An object of the present invention is to provide a dialkyl sulfide which can effectively form a metal sulfide film on a metal surface even in a low-temperature environment, has excellent storage stability, and is suitable as an extreme-pressure additive. The present invention provides a dialkyl sulfide represented by general formula (1) below (in the formula, R.sup.1 and R.sup.2 each independently represent an alkyl group, and n is an integer), wherein the content of a compound having an n value of 1 in the general formula (1) is 10.0% by mass or less relative to the total amount of compounds represented by the general formula (1) ##STR00001##

Provided are; a lubricating oil composition excellent in fuel saving performance, seizure resistance, wear resistance, fatigue lifetime and shear stability, which contains a base oil (A), an olefin polymer (B) having a number average molecular weight of 1,000 or more and 12,000 or less, and a specific sulfur compound (C) and wherein the content of all sulfur atoms based on the total amount of the composition is 1.2% by mass or more and 2.5% by mass or less; and a lubrication method using the lubricating oil composition.

A lubricating oil composition comprising at least 50 percent by mass, based on the mass of the composition of an oil of lubricating viscosity and 0.01 to 25 percent by mass, based on the mass of the composition of a polymer comprising units (a) and one or both units (b) and (c):

N(COR.sup.1)(CH.sub.2).sub.x(a)

NH(CH.sub.2).sub.y(b)

N(CH.sub.2CH.sub.2-k(CH.sub.3).sub.kCOOR.sup.2)(CH.sub.2).sub.z (c) where the total number (n) of units (a), (b) and (c) is an integer between 4 and 500; wherein x, y and z are independently 2 or 3; wherein k is zero or 1. The polymer shows good solubility in the lubricating oil and provides friction modification. A method of synthesising a polymer is also disclosed.

An antioxidant package composition including a combination of: (i) at least one hindered phenolic antioxidant, and (ii) at least one polyether sulphide; a lubricant composition including: (a) the antioxidant package composition and (b) at least one base oil; a process for preparing the antioxidant package composition; and a process for preparing the lubricant composition.

Provided is a grease composition for a magnet clutch of an automobile, including: a base oil; and a thickener, wherein the composition contains 5% by mass or more of a sulfur content in terms of sulfur element relative to a total mass of the composition.

Lubricant compositions comprising a base oil, one or more antioxidants selected from a group consisting of N--naphthyl-N-phenylamine antioxidants and diphenylamine antioxidants; and a sulfur-containing additive comprising up to seven carbon atoms exhibit outstanding oxidative stability and non-corrosion properties. The N--naphthyl-N-phenylamine antioxidants plus diphenylamine antioxidants in total may be present from about 0.2 wt % to about 0.8 wt %, based on the total weight of the lubricant composition. The sulfur provided by the sulfur-containing additive may be present from about 50 ppm to about 1000 ppm by weight, based on the total weight of the lubricant composition.

An object of the present invention is to provide a dialkyl sulfide which can effectively form a metal sulfide film on a metal surface even in a low-temperature environment, has excellent storage stability, and is suitable as an extreme-pressure additive. The present invention provides a dialkyl sulfide represented by general formula (1) below (in the formula, R.sup.1 and R.sup.2 each independently represent an alkyl group, and n is an integer), wherein the content of a compound having an n value of 1 in the general formula (1) is 10.0% by mass or less relative to the total amount of compounds represented by the general formula (1)

##STR00001##

Provided is a grease composition which contains (A) a mixed base oil containing (A1) a low-viscosity base oil having a kinematic viscosity at 40 C. of 10 to 50 mm.sup.2/s and (A2) a high-viscosity base oil having a kinematic viscosity at 40 C. of 200 to 700 mm.sup.2/s, (B) a lithium-based thickener and (C) a polymer having a kinematic viscosity at 100 C. of 1,000 to 100,000 mm.sup.2/s, and has an apparent viscosity at 10 C., as measured according to JIS K2220:2013 and at a shear rate of 10 s.sup.1, of 50 to 250 mPa.Math.s. The grease composition is excellent in pumpability and is also excellent in wear resistance under poor lubrication conditions.

The invention provides a method of lubricating a compression-ignition internal combustion engine with a maximum laden mass over 2,700 kg comprising supplying to the engine a lubricating composition comprising: an oil of lubricating viscosity, a 300 TBN or higher alkaline earth metal sulphonate detergent having a metal ratio of 10 to 40, 0.1 wt % to 4 wt % of a borated polyisobutylene succinimide dispersant, wherein the polyisobutylene from which the borated polyisobutylene succinimide is derived has a number average molecular weight of 550 to 1150, and 0.1 wt % to 6 wt % of a polyisobutylene succinimide, wherein the polyisobutylene from which polyisobutylene succinimide is derived has a number average molecular weight of 1550 to 2500, 0 wt % to 0.2 wt % of a phenolic based detergent, wherein the total amount of soap delivered by the alkaline earth metal sulphonates (typically calcium sulphonate) is 0.4 to 1 wt % of the lubricating composition, and wherein the lubricating composition has a sulphated ash content of not more than 1.5 wt %.

A gun oil composition adapted specifically for the needs and requirements of modern firearms. The gun oil composition improves lubricity and gun performance under normal and extreme heat and pressure, minimizes and largely prevents the build-up of carbon and debris fouling on metal and non-metal components of the firearm, and substantially reduces cleaning time, while providing increased protection against environmental components such as dust, dirt and rust. The gun oil composition can include a base oil having at least a high viscosity index, an oil having at least a medium viscosity index with a detergent additive, a low viscosity penetrating oil, and a sulfurized ester.