An oil heating system in a turbine engine such as an aircraft turbojet or turboprop main engines, or in an aircraft auxiliary power unit (APU). The turbine oil heating system includes a turbine engine oil circuit for conducting lubricating oil to the turbine engine, an electric starter generator oil circuit for conducting cooling oil from the electric starter generator, and an oil-to-oil heat exchanger connected with the engine oil circuit and connectable with the electric starter generator oil circuit, for transferring heat from the starter generator oil to the engine oil as to warm-up the engine oil during turbine engine motoring prior to actual starting sequence. A low cost and highly integrated system is therefore provided for reducing drag torque of a turbine engine prior to the starting phase.