Slang for oil that looks like a creamy milkshake because water is emulsified into it, well past the point the oil can dissolve. In gearboxes and hydraulics it comes from washdown, condensation through open breathers or a leaking cooler; in engines a tan, mayonnaise-like sludge under the filler cap points to coolant or condensation. Milky oil loses film strength, rusts parts and strips additives.
Sight glass on the mixer gearbox is pure milkshake, somebody's been hosing down the seals again.
Let a hazy sample stand first: haze from entrained air clears on its own within minutes, while water haze stays until the sample is warmed.
Also heard as
- milky oil
- mayo
- mayonnaise
Related terms
Demulsibility
How quickly an oil sheds water and settles into clean layers after being churned with it.
Karl Fischer titration
Chemical titration that measures water in oil down to about 10 parts per million.
Crackle test
Quick screen for water in oil: put a drop on a hot plate and listen for crackling.
Desiccant breather
Vent filter packed with drying beads that cleans and dries the air a gearbox or tank breathes in.