Sir yebo, i think you are right, because one time i really observed whats happening: before my trip--about 30min drive--i filled the coolant reservoir to the max level. after arrival, i checked the coolant reservoir and i saw that it was filled to the brim. i left it that way. I went back home late that day and checked again the reservoir, upon arrival, and found out that the coolant level was almost at the min level.

Sir yebo, thanks for the enlightenment. And for the other guys, thanks to you too for your comments and suggestions.