Went to fill up with fuel locally (about 2.5 miles). Noticed when pulling in to the forecourt ,water temperature high - almost off the scale when stationary! Nose cone off, radiator and bottom hose stone cold, coolant level appeared to be OK in expansion/header tank. After engine cooled down, I took out the top plug from radiator, no coolant visible! Topped-up radiator, (approximately 1.5 lites) header tank still about half full. Ran the engine 'til warm and coolant now circulating (bottom hose now hot) and drove home. Water temperature normal on the drive home but coolant everywhere. With nose cone off, coolant was pouring out of the filler cap/valve. Once the engine cooled down header tank half full. Did I overfill or should I be looking for something else? Any advice please.