Nissan Repair: Nissan Maxima 1999 thermostat, nissan maxima, temperature gauge

Question
First, thank you for answer related to blower resistor . I replaced in 10 min and everything fine.
Recently I noticed that it takes much longer for temperature gauge reach normal postion (around 9.0 clock position).Only after sitting in slow traffic needle goes there. On higher speed looks like needle goes down, however I have heat even when needle close to "C". Also idle RPM stays aroung 900 much longer.
I believ it is time to replace thermostat. My 1999 Maxima SE has 156K miles and I never replaced coolant.
What is involved in thermostat replacement beside coolant? Is it make sense to replace belt also.I prefer " do not fix if it works". How difficult to replace thermostat if I need it.
Thank you,

Answer
Jeff,

Go to Nissan and pick up a new thermostat.  It is the best deal going.  Nissan sells the thermostat with a new neck all together.  Be sure to get the gasket too.  Now remove the old one and replace it with the new one and you are good to go.  Be sure to change the coolant and go back wiht Prestone or the like 50/50 with distilled water.  Do not back flush the system with any pressure from a garden hose or you will blow the heater core.  Just drain and refill with the 50/50 mix.  Also, follow the bleed instructions to get the air out of the system.  If it were me I would be replacing the hoses soon anyway.