Oil and fuel circuits in a turbine engine, the circuits including a main oil/fuel heat exchanger passing flows of oil and fuel for cooling the oil, an oil/air heat exchanger mounted in the oil circuit and having a flow of cooling air passing therethrough, a bypass pipe connected between an oil inlet and outlet of the oil/air heat exchanger, a valve for controlling passage of the oil flow through the bypass pipe and the oil/air heat exchanger, and a secondary oil/fuel heat exchanger mounted in the bypass pipe.