hello guys

I have a situation where samples from compressor bearing oil seal drain point mostly dropped its viscocity from ori ref viscocity.

What does this means? As far as i know, the viscocity of used oil will be more viscose so will increase the viscocity value. And i am wondering more since the oil does not content much water, only viscocity drop.

Appreciate any comments during festive day
Thanks!

My reaction is the same as yours. I would expect aging to result in viscosity increase. Viscosity decrease would suggest contamination by water or coolant etc or possibly by mixing incompatible oils.

There is a little different spin given in this article:
http://www.oilanalysis.com/art...ookgroup=OilAnalysis

If you look down at table 5 (near the bottom of the page) they suggest the following possible reasons for viscosity decrease:

• 1 - Contamination by a volatile substance
  
• 2 - Breakdown of VI improver additive (particularly noticeable in transmissions filled with a multigrade)
  
• 3 - General breakdown of the oil

1 is as expected.

2 I'm not sure. If we consider a typical operating band 40C to 100C, I'd expect the VI improvers bring up the viscosity at 100C or bring down the viscosity at 40C. Breakdown of VI improvers would then decrease the viscosity at 100C and increase the viscosity at 40C. I think 40C is the normalizing temperautre used for trending. My first guess is I would expect breakdown of VI improvers to cause an increase in viscosity at 40C. Maybe I am missing something.

3 is surprising to me since I associate things with aging like: sludging and varnish and loss of more volatile components of the oil... all of which I associate with increased viscosity. It's hard for me to understand why aging/oxidation could result in decrease in viscosity.

This message has been edited. Last edited by: electricpete,

I agree with your comments,

the viscosity fall might come from shearing forces in the oil, that either break high viscosity components into lighter fractions (like VI improvers), or sometimes low quality polyolesters POE decompose in lower viscosity components. Check what is the type of oil in the safety data sheet.
Oils tend first to lose viscosity with aging before the viscosity start to climb again.

I have seen this in oil lubricated seals for hydrogen recycle and wet gas compressors. Product contamination of the seal oil causes dilution. In addition to degrading lubricant the possibility exists to go above LEL in the reservoir.