An experimental study is carried out to investigate the pressure distribution and thermal performance of gravity assisted heat pipe charged with different working fluids. Methanol, water and Mono-Ethylene-Glycol (MEG) are chosen as working fluids which have different boiling point, density and viscosity. An experimental test apparatus is designed and produced including three heat pipes that heat input on the evaporator section are provided by solar energy. Measurements are conducted on the heat pipe surface for pressure and temperature variations. Pure antifreeze is chosen as working fluid, due to its high boiling point, along with water and methanol which are widely used in thermosyphon type heat pipes. Heat pipes are put into parabolic focused vacuumed glass tube and operated by solar energy for 11 days in order to achieve high temperatures. Data taken from 06.30 to 18.30 is taken into consideration for experimental results. Experimental results are evaluated for two days as (i) sunny and (ii) cloudy days by choosing days with the highest and lowest solar radiation. (i) As for the sunny day, the highest storage water temperatures for methanol, water and antifreeze were 90.0°C, 83.5°C and 86.7°C and the pressure values were 6.7 bar, 1.6 bar and 1.9 bar respectively. (ii) And for the cloudy day, the respective values of temperature and pressure were measured as; 43.9°C, 39.3°C, 29.0°C, and 2.0 bar, 0.2 bar and -0.3 bar.