Prevent Sludge and Varnish with Proper Oil Flushes and Changes

Prevent Sludge and Varnish with proper Oil Flushes and Changes

Waiting too long for an oil flush and change out can lead to operational issues that arise from the formation of sludge and/or varnish in the system.  These issues include clogging filters, sticking valves (or other close-tolerance moving parts), coated heat exchangers which cause reduced cooling efficiency, and varnish build-up on bearings.

                A proper cleaning/flush of the system at change out is important since residual degradation products left in the system can cause rapid deterioration of critical properties (such as demulsibility) of the new oil.

                The use of a flushing oil as an intermediate step is typically done for one or two reasons:

  • To aid the transition from one fluid type to another
  • To allow for the addition of a cleaner that removes deposits like varnish, lacquer, and sludge. 

                Simply circulating oil through the system at design flow will do very little to address any deposited varnish. In addition, the amount of soluble varnish in the fluid that may be removed depends wholly on the type of purification and the time taken to perform the flush.  If needed, TestOil can conduct a Varnish Potential Analysis.  

                Using a flushing oil that is the same as the machine oil eliminates the need for much of the varnish removal from the fluid, but will have only a very slow-acting effect on cleaning any contamination and varnish deposits from the system

                To remove varnish deposits from the system, typically a chemical must be added to the old fluid (and circulated), then the system is rinsed with a flushing fluid and a third charge of fluid is used as final fill. 

                For more information on working with TestOil for oil analysis and training visit Contact: 216-251-2510; [email protected].

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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