Patent ID: 7678746

Claim:
A method for lubricating a marine diesel internal combustion engine, comprising supplying thereto a lubricant comprising: (a). at least about 3 weight percent of an overbased sulphonate detergent with a metal ratio of about 12.5:1 to about 40:1; (b). at least about 1.5 weight percent of a sulphur containing phenate detergent with a metal ratio of not more than about 3, wherein the sulphur containing phenate detergent has a TBN of about 50 to about 190; and (c). an oil of lubricating viscosity, (d) 0 wt % to 10 wt % of at least one optional performance additive selected from the group consisting of metal deactivators, dispersants, antioxidants, antiwear agents, corrosion inhibitors, antiscuffing agents, extreme pressure agents, foam inhibitors, demulsifiers, friction modifiers, viscosity modifiers, pour point depressants and mixtures thereof, wherein the sulphur containing phenate contains oligomers of hydrocarbyl phenol with at least about 50 wt % of said oligomers in the form of the tetramer or higher oligomers, wherein the total amount of (a) and (b) is 4.5 wt %, to 35 wt %, wherein the specific amounts of component (a) and component (b) are present such that component (a) delivers at least 60% of the TBN supplied by the detergents (a) and (b), and wherein the (TBN) of the composition is 30 or higher.