Abstract: A lubricating oil composition having an excellent sludge formation inhibiting effect and being suitable for use as an engine oil is provided. The lubricating oil composition includes: a lubricating base oil, (A) 0.5 to 20% by mass of acylated bissuccinimide, (B) 0.05 to 0.3% by mass of zinc dithiophosphate in terms of the phosphorus content, and (C) 0.5 to 4.0% by mass of metallic detergent in terms of the sulfated ash content, based on the total mass of the composition.

Abstract: A lubricating oil composition comprises (A) a base oil, (B) a 3-methyl-5-tert-butyl-4-hydroxyphenyl substituted fatty acid ester in an amount of 0.1-5 percent by mass and (C) an auxiliary component, said auxiliary component being one member of the group of (a) a nitrogen-containing compound in an amount of 0.001-1 percent by mass, (b) a sulfur and/or phosphorus-containing compound in an amount of 0.1-5.0 percent by mass or (c) a phenolic compound in an amount of 0.1-5.0 percent by mass. This composition features the combination with a base oil of these specified components whereby there is provided synergistic effect conducive to inhibition or prevention of both oxidation and sludge formation while in use under elevated temperature conditions over extended periods of time.

Abstract: A lubricating oil composition which comprises one or more base oils of the group consisting of (A) a mineral oil having a kinematic viscosity of 5-200 m.sup.2 /s at 40.degree. C. and an aromatics content of less than 15 percent by weight, (B) an olefinic polymer of 2-16 carbon atoms or its hydride having a number-average molecular weight of 250-4,000, and (C) an alkylbenzene having 1-4 alkyl groups of 1-40 carbon atoms and a total carbon number of said alkyl groups in the range of 6-40, said base oil or oils being blended with a 3-methyl-5-tert-butyl-4-hydroxyphenyl-substituted fatty acid ester in an amount of 0.1-5.0 percent by weight based on total composition. The inventive lubricant composition having such a base oil in combination with the specified fatty acid ester provides a synergistic effect conducive to inhibition or prevention of both oxidation and sludge formation while in use under elevated temperature conditions over extended periods of time.

Abstract: The present invention provides a lubricating oil composition which comprises in combination with a base oil:(A) a 3-methyl-5-tert-butyl-4-hydroxyphenyl substituted fatty ester of the formula ##STR1## where R.sup.1 is a C.sub.1 -C.sub.6 alkylene group, and R.sup.2 is a C.sub.1 -C.sub.24 alkyl or alkenyl group;(B) a N-p-alkylphenyl-.alpha.-naphthyl amine of the formula ##STR2## where R.sup.3 is a C.sub.1 -C.sub.6 alkyl group; and (C) a p,p'-dialkyldiphenyl amine of the formula ##STR3## where R.sup.4 and R.sub.5 each are a C.sub.1 -C.sub.16 alkyl group. The various components (A)-(C) as combined with a mineral or synthetic base oil are surprisingly conducive to both oxidation stability and sludge inhibiting performance under elevated temperature conditions over extended periods of service life.