By Jim Fitch
Machinery Lubrication Magazine
The term “short-volume oil change” (SVOC) relates primarily to circulating oil systems. An SVOC occurs when an oil change (either scheduled or condition-based) only involves draining and refilling the oil in the system tank or sump. All or some significant portion of the oil remaining in the oil lines, hoses, bearings, pumps, filters, actuators, valves, heat exchangers, etc., is not changed. In other words, it is a partial oil change.
From a practical standpoint, when oil is drained from machines, there is always some residual amount that, at minimum, occludes to interior surfaces and becomes trapped in low regions, quiescent zones, and other nooks and crannies. For example, after an oil drain, diesel engines typically retain approximately 15 percent of their previous oil. When the engine is refilled with new oil, you end up with an 85-to-15 new-oil-to-used-oil blend.
The main concern with this practice is the influence the used oil has on the health of the blended new oil charge. If the used oil was low in volume and relatively healthy, the performance and life expediency of the new oil blend can be acceptable. Conversely, if the used oil was contaminated and/or heavily degraded from extended use, the performance and life expectancy of the new oil blend can be sharply affected. For instance, it takes less than 5 percent oxidized oil mixed with new oil to reduce the oxidation stability of the new oil by more than 90 percent.