Described herein is an ashless oil additive, comprising at least one diazabicyclo or triazabicyclo compound. Also described is a composition comprising an engine oil mixed with an oil additive, wherein the oil additive comprises at least one diazabicyclo or triazabicyclo compound. Further described is a method for boosting the total base number (TBN) of an engine oil composition, comprising adding an oil additive to said engine oil composition, wherein the oil additive comprises at least one diazabicyclo or triazabicyclo compound.

A method for extending performance or service life of a lubricating oil in an engine or other mechanical component lubricated with the lubricating oil by using as the lubricating oil a formulated oil. The formulated oil has a composition including a lubricating oil base stock as a major component, and at least one microencapsulated lubricating oil additive, as a minor component. The at least one microencapsulated lubricating oil additive includes an encapsulating material (e.g., polymeric matrix) and a core material (e.g., at least one lubricating oil additive) encapsulated by the encapsulating material. A method of improving solubility, compatibility and/or dispersion of lubricating oil additives in a lubricating oil base stock. A method for controlling release of a lubricating oil additive into a lubricating oil. A lubricating oil having a composition including a lubricating oil base stock as a major component, and at least one microencapsulated lubricating oil additive, as a minor component.

A lubricating oil composition, containing a base oil (A), an aromatic carboxylic acid ester having one or more hydroxyl groups (B), and a sulfur-based antioxidant (C). A content of phosphorus atoms is 0.06% by mass or less, based on a total amount of the lubricating oil composition, and a sulfated ash content is 0.6% by mass or less, based on the total amount of the lubricating oil composition.

A lubricating oil composition for a gas engine containing: a base oil (A), at least one overbased calcium detergent (B) selected from the group consisting of calcium salicylate (B1) and calcium phenate (B2), alkenyl succinimide (C), and a hindered amine-based antioxidant (D), where the content (X) of calcium atoms derived from the component (B) is less than 0.090% by mass based on the total amount of the lubricating oil composition; the content (Y) of calcium carbonate contained in the component (B) is 0.060% by mass or more based on the total amount of the lubricating oil composition; the content of boron atoms derived from the component (C) is less than 0.020% by mass based on the total amount of the lubricating oil composition, and the content of the component (D) is more than 0.20% by mass based on the total amount of the lubricating oil composition.

Disclosed in certain embodiments is a lubricating oil composition comprising an antioxidant polymer (e.g., oligomer) composition comprising repeat units of diphenylamine monomers of formula I

##STR00001## wherein R is H, C.sub.1-C.sub.18 alkyl, C.sub.2-C.sub.18 alkenyl, C.sub.2-C.sub.18 alkynyl, C(O)C.sub.1-C.sub.18 alkyl, C(O)aryl and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently H or a linear or branched C.sub.1-C.sub.18 alkyl, C.sub.1-C.sub.18 alkoxy, C.sub.1-C.sub.18 alkylamino, C.sub.1-C.sub.18 dialkylamino, C.sub.1-C.sub.18 alkylthio, C.sub.2-C.sub.18 alkenyl, C.sub.2-C.sub.18 alkynyl or C.sub.7-C.sub.21 aralkyl and wherein the number average molecular weight (Mn) of the polymer composition is from about 350 g/mol to about 5000 g/mol.

Disclosed is a method of treating a used hydrocarbon lubricant of ISO Viscosity Grade 46 or higher comprising oxidation products that adversely affect lubricant performance. The hydrocarbon lubricant has a Group II hydrocarbon oil or Group III hydrocarbon oil, optionally one or more lubricant additives, and an amount of varnish. The hydrocarbon lubricant is free of zinc-containing additives. The method comprises adding to the used hydrocarbon lubricant from about 2 percent by weight to about 20 percent by weight of a polyhydroxy polypropylene oxide homopolymer that has a hydroxyl number of from about 12 mg KOH/g to about 58 mg KOH/g as measured according to ASTM D4274.

Methods are provided for in-situ detection of varnish and/or deposit precursors in a lubricant in a lubricating environment. An electrostatic accumulator can be used within a lubricating environment to enhance accumulation of varnish and/or deposit precursors on portions of the electrostatic accumulator. The deposits accumulated on the electrostatic accumulator can then be characterized in-situ. The potential difference across portions of the electrostatic accumulator can cause an enhanced rate of deposit accumulation on the electrostatic accumulator, which can facilitate characterization of the tendency of a lubricant to accumulate deposits in the lubricating environment.

Disclosed are solvency enhancer compositions, for example, as additives to lubricating oils and as formulated in lubricating oil compositions and associated methods of preparation and use thereof. The compositions and methods can dissolve at least one of oxidation products and other organic polar compounds, due to lubricant degradation, formed and suspended in oil compositions including adding an effective amount of a solvency enhancer to the oils, wherein the solvency enhancer includes Guerbet alcohols. Further described are methods for dissolving organic deposits in an oil system including adding an effective amount of a solvency enhancer to the oil system, wherein the solvency enhancer includes Guerbet alcohols. Also provided are methods for preventing sludge and varnish formation in in-service oils including adding an effective amount of a solvency enhancer to the oils, wherein the solvency enhancer includes Guerbet alcohols.

Disclosed is a method of treating a used hydrocarbon lubricant of ISO Viscosity Grade 46 or higher comprising oxidation products that adversely affect lubricant performance. The hydrocarbon lubricant has a Group II hydrocarbon oil or Group III hydrocarbon oil, optionally one or more lubricant additives, and an amount of varnish. The hydrocarbon lubricant is free of zinc-containing additives. The method comprises adding to the used hydrocarbon lubricant from about 2 percent by weight to about 20 percent by weight of a polyhydroxy polypropylene oxide homopolymer that has a hydroxyl number of from about 12 mg KOH/g to about 58 mg KOH/g as measured according to ASTM D4274.

An oil additive includes a hydrotalcite-like compound, and a radical trapping agent having a melting point of 130 C. or higher.