Grease vs Oil Lubrication — How to Choose

Lubrication is the single largest factor in bearing life — well over half of all premature failures trace back to it.

When grease wins

• Speed factor (n × dm) below ~500,000
• Sealed-for-life designs
• Vertical shafts where oil drainage is awkward
• Re-greasing intervals measured in months or years

When oil wins

• High speed: gearbox-driven oil bath above 500,000 ndm; oil-mist or air-oil above 1,000,000
• High temperature where grease oxidises
• When swarf, coolant or process fluid must be flushed out

NLGI grade quick reference

Re-grease quantity (RGQ)

The textbook formula:

G = 0.005 × D × B

where G is grease in grams, D is outside diameter in mm, and B is bearing width in mm. Round up to the nearest 1 g and apply with a calibrated grease gun — over-greasing causes more failures than under-greasing.