Condition Monitoring for Hydraulic Fluid: Testing the Oil and Additives


Today’s hydraulic oils and their additives are fairly stable, but that doesn’t mean they will stay that way forever—they still need regular testing by an oil analysis lab for a number of factors, including additive depletion. 

                According to TestOil Field/Data Analyst Matt McMahon, who has been in this business for two decades, there are three primary additive classes for hydraulic fluids: antiwear additives; defoamers, and anti-oxidants.

                “Major lubricant formulators are adept at putting together a quality hydraulic fluid, but additives still deplete eventually,” he explains. “Once that starts to happen, you tend to see hydraulic systems developing operational issues. We can, in some cases, test the additive level and, in other cases, we can look for symptoms of additive depletion.”

                For hydraulic oils, Matt recommends the following tests:  

                While most of today’s hydraulic fluids should have some type of defoamer, there is a limit as to how much air entrainment is too much for even the most robust defoamer. According to Matt, it wouldn’t be unusual for a customer to report seeing foam during operation—i.e. oozing out of the vents in the hydraulic system—necessitating a foam test (ASTM D892). Matt also said that every now and then someone will ask for a varnish/RULER test for hydraulic fluid—especially if they notice things like sticking valves.

                Hydraulic systems work under tight tolerances and high pressure. As time goes on, hydraulic fluids are expected provide greater protection under harsher conditions. Given all this, accurate fluid testing is key to the longevity of the fluid and the equipment itself.

                For more information on working with TestOil for hydraulic oil analysis and maintenance training visit Contact: 216-251-2510;

About TestOil

With more than 30 years of experience in the oil analysis industry, TestOil focuses exclusively on assisting industrial facilities with reducing maintenance costs and avoiding unexpected downtime through oil analysis program implementation. As industry experts in diagnosing oil-related issues in equipment such as turbines, hydraulics, gearboxes, pumps, compressors and diesel generators, TestOil provides customers with a guarantee of same-day turnaround on all routine testing. With in-house, certified training professionals, TestOil offers lubrication and oil analysis training, private onsite training, certification training and exams, and educational webinars. For more information on partnering with TestOil on oil analysis programs or training opportunities visit

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