The thermal performances of two loop heat pipes driven by capillary force (CF) and pumping force (PF) using R245a as working fluid were experimentally studied. The variations responsive to the adjustments of heating power, condenser cooling condition and flow rate of working fluid for the average Nusselt numbers of evaporator and condenser, the heat transmission networks, the total thermal resistances and the cooling power consumptions for the CF and PF loop heat pipes were comparatively examined. A selective set of experimental data demonstrated the improvements of thermal performance for the PF loop heat pipe due to the increased vapor-liquid circulation rates and the modified pressure drop characteristics along the loop. The dominant physics for the thermal performance improvements from the CF references were discussed. A set of empirical correlations that permitted the evaluation of the total thermal resistances of the PF loop were devised to assist the relevant engineering applications. Justified by the vanished start-up limit and the reductions of thermal resistance disclosed by the present preliminary study, the research focuses for the technology advancement of the forced convective loop heat pipe was recommended.