<div class="htmlview paragraph">The theoretical evaluation of the thermal fields in a cylinder liner of Reciprocating Internal Combustion Engines (I.C.E.) requires some attention due the characteristics of the real boundary conditions.</div> <div class="htmlview paragraph">For small engines, in fact, these conditions may strongly differ from an axisymmetrical state due to the influence of the thermofluodynamic disuniformities at the gas and, more importantly, at the cooling fluid side.</div> <div class="htmlview paragraph">The paper brings together an experimental research on the temperatures at the boundaries with a theoretical analysis on the three-dimensional thermal fields occurring on the liner of a small one cylinder spark ignition research engine operating up to 5000 RPM.</div> <div class="htmlview paragraph">The differences found in calculating the heat exchanged using an axisymmetric analysis with respect to the real situation demonstrate the importance of considering the disuniformitites that really occur under working conditions. To improve the degree of accuracy the calculation of the heat exchanged has been done considering the effect of the experimental temperature errors in each position of the measuring sensors.</div>