Dodge Repair: 2002 Intrepid, radiator fluid, mechanical spring

Question
Recently my car was overheating and I put water in for a few days then I didn't have any more problems. I had one mechanic check it and he drained all the radiator fluid, put 2 gallons of anti-freeze in, ran it sitting for 1 hr then drove it for 1 hour. No problems, no leaks, etc. My husband drove it 150 miles the next day again with no problems. The next day it overheated again after going about 5 miles and when we put water in it was just pouring out. We took it to another mechanic today and they said the thermostat and gasket needed to be replaced.
My first question is why did it not do anything for the other mechanic? Second, the labor was incredulous because they said they had to take apart a great deal of the engine to reach the thermostat...is this true? Third, why did it run so well for 2+ weeks on mainly water and no sign of a leak? Finally, is this a common problem with this make and model? Thanks. ** It is a V6 3.5L FI

Answer
labor time is only 1.3 hours  so what ever the rate is times that. Well as far as the over heating  it could be a stuck thermostat and its a mechanical spring so it could act up just being metal. There could also be other issues  such as the fans not coming on as well.I live in the Atlanta area I would be glad to look at it for u.