Two days ago while at an idle in traffic my radiator blew a 1"x4" hole in the plastic Reservoir. The radiator was only 2 years old because the original on had a crack in the upper hose neck.... I was suspicious why a whole would blow out like it did. So, as a matter of coarse I change the t-stat and flushed the engine.
After replacing the radiator, all was normal. The t-stat opened at or near the operationg temp..... I added the appropiate coolent as the air escaped, then all of a sudden the reservoir started fiercely "boiling" over..... Now I believe I've ran the car with the reservoir cap off before.... What else in the coolant could it be? Could the Water Pump be cutting out?

Happy Thanksgiving

Kevin