Topped oil , coolant etc prior to a 400 mile journey to Glasgow yesterday - driving around today the coolant light came on after only driving half a mile or so - had to top up with 1L of water and then drove 4/5 miles and purchased some radweld plus and added this in - have done a couple of 4-5 mile journeys since and coolant level doesn’t seem to have dropped - due to drive the 400 mile return journey tomorrow but bit concerned about this happening on the motorway - any suggestions or advice appreciated