If your radiator is vibrating like crazy and your coolant overflow bottle is full and boiling like crazy, then you're overheating. other signs include cracks in the radiator end caps (if they're the stock plastic peices of shit).
It was mostly by touch and experance. The upper rad hose was VERY firm letting me know the thermostat opned up but it also sucked up the coolant i put in the overflow. Things were extremly hot to the toch after letting it warm up after 15 minutes and then driving it arround the block twice. let it "cool" down and turned it off. after that the rad was low on coolant.
The radiator wasn't full so it sucked up the coolant that it had and its probly still not full, thats why it could have gotten a little hot. There is no need to let a car warm up unless you are going to go drive it hard when you take off also our turbos are coolant and oil cooled so they really don't need to be cooled down especially if you aren't driving hard. It just a waste of gas doing all that.