It is quite common for old lube oils to fail water separability test. How big of a concern it is? Well, it depends on the systems’ operational conditions, oil sump size (residing time of oil contaminated with water before it is pumped back into the system), and the rate of water ingression. If water ingression is relatively low (generated mostly by condensation and not coming from leaky coolers), than a low-flow off-line cellulose fiber filtration system hooked on the individual sump would keep the oil dry, and keep cleanliness in check. In addition, it is important to test oil frequently, which will enable you to detect presence of water as early as possible. At that point, a vacuum dehydrator comes pretty handy.
Certainly, you can buy base stock oil, but the question is – what for? There are no additives in it that are essential for R&O oils. Blending additives is a delicate process. You may not be able to achieve their proper balance, if adding them to you oil in your plant.
