or contamination. Reservoir construction incorporates level indicators or sensor mounting provisions for fluid monitoring. Material specifications adhere to OEM standards for fluid compatibility and temperature resistance, ensuring long-term performance and safety.