Yesterday I was finishing a drive of about 80 miles when my heater quit blowing warm air (it's currently winter here). I noticed the temp gauge was at the red mark, so I pulled off the highway and stopped at a light. The engine immediately shut off when I stopped. I smelled antifreeze and the hood was steaming. I waited for it to cool down a little, then drove it the two blocks home.
There I noticed the coolant reservoir cap was popped open, there was hardly any coolant in the reservoir, but there was coolant all over the engine. I've been reading up on this and it sounds like it could be a few issues, one common one being a head gasket issue.
The thing is, the head gasket on my Subaru was replaced about 30k miles ago. (Now the car is at 144k). So, a relatively new HG.
Any help in diagnosing this would be great. Do I need to just do a coolant flush and burp?