Abstract: A hydraulic exsiccate device lessens the presence of or prevents water vapor from entering the fluid reservoir of hydraulic machines which helps to reduce or eliminate damage to hydraulic systems used in environments such as boating, utilities, construction, manufacturing, fishing, industrial, marine, agriculture, military, mining, and so on. The hydraulic exsiccate device eliminates hydraulic reservoir fill caps, and in their place, the hydraulic exsiccate device is used as a cover fitting for closing the fluid reservoir (configured to conduct hydraulic fluid in the hydraulic systems) which operates to lessen the presence of or prevent water vapor from entering the fluid reservoir.