If the lower hose is cold it isn't circulating the coolant. It could be air locked or clogged. Take off cap run engine and keep a look in the radiator to see if the thermostat opens if it does check temp gauge and let it run with the cap off and see if the lower hose gets warm. If it doesn't something is probability clogged but if it does watch it and see if it overheats. If it doesn't put the cap on and watch gauge and check hose if it starts getting hot and the hose gets cooler it's air locked. I have seen them overheat because the overflow hose was clogged up and even found one where for whatever reason if you took the lid off the overflow tank it was fine but if you put the lid on it would stop the flow??? Drilled a hole in the overflow container and never had a problem again. Good luck. Mike