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