Lubricating oil compositions

1. An internal combustion engine crankcase lubricating oil composition comprising:

(A) a crankcase base oil of lubricating viscosity, in a major amount; and

(B) the following additives, in respective minor amounts:

(B1) a metal detergent system comprising one or more metal salts of one or more acidic organic compounds, which system has a metal ratio of no greater than 3, and which system constitutes the only metal detergent system in the lubricating oil composition;

(B2) at least one organic ashless friction modifier;

(B3) at least one oil-soluble molybdenum compound; and

(B4) at least one metal dihydrocarbyl dithiophosphate,

wherein the crankcase lubricating oil composition has a total base number, as measured according to ASTM D-2896, of no greater than 6.

2. A composition as claimed in claim 1 wherein the metal in (B1) is an alkaline earth metal.

3. A composition as claimed in claim 2 wherein (B1) consists of one or more calcium salicylates.

4. A composition as claimed in claim 1 wherein (B2) is an ester-based or amine-based aliphatic friction modifier or both.

5. A composition as claimed in claim 1 wherein (B3) is an organo-molybdenum compound.

6. A composition as claimed in claim 1 further comprising:

(B5) a first base capable of neutralizing fuel combustion acids in the composition to form, in solution in the composition, a salt or salts of the first base and the acids, which first base is displaceable from the salt or salts, at least in part, by a second base.

7. A composition as claimed in claim 6 as part of an internal combustion engine lubricating system that includes a second base immobilised in the lubricating system and capable of displacing the first base from the salt or salts, at least in part, to form and retain a salt or salts of the second base and the acid or acids so that first base thereby displaced enters the composition.

8. A method for enhancing the friction characteristics of an internal combustion engine crankcase lubricating oil composition having a total base number of no greater than 6 comprising:

adding an internal combustion engine crankcase lubricating oil composition comprising:

(A) a crankcase base oil of lubricating viscosity, in a major amount; and

(B) the following additives, in respective minor amounts:

(B1) a metal detergent system comprising one or more metal salts of one or more acidic organic compounds, which system has a metal ratio of no greater than 3, and which system constitutes the only metal detergent system in the lubricating oil composition;

(B2) at least one organic ashless friction modifier;

(B3) at least one oil-soluble molybdenum compound; and

(B4) at least one metal dihydrocarbyl dithiophosphate to an internal combustion engine.

9. A composition as claimed in claim 1 wherein said metal detergent system has a metal ratio of no greater than 2.

10. A composition as claimed in claim 9 wherein said metal detergent system has a metal ratio of no greater than 1.5.

11. A composition as claimed in claim 1 wherein the organo-molybdenum compound is a molybdenum dialkyl dithiocarbamate compound.

12. A method as claimed in claim 8 wherein said metal detergent system has a metal ratio of no greater than 2.

13. A method as claimed in claim 12 wherein said metal detergent system has a metal ratio of no greater than 1.5.

14. A composition as claimed in claim 11 wherein the molybdenum dialkyl dithiocarbamate compound is a dinuclear or a trinuclear molybdenum dialkyl dithiocarbamate compound.