[SoCal LS-L]

Ok didnt put the junk in my radiator, but noticed another thing...... I started the car with the radiator cap off, and the coolant proceeded to flow out of the top steadily for the first couple minutes I had the engine running. The coolant got really frothy after about 45 seconds, almost a foam consistency, before it was even warm. Is this a blown head gasket?? Most of my other vehicles in the past you could have the cap off when it was cool and the coolant would just flow under the cap hole, it wouldnt come out. My oil looks ok, no white or mayo looking stuff in it, but the coolant looks a little dirty. Does everyone elses do this, or am I blessed with a thousand plus dollar repair?