Most of us are aware that it is important to consider viscosity when selecting a grease. Another concern should be the base or thickener. Many thickeners are not compatible, such as lithium complex and bentone. When combined, the bases soften, and the lubricating oil pools and drops away from the bearing. Both may have the same NLGI designation, VI, work stability, dropping point, Timken OK load, etc.

They both may be listed as general- purpose grease. Don't be fooled into thinking they are the same. Noncompatible greases will contribute to lubrication failure in bearings. Check a base thickener compatibility chart to know if the grease you intend to use is compatible with what is in a new or existing machine. (Randy Widick, Vibration Specialist, Alcoa Inc.)

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One of the most common questions I'm asked when teaching lubrication courses is "are synthetics any good?" Oftentimes, the basis for this is question is a specific machine or group of machines, where a conversion from mineral to synthetic has either recently occurred, or is being planned. In doing so, the questioner is looking for validation of a decision that he or she has made, or advice on whether such a change is warranted for machines currently using a conventional mineral-based lubricant.

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"I've received 15W40 oil and the label on the drums read "Date refilled" (implying that they were reused drums) 6/6/2006. Am I running a risk with the TBN settling to bottom and if so will strongly shaking the drums incorporate the TBN package back into the oil in the drums? Do drums like these suffer settlement of TBN package and therefore lose some or a large amount of additive package protection?"

Generally speaking, the use of reconditioned drums is not recommended due to the difficulty of cleaning and the potential for contamination. However, additive drop out is no more or less likely in a reconditioned drum versus a new drum.

This motor oil is only one year old and the calcium (and possibly magnesium) detergent additive package in the oil that provides the oil with its Base Number (BN) should not have settled out (assuming that there has not been any significant water contamination enter the drum).

But, I have seen some situations in the past when some motor oil additive settlement had occurred. This was likely due to some additive in the oil being in such a high concentration that the oil became over-saturated with the additive at the storage temperature that the additive dropped out. Cold storage temperatures are the highest risk. So, it can happen.

Bottom line - I don't like to see any additive dropping out of solution from the oil. If you have reason to believe that additive has settled out, I would discuss it with the oil manufacturer's tech support staff. If you have reason to believe that water has entered the oil drum, take a bottom sample and have it tested for water (by co-distillation Karl Fischer method). Also, you could take a sample of the older oil from the top drum region and compare its spectrographic element analysis (Ca, Mg, Zn, P) against a known good sample of the same oil and check for element (additive) drop out (stratification).

Strong agitation might reincorporate the additive back into solution in the oil, at least temporarily, but the benefit may not be worth the risk to your equipment. However, if the oil has been grossly contaminated with water, any settled additive along with water at the bottom of the drum will not likely be brought back into solution by agitation

Bob Scott, Noria Corporation

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