The Most Important Lubrication Inspection Abnormal Changes in Oil Level

Jim Fitch, Noria Corporation
Tags: lubrication programs

A sudden change in oil level, either up or down, is a telegraphed alert that something is wrong. And, this “something” could potentially be serious. Deferring maintenance or ignoring this alert could lead to a costly repair and longer downtime in the future. The frequent examination of quality oil level sight glasses by trained inspectors is a sound condition monitoring practice. Perhaps the most important of all lubrication-related inspections.

Whether oil goes up or down, any sudden change in the oil level requires troubleshooting in search of the cause and corrective action. Just adding more oil or removing excessive oil is an activity of treating the symptom, not the cause. True, some oil level changes are rather common and quickly understood. For instance, if oil goes sharply down, you might have a conspicuous leak (internal or external) that can be easily found and plugged.

Internal leakage occurs when a fluid has gone from one compartment to another. Leakage may be associated with seal failure or perhaps the wrong oil in use. Low viscosity oils leak faster than high viscosity oils. An abrupt chemical change in a lubricant can affects its interfacial tension which can increase the rate of leakage.

If the oil level goes up, this may be due to the introduction of new fluid. For example, perhaps someone added too much oil, or another fluid like a coolant or even fuel has entered the system, which has raised the oil level.

What do Changes in Oil Level Mean?

Oil Too High:

When oil levels rise above the acceptable range usually something new has been added, i.e., a new fluid. But there are other options too.

Oil Too Low:

This is usually caused by leakage, but there are other reasons.

Oil Too High or Too Low:

The following conditions can cause the oil level to appear to be too high or too low.

Two Level Gauges are Better than One

It is a good practice to have an oil level gauge on both sides of some centrifugal pumps. If the pump is not centered in the casing, the oil level will not read correctly in the sight glass due to oil movement by the bearing. However, if you have two level gauges, an average of the two readings will give a better estimated oil level.

Q: Which of these slight glasses is better for detecting fluid level for oils that are colorless (clear and transparent)? Which is better for detecting aeration and foam?

A: The answer is A for both questions. Sight glass A can be viewed from any angle and produces a large top oil surface. It uses a port that is centerline with the oil level in the sump. This allows foam and rising air to be instantly observed. Sight glasses B & C use ports positioned well below the oil level. Sight glasses mounted below the oil level will not effectively trap rising air and foam for visual inspection. Additionally, such columnar sight glasses require adequate ventilation.