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Dictionary of Lubricant Terms


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MASS SPECTROMETER - apparatus for rapid quantitative and qualitative analysis of hydrocarbon compounds in a petroleum sample. It utilizes the principle of accelerating molecules in a circular path in an electrical field. The compounds are separated by centrifugal force, with the molecules having a greater mass (weight) being thrown to the outer periphery of the path. Quantitative measurements are accomplished by use of either a photographic plate or electronic determination of the relative proportions of each type of particle of a given mass.

MEAN HERTZ LOAD - See load wear index.

MERCAPTAN - any of a generic series of malodorous, toxic sulfur compounds occurring in crude oil. Mercaptans are removed from most petroleum products by refining, but may be added to natural gas and LPG in very low concentrations to give a distinctive warning odor.

MERIT RATING - closed scale with 10 being the best possible rating. See engine deposits.

MIDDLE DISTILLATE - See distillate.

MINERAL OIL - any petroleum oil, as contrasted to animal or vegetable oils. Also, a highly refined petroleum distillate, or white oil, used medicinally as a laxative.

MINERAL SEAL OIL - distillation fraction between kerosene and gas oil, widely used as a solvent in gas absorption processes, as a lubricant for the rolling of metal foil, and as a base oil in many specialty formulations. Mineral seal oil takes its name - not from any sealing function - but from the fact that it originally replaced oil derived from seal blubber for use as an illuminant for signal lamps and lighthouses.

MISCIBLE - capable of being mixed in any concentration without separation of phases; e.g., water and ethylalcohol are miscible.

MIST LUBRICATION - See oil mist lubrication.

MOLYBDENUM DISULFIDE - a black, lustrous powder (MoS2) that serves as a dry-film lubricant in certain high-temperature and high-vacuum applications. It is also used in the form of pastes to prevent scoring when assembling press-fit parts, and as an additive to impart residual lubrication properties to oils and greases. Molybdenum disulfide is often called moly of molysulfide.

MONOMER - See polymer.

MOTOR OCTANE NUMBER - See octane number.

MOTOR OIL - See engine oil.

MULTI-GRADE OIL - engine oil that meets the requirements of more than one SAE (Society of Automotive Engineers) viscosity grade classification, and may therefore be suitable for use over a wider-temperature range than a single-grade oil. Multi-grade oils have two viscosity grade numbers indicating their lowest and highest classification, e.g., SAE 10W40. The lower grade number indicates the relative fluidity of the oil in cold weather for easy starting and immediate oil flow. The higher grade number indicates the relative viscosity of the oil at high operating temperatures for adequate wear protection. The “W” means “winter” grade. Multi-grade oils generally contain viscosity improvers that reduce the tendency of an oil to lose viscosity, or thin out at high temperatures.

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