core plug blew out

[85rturbo]

I was driving my svo last Friday. I don't drive the car much but over the course of the past year ive put aprox 1100 miles on the freshly rebuilt engine. 
but just the other day I was driving home from work (which is aprox 32 miles one way) and a core plug blew out (center plug on the exhaust side). lucky for me I was less than 1/2 mile from my home.
 I was curious if anyone has experienced this before? I'm running arp head studs with a comectic mls headgasket. also I run a 185 deg thermostat and an esslinger aluminum water pump with the underdrive pulleys. the turbo is water cooled and I am not running a heater. I did inspect the block after I picked it up from the machine shop and the core plugs looked good as they did replace them during the service they performed. maybe just a random failure??? not sure but if anyone has experienced this before and have a possible reason why the input would be much appreciated. thanks in advance

[Stinger]

If there was nothing wrong with the plug/block then it typically means you have a headgasket leaking combustion pressure into the cooling system. Typically it will release out of the overflow before it blows out a plug though.

[85rturbo]

Thanks. I dont see much to tell on the headgasket..i pulled the head off because I suspected the same thing. But nothing real obvious. Hopefully it was just an anomaly