Take the coolant cap off (when the motor is cool) start it up and see if you can smell a fuel smell in the water - if so = a blown head gasket. If that is what it is don't ignore it - as the car can suck coolant into the engine as it cools down.
I rebuilt my BMW M5 engine which blew a head gasket at a race track earlier this year. My first full engine rebuild - not too hard to do if you follow the book.