over heating problem on my 1.4 petrol 307

[johnson1988]

hi there just joined can any 1 help me??????? hi there can some 1 help me please!!! what it is i have just bought a 51 plate peugeot 307 1.4 petror about there weeks ago and everthing thing seemed fine but over the past week i had a msg flash up on the display sayin engine coolant temp to high then flashing stop but would olny do this wen the car is in traffic or moving slow. so i thought what could this be. so i asked my friend who knows a bit about cars he says its a temp sensor located at the right hand side of the egine so i have changed that and also changed the thermostat and i thought that was it and unfortunately it is still cumin up the same on the display. also i have checked the car is not losing any water either does any 1 no if there is another sensor or something what could be causeing this??? thanks for looking