Fuel economy is a major challenge for the automotive industry. A key way to improve lubricant fuel efficiency is by using polymers as viscosity index improvers to maximise the viscosity index of the lubricants. The viscosity index of automotive lubricants has an upper limit of around 250 because usage of high treat rates can lead to shear stability and flash point issues. To overcome this, the concept of two phase lubricants was reported in former literature but the practical application had not been examined. In this paper, the practical application with an additional ability to control viscosity and separation temperature simultaneously of a two phase lubricant is reported. It is possible to formulate a two phase lubricant with mineral or synthetic base oil and polyalkylene glycol to achieve viscosity index of 500 and keeping the properties of shear stability and flash point on a competitive level as of commercial single phase lubricants. Also, there is little evidence of issues with the lubrication properties. It was shown that additions of Di-isononyl adipate acting as a control element simultaneously control the viscosity and separating temperature of the two phase lubricants.
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