hey, this morning i changed to coolant in my frst to a 50/50 coolant and antifreeze. the old coolant looked like it needed changeing so i changed it, however it was running ok, ie not overheating.

but now, if you run the car for 15 mins or so... the water justs get boiled and the engine gets mega hot..... even though the coolant level is sat on the maximun line and all the water hoses are sealed fine.
anyone know what the problem could be.....