A hydraulic circuit (1) associated with an internal combustion engine (M) comprising a main cooling circuit (2) of the engine (M) provided with a circulation pump (4) for a cooling fluid, and an auxiliary preheating circuit (3) branched from the main circuit (2); the pump (4) is a rotary volumetric pump dimensioned so as to generate, at least during a warm-up transient of the engine (M), a flow rate greater than that required for the cooling of the engine (M); at least one fraction of the flow rate generated by the pump is sent to the auxiliary circuit (3) where it recovers heat from a fluid (23; 26) at higher temperature, such as the exhaust gases and/or the supercharging compressed air of the engine (M), and gives it to a fluid (24) at lower temperature, such as for example the engine oil or the passenger compartment air.