Abstract: A residual fuel oil is improved in dispersion stability when a large amount of sludge is contained therein and comprises (1) a thermal cracking oil, (2) a diluent and (3) a dispersant selected from the group consisting of (A) an imidazoline derivative containing a hydrocarbon group having 7 to 23 carbon atoms, (B) a hydrolysis product of (A), (C) a reaction product of an aliphatic acid having 8 to 22 carbon atoms and a polyalkylenepolyamine having 4 to 6 amino groups, (D) a monoamine containing a hydrocarbon group having 8 to 22 carbon atoms, (E) a polyamine containing a hydrocarbon group having 8 to 22 carbon atoms, (F) an etheramine having a long chain hydrocarbon group, (G) a phosphate having a long chain hydrocarbon group, (H) a salt of (G), (I) a dithiophosphate and (J) a salt of (I).

Abstract: A lubricating oil composition containing esters constituted with glycerol, fatty acid and boric acid, which esters having carboxylic acid residue, glycerol residue and boric acid residue at a specific proportion.The proportion for the carboxylic acid residue and glycerol residue ranges 0-2.0 mols and 1.5-2.0 mols respectively per unit mol of a boric acid residue, and the glycerol residue is 1.2 mols or more based on 1 mol of the carboxylic acid residue.Lubricating oil additives according to the invention have almost no corrosion property in bearing portions, and do not form any solid film on themselves when allowed to stand in the air.

Abstract: A method of preparing an overbased lubricating oil additive comprising introducing carbon dioxide into a mixture containing (1) an oil-soluble organic acid or a metal salt thereof, which acid or salt includes a hydrocarbon group having 8 to 150 carbon atoms, and (2) an alkaline earth metal compound selected from the group consisting of oxides or hydroxides of alkaline earth metals, at a temperature of higher than about 100.degree. C, in a reaction medium of a lubricating oil, in the presence of a reaction accelerator comprising a dihydric alcohol, a phenol compound and elemental sulfur, thereby to effect complete carbonation; and thereafter removing all of the volatile components contained in the reaction product.