Hello my Brother in law has a 89 maxima 4DSC he has change the radiatior and cap when the car is driven for more that 2 hours non-stop the temperature fluctuate from the middle to all the way to the top of gauge.
and goes back down again.
2.) heater in the car set at 85 Deg. sometimes blows normal air and some time blows hot.
3.)If thermostat is jacked does it sometime work or just does not oper at all?
what do you guys think?

thank you

 

sounds like a thermostat

 

or just maybe the cooling system needs to be bled. the site below has very good instructions.
see: http://members.csinet.net/tisch/maxima/

 

I'm gonna second doing the 39" bleed first.
though it usually only affects heat output