Looking to Avoid Hydraulic System Failures?

From "Insider Secrets to Hydraulics"

When fluid moves from an area of high pressure to an area of low pressure without   performing useful work, heat is generated. This means that any component in   the hydraulic system that has abnormal, internal leakage will increase the heat   load on the system and can cause the system to overheat. This could be anything   from a cylinder that is leaking high-pressure fluid past its piston seal, to   an incorrectly adjusted relief valve. Any heat-generating components need to   be identified and changed-out.