Advice pls

I own a M reg 2.5 TDI disco and yesterday i did the head gasket on it and used a steel gasket. I then took the car for a drive and everything was mint and had no probs after sorting heating out. Today i was on the motorway and the temp hit the red and couldnt stop for about a mile and when i did it had boiled over. Just wanting to know if there is a common problem with these heads cracking or is it just an air lock causing this ? Just want to be sure before i pull it back to bits



Thanks, john

theres a common problem with them cracking.........