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Fuel consumption after a cold start remains one of the major goal of carmakers. The high friction losses due to a low oil temperature are the main sources of the consumption excess during the warm-up. To improve the prediction of these losses, the local oil temperature in friction areas must be well represented. The local equilibrium temperature depends both on the heat flux generated by friction and on the oil flow rate. The aim of this work is to represent the thermo-hydraulic behavior of oil loops during the warm-up of a cold start. Oil pump efficiency is evaluated considering Poiseuille and Couette flow contributions on the leaks of the pump. Computed results are validated on results gained on a test bed. The hydraulic behavior of bearings is modeled from a theoretical approach. The effects of bearing deformation are rendered by a global elasticity coefficient calibrated from results in a previous paper.

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.