sounds like your thermostat is stuck, assuming I read you post right...
I read your question as if you've replaced the waterpump, and something about replacing some coolant lines, but are not getting any coolant flow so you engine is overheating while the radiator and coolant lines stay cool to the touch. Sounds like either a major clog in the system or a stuck thermostat to me.
Be care-full my radiator blew up and burnt me. I replaced Radiator, thermostat, and water pump. Timing belt is in the way so I replaced it too. OK Now
you might want to check for a blown head gasket or a cracked head or block. espically if it loosing water out of the radiator with out leaking on the ground.
check your radiator. is it clean or does it need to be replaced? a simple cleaning cured my problem.
Contact Thermagasket @ 1-925-215-1211 and ask them. I had same problem with my 98 Northstar and they sold ma a part that takes 10 minutes to install using a knife/scissors and a screw driver. Stopped my car from overheating instantly. Northstar has built in problem, this fixes it.
check your fan clutch if its weak it will overheat
did you check the radiator or the head gasket?
Is the cooling fan[s] coming on? is the radiator full of coolant ?does the engine have a blown head gasket or cracked head? Why did it need a radiator?
dose the electric fan run if not check the relay if it runs check the water pump
You either have a cracked block, blown head gasket, or intake manifold gasket leaking coolant into the engine oil. You have bad problems.
Check the timing.
have the engine timing checked. if the timing is wrong the engine will overheat, are you loosing coolant?is the fan working, is the water pump working?
Radiator caps are pressure relief valves. They are rated at "pounds per square inch" and are designed to release some pressure from the radiator if it gets too high. If an engine overheats it can boil the coolant and this will cause the radiator cap to let out steam. Radiator caps DO lose their ability to regulate pressure and can release too soon. If the engine has not overheated, have the radiator cap tested and replaced as necessary.