Yesterday my 2000 volvo S40 began overheating rapidly when I came to a stop light. When I initially started the car that morning, the heat wasn't working, but the car was not overheating, nor was the check engine light on, or anything else abnormal that would indicate a problem. Pulling over immediately and popping the hood, i saw that anti-freeze was spewing out of the resevoir. I then refilled the tank with water, and was able to drive the car to my father (a mechanic) who lives approximately 15 miles from where i was at. During this time the heat still was not working, but the car did not overheat at any point during the drive. My father inspected the car and noted that the anti freeze was mixing with oil, but there was no white smoke emitting from the tail pipe, etc. Could this be anything besides a blown head gasket, such as a damaged tubo?