Method for preventing or reducing low speed pre-ignition while maintaining or improving cleanliness

A method for preventing or reducing low speed pre-ignition in a spark ignited internal combustion engine lubricated with a lubricating oil comprising the steps of:

• lubricating a spark ignited internal combustion engine with a lubricating oil comprising at least one lubricating oil base stock at from 70 to 78.1 wt. % based on the total weight of the lubricating oil, wherein the base stock is a blend of a Group III and a Group IV base oil and about 5 wt. % of a Group V base oil;
• and at least one dispersant at a loading to contribute from about 50 to 240 ppm of boron to the oil,
• wherein said at least one dispersant comprises a mixture of at least one borated dispersant comprising a borated polyisobutylene succinic anhydride/polyamine (PIBSA/PAM) at from about 0.6 to 2.8 wt. % of the oil and a non-borated dispersant comprising a PIBSA/PAM capped with ethylene carbonate or a polyisobutenyl bis-succinimide at from about 3.3 to 9.0 wt. % of the oil, wherein the boron to nitrogen ratio for the at least one dispersant is greater than or equal to about 0.05 to less than or equal to about 0.242 and at least one overbased calcium detergent at about 5.0 to 5.5 wt. % based on the total weight of the lubricating oil, wherein the at least one overbased calcium detergent comprises one or more calcium salicylate detergent having a Total Base Number (TBN) from about 70 to 200 with the proviso that the lubricating oil is free of elemental magnesium and essentially free of magnesium based detergent, wherein the other lubricating oil additives comprise from about 8.6 to 14.8 wt. % of the oil, and
• measuring the deposit control of the lubricating oil via the TEOST 33C (ASTM D6335) and the low speed pre-ignition (LSPI) of the spark ignited internal combustion engine lubricated with the lubricating oil via the Ford LSPI test,
• wherein the spark ignited internal combustion engine exhibits greater than 50% reduced low speed pre-ignition, based on normalized low speed pre-ignition (LSPI) counts per 25,000 engine cycles, engine operation at 2000 revolutions per minute (RPM) and brake mean effective pressure (BMEP) at 18 bar, as compared to low speed pre-ignition performance achieved in a spark ignited internal combustion engine using a lubricating oil that does not comprise the at least one borated dispersant, or a mixture of a boron-containing compound and a non-borated dispersant and the at least one overbased calcium detergent, and
• wherein the spark ignited internal combustion engine exhibits Ford LSPI test counts of less than or equal to 21, and
• wherein the deposit control is maintained or improved (TEOST 33C total deposits less than or equal to 34 mg) as compared to deposit control achieved using a lubricating oil not containing the at least one borated dispersant, or a mixture of a boron-containing compound and a non-borated dispersant and the at least one overbased calcium detergent.