With the increasing efficiency of D.I. Diesel engines, the heat power needed to warm the passengers compartment becomes too low during the warm-up period. So the temperature increase of oil and water may be accelerate. This paper is devoted to the understanding of the phenomena involved in this process and their modeling.A diesel engine enclosed in a calorimeter is mounted on a test bench and largely instrumented. From the recorded data, the instantaneous energy balance is set up for different running conditions. Some general trends may be pointed out. During the first minute, 50% of the fuel energy is absorbed by the heat capacity of the heavy metallic components. This part progressively decreases to the benefit of heat transferred to the coolant. Furthermore, for increasing distance from the combustion chamber in the block, the rate of temperature rise decreases. Concerning the oil temperature evolution, it lags behind the water one.In order to find efficient and cheaper solutions for industrial development, a nodal model (lumped capacity method) of the engine thermal behavior is implemented and validated from the experimental data. It gives numerical results closed to the experimental ones on a wide range of operating conditions (until ¾ of maximum speed and ½ load). Then the model allows to evaluate the interest of competitive configurations to accelerate the warm-up such as: preheating of oil or water, reduction of the losses to ambient air, heat supply in coolant…The main result is that an important flux flows towards the lower part of the block due to its great mass and lower temperature.