Hydraulic Fluid Analysis

When was the last time you changed the hydraulic fluid in your stabilizer system or integrated hydraulic system? If the answer is more than three years ago, are you using hydraulic oil analysis to check the condition of your hydraulic oil?

Unlike crankcase oil systems, hydraulic oil systems are “closed systems” that minimize or eliminate the introduction of contaminants into the oil. Hydraulic systems “breathe” through the reservoir vent cap to allow for the normal expansion and contraction of the oil. As long as the system is breathing clean air from the engine room and the vent cap is fitted with a proper filter, then contamination should not normally be a problem.

Perhaps the worst culprit of oil degradation, after contamination, is over-heating. Marine hydraulic systems may be keel cooled or raw water (or coolant) cooled systems through a heat exchanger. Any reduction in the cooling capacity of the heat exchanger (or keel cooler) will cause over-heating and breakdown of the hydraulic oil. Monitoring the hydraulic oil temperature of your system should be part of your routine engine room inspections when underway. An operating temperature above normal (“normal” varies but is usually less than 150°F) is cause for further inspection. Any temperature over 180°F will cause irreparable damage to the hydraulic fluid and is cause for immediate oil change.

Contaminated or otherwise degraded oil, like a change in viscosity, will accelerate the wear on pump vanes, seals, and other system components. Therefore, most marine hydraulic system manufacturers recommended oil changes every three years as well as annual filter changes (check MMS or your manufacturer’s recommendations specific to your system).

Can you go beyond three years? On my 40’ trawler, Commander, we are on our fifth year on the same oil, BUT, we religiously perform annual hydraulic oil analysis to check our oil’s condition. If you are uncertain about the condition of your hydraulic fluid visit the products section of our website and purchase a cost effective hydraulic oil analysis package that will give you confidence that your hydraulic oil is in good shape (or not!).

Posted in Condition Monitor.