Coolant Overflowing?

I have a stock '69 Nova with a 307 and a TH350. Today, I warmed it up for about 5-7 minutes and drove down to the gas station to fill it up for tomorrow. It's about 1 mile round trip. About 10 minutes or so after I got home, I noticed some coolant on the driveway. It made a spot about 9-10" in diameter and it's only 48 degrees outside. The upper radiator hose was rock hard and hot and the lower radiator hose was cool and soft. The water pump and themostat (180 degree unit) are only about 5 months old. Could the themostat be bad? Is the radiator plugged? It's the stock 3-core and has never been rodded out and I've had the car for 8 years. Thanks for any help.

That's odd that the upper hose would be hot, because that's the return hose (to the radiator). Maybe your radiator IS plugged. Since you have a thermostat, drain the radiator, disconnect both hoses at the radiator and try running water through it. If you didn't have a thermostat, you could just remove the radiator cap and start it up to see if the coolant is flowing. If the radiator is plugged up, depending on where you live, it may be cheaper to just replace the radiator.