Radiator

if you are only doing short journeys then this is not long enough for your car to get up to operating tempreture there for the water doesnt circulate around the entire engine properly but with the bottom of the rad being cold i would say there is a air lock in the system if you are not familiar on how to get rid of the air lock then i would take it out on a good run with out the filler bottle cap on and this will remove the air lock for then replace the cap and job done

do not go for a drive out with the cap removed