Use of a lubricating composition as a single fluid for lubricating at least three mechanisms of motor vehicles: the engine, the gearbox and the hydraulic system of the vehicle wherein the lubricating composition comprises at least 50% by weight based on the weight of the final composition of at least one oil of groups I to V and at least 5% by weight, based on the total weight of the lubricating composition of a mixture of at least two polymers having a difference of permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C of at least 25, and having a viscosity profile such that (a) at 100°C after the Bosch-30 cycles test according to the CEC-L-14-A-93 standard the viscosity of the final lubricating composition is in the range from 9.0 to 12.0 cSt for an oil initially of grade 30, or else the viscosity of the final lubricating composition is in the range from 12.0 to 15.0 cSt for an oil initially of grade 40, and (b) at 100°C after the KRL-20 hours test according to the CEC-L-45-A-99 standard the viscosity of the lubricating composition is in the range from 8.5 to 11.0 cSt for an oil initially of grade 30 or 40, and (c) at 40°C after the KRL-3 hours test, according to the CEC-L-45-A-99 standard with the test duration reduced to 3 hours, the viscosity of the lubricating composition is in the range from 41 to 51 cSt for an oil initially of grade 30 or 40, the grades of oil being defined according to the SAE J 300 classification, and wherein said mixture comprises at least two different polymers of type "A", "B", or "C", the polymers of the mixture differing from one another in that they belong to a separate range of permanent shear stability index (PSSI) such that: - the polymers of type "A" have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C less than or equal to 40, - the polymers of type "B" have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C, between 40 and 65 exclusive; - the polymers of type "C" have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C greater than or equal to 65, and wherein the polymers of the mixture are selected from viscosity improving type polymers which are selected from the group consisting of poly-alpha-olefins with a kinematic viscosity at 100°C greater than 90 cSt, poly-isobutenes, polymeric esters, olefinic copolymers, homopolymers or copolymers of styrene, of butadiene or of isoprene, polymethacrylates, and optionally from among pour point improving polymers which are selected from polymethacrylates. (a) at 100°C after the Bosch-30 cycles test according to the CEC-L-14-A-93 standard the viscosity of the final lubricating composition is in the range from 9.0 to 12.0 cSt for an oil initially of grade 30, or else the viscosity of the final lubricating composition is in the range from 12.0 to 15.0 cSt for an oil initially of grade 40, and (b) at 100°C after the KRL-20 hours test according to the CEC-L-45-A-99 standard the viscosity of the lubricating composition is in the range from 8.5 to 11.0 cSt for an oil initially of grade 30 or 40, and (c) at 40°C after the KRL-3 hours test, according to the CEC-L-45-A-99 standard with the test duration reduced to 3 hours, the viscosity of the lubricating composition is in the range from 41 to 51 cSt for an oil initially of grade 30 or 40, the grades of oil being defined according to the SAE J 300 classification, and - the polymers of type "A" have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C less than or equal to 40, - the polymers of type "B" have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C, between 40 and 65 exclusive; - the polymers of type "C" have a permanent shear stability index (PSSI), measured after the standardized KRL 20 hours test at 100°C greater than or equal to 65, and