i got my car the other day from a place about 40 mins away from my home and on the way back i called at my mates to sow them the new car , i kept the car ticking over to cool down even tho i was ony doing an honest 65-70 on the motorway , after about 2 miniutes there was a pop and alot of steam escaping from under the bonnet , on closer inspection the plastic had seperated from the metal on the radiator , the car is now back with the dealer i bought it off but has anyone any ideas of what could have caused this .

the car is a wrx sti ra classic
the temp guage was not high and the fans where not running afaik as i could not hear them , the engine runs smooth no bogging or lumpynss , the oil is clean , i just dont want it doing it again tbh