Lubricating oil composition
A lubricating oil composition for a heavy duty diesel engine comprises a base oil, at least 0.6 mass % of an ash-free antioxidant and an overbased magnesium-containing detergent. The detergent provides greater than 0.05 mass % Mg based on the mass of the composition. Bore polishing in the engine is reduced for a given level of exhaust gas ash production.
1. A lubricating oil composition for a diesel engine, comprising the following components:
(a) a lubricating oil basestock of lubricating viscosity;
(b) an antioxidant component;
(c) a detergent component; and
optionally (d) one or more metal hydrocarbyl dithiophosphate compounds in an amount of from 0.0 to 1.8 mass % and/or (e) a calcium detergent compound;
wherein the antioxidant component (b) is selected from one or more ash-free aminic and/or sulfur-free phenolic compounds in an amount of at least 0.6 mass % up to 3.0 mass % based on the total mass of the composition; and the detergent component (c) is an overbased magnesium compound having a total base number (TBN) exceeding 350 mg/g KOH selected from one or more magnesium sulfonates, magnesium salicylates, and magnesium phenates and which provide the composition with greater than 0.05 mass % Mg based on the total mass of the composition, and wherein the sulfated ash content of the composition is at least 0.6 mass % to not more than 2.0 mass % as determined by ASTM D874.
2. The composition of claim 1 wherein the Mg content does not exceed 0.3 mass % based on the total mass of the composition.
3. The composition of claim 1 wherein the Mg content is at least 0.06 mass up to 0.15 mass % based on the total mass of the composition.
4. The composition of claim 1 comprising one or more dispersants.
5. The composition of claim 4 wherein the dispersant(s) include one or more nitrogen-containing dispersants.
6. The composition of claim 5 wherein the nitrogen content provided by the nitrogen-containing dispersant(s) is at least 0.07 mass % based on the total mass of the composition.
7. The composition of claim 6 wherein the nitrogen content provided by the nitrogen-containing dispersant(s) is in the range of from 0.07 to 0.25 mass %.
8. The composition of claim 1 wherein the antioxidant component(s) consist of ash-free antioxidant compound.
9. The composition of claim 1 having a sulfated ash content no lower than 0.8 mass %.
10. The composition of claim 9 having a sulfated ash content no lower than 1.0 mass %, and no greater than 1.6 mass %.
11. The composition of claim 10 having a sulfated ash content no lower than 1.0 mass %, and no greater than 1.5 mass %.
12. The composition of claim 1 wherein the amount of phosphorus provided by the metal hydrocarbyl dithiophosphate is in the range of from 0.05 to 0.20 mass % based on the total mass of the composition.
13. The composition of claim 1 wherein the detergent component (c) comprises salicylate detergent.