Cooling problems

My friend has a 2002 Ranger with approximately 73,000
miles. It is the entry level model, no bells or whistles.
Has a 2.3 liter, 5-speed tranny, 2-wheel drive.
Question is: it has developed an overflow problem
at the radiator fill tank. After noticing the coolant level
being extremely low, I filled it back to the correct
level and drove the truck to my place for an oil change
and minor service. Upon arriving I noticed coolant
leaking onto the ground and upon further inspection,
saw a small crack in the fill tank. Also the coolant was
bubbling from the small hose that feeds into the flow
hose leading to the engine.
I checked the temp gauge, and was indicating the temp
was normal.
Could this be the early signs of a thermostat failure, or
worse water pump?
I am a real hands on guy, x-military mechanic, worked
at a garage for a while, and have always serviced
and repaired all my own toys, with the technology
on todays vehicles, without the proper tools and
equipment it gets more difficult to know what the
problems are, so any advice would be appreciated.
Thanks for your time.
Ray!