Thermal convection has been modeled in a 3-D model box, in order to study the structure (diameter and temperature anomaly) of mantle plumes and their surface manifestation (topography, geoid anomaly, heat flow). In a previous study (the seminar on the 12th Nov 2003) the results of depth dependent models were presented. The comparison of that results and the characteristics of the real hotspots showed that the two most problematical parts of the models are the very high temperature anomaly of the plume and the high topographic anomaly above the plume. Hence this presentation focuses on the effect of temperature dependent viscosity on these parameters. The first steps of the started research are presented, applying weak temperature dependency and low Rayleigh numbers. To see separately these effects, depth and temperature dependent viscosity law was applied. The viscosity increases exponentially from the top to the bottom by a factor of 10 and 100, as in the previous models. The additional exponential temperature dependency has a factor of 2, 10 and 100. The investigated models have a surface Rayleigh number between 10^5 and 5*10^6. The temperature anomaly of the plume becomes lower by the addition of temperature dependency. The temperature of the ambient mantle increases when stronger temperature dependence assumed. The hot material has lower viscosity in temperature dependent models. This lower viscosity can not support so high topography, that's why the topography radically decreases by applying stronger temperature dependence.