by Drew D. Troyer

The most basic form of care is routine inspection. Inspections should be purposeful and systematic, employing checklists that clearly define non-conformance for each of the applicable conditions. Here’s a checklist for inspecting the health of oil-lubricated electric motors.

As I’ve previously suggested, I prefer inspection checklists that employ simple “yes” or “no” answers (e.g. lube oil pressure is between 22 and 24 psi — yes or no). The non-conforming condition should always be either yes or no to avoid confusion associated with the changing polarity of questions.  

1) Level: The most basic inspection for an oil-lubricated electric motor ensures that the oil is at the appropriate levels in the sump for bath, and ring and collar lubricated motors, and in the tank for circulating oil systems. A level indicator or bull’s-eye is sufficient. If the level is low, the technician should adjust the level and record the approximate volume of oil required to restore the sump or tank to its appropriate level. The tech should note abnormal oil darkening, which can indicate thermal or oxidative failure, as well as haziness or cloudiness, which might suggest water
contamination or excessive aeration.

2) Vent breather condition: If the tank or sump employs a vent filter to exclude contamination (which it should), check it periodically to ensure the breather isn’t full or saturated (for desiccant type breathers). Ideally, the vent breather is equipped with a vacuum indicator that alerts the technician that the element requires replacement. Desiccant changes color when it becomes saturated, which alerts the technician to service the element.

3) BS&W: Bath, and ring and collar lubricated motors may come with a bottom sediment and water (BS&W) bowl to collect water, sludge and debris. A simple inspection here alerts the technician to abnormal thermal and oxidative lube failure, water contamination and aggravated wear debris generation. Most of the devices come with a needle gauge so water can be cleared while the tech seeks the cause of ingress.

4) Ring and collar operation: Most motors are equipped with an inspection port to ensure that rings and collars are effectively slinging lubricant to the bearings. For this inspection, the technician looks for evidence of excessive aeration or foaming. Likewise, he or she checks the gasket on the inspection port and services it if required.

5) Fill cap: Inspect the fill cap to ensure it’s securely in place. It shouldn’t be removed, though, unless it’s necessary to change the oil or level. When removed, inspect it to ensure that its gasket or seal is in good order. Service it as needed.

6) Pressure gauge: For circulating oil systems, routinely check the oil pressure to the motor bearings. Loss of pressure could indicate a leak or diminished volumetric efficiency of the lube oil pump.

7) Temperature: Check the operating temperature each time the motor is inspected. Do this with a dedicated temperature gauge, non-contact thermometer or thermography camera. The camera is the most expensive and time-consuming, but in the hands of a skilled technician, it provides useful information.

8) Pressure differential indicator: For motors with forced circulation lubrication, filters are typically employed in-line or in a kidney loop configuration. Routinely inspect the pressure differential (psid) indicator or gauge and change the filter as required. If the filter has been in service for an unusually long period with no movement in the differential pressure, there’s a good chance the element isn’t working properly. Replace the element and inspect the used one. If the problem is chronic, contact the filter supplier.

9) Magnetic chip collector: The motor can be equipped with a magnetic chip collector or magnetic drain plug. Inspect the collector for abnormal accumulation of wear debris. Perform this inspection when the motor isn’t operating to avoid damage resulting from loss of lubricant upon removal of the plug.

10) Leakage: Record evidence of abnormal oil leakage out of the bearing, which may indicate the seals are worn and require replacement.

11) Flow: For circulating systems, confirm flow to the bearings, either visually or with a metering device.

12) Constant level oiler: Verify that the constant level oil is filled to the appropriate level and that, if it’s adjustable, it’s done so properly. If the constant level oiler fails to maintain the right level, its adjustment device may be shot, installed incorrectly or installed on the wrong side of the sump. The motor bearings should turn in the direction of the constant level oiler to reduce the risk that a vacuum will disrupt the oiler’s hydraulic lock and result in overfilling the bearing’s sump.

Drew Troyer is the senior editor of Machinery Lubrication Magazine . If you have a lubrication or oil analysis question, contact Coach Troyer at or e-mail . 

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