Engineering Tip – Advice for Using Sight Glasses


When inspecting equipment oil levels or performing oil changes, pay attention to the sight glasses.  There have been cases where the sight glasses have been stained, thus giving an appearance of lube oil from a few feet away.  This false reading has resulted in lack of lubrication failures.  In the case of a liquid level gauge, remove the glass tube and clean it.  If the stain cannot be removed from the glass, replace it.  In emergency cases when a new liquid level gauge cannot be located, flip the glass tube and install the clean side down.

The image given below shows a sight glass which indicates discoloured gear oil.


 The image given below shows a perfect sight glass arrangement with clear oil level indication.


Thus Oil sight glasses provides a wealth of information including but not limited to

  1. Oil level,
  2. Oil Condition, and
  3. Contamination – color change.
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  1. Sir,
    I am a faculty here in Chennai, with Hindustan Institute of Maritime Training, I have to take class on bacterial growth on lubricating oil (all information related).
    Appreciate, if could throw some information,
    With best regards
    KR Chandramouli

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