Sounds like it could be a stuck thermostat. Maybe when changing the radiator hose, you lost some coolant, but didn't see it until it warmed up. Added coolant and it was back to normal. Not sure how you would have lost much coolant changing the upper hose. But then again, the new radiator cap now allowed you to pressurize the system, so the level in the tank would then drop. I'd grab a thermostat to be safe. It's right underneath the round metal piece that your upper hose connects to. Grab a gasket too. (O ring)
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2002 GT 5sp. 16x,xxx miles
Steeda Exhaust, C&L plenum, BBK Throttle Body, Steeda Underdrive, Steeda short throw, unknown stage clutch. Rear main leak. Compressor seal leak. Steeda lower control arms. good tires.