FYI my daughter's 98 Sentra GA1.6L thermostat stuck, I replaced it. Not as hard as some of the posters griped about it, but it is a little hard to get to (on the firewall-side of the engine, held on by three bolts, one of which you can't really see). I found that some of the parts stores were only stocking the 180 deg thermostat and calling that OEM replacement; but the FSM called for the 170 deg. I'd make sure you get the 170 deg thermostat, it made a difference for me (always runs a notch below 1/2-way mark on temp gauge). I think I remember that the thermostat had a little bleeder-thing built into it, that should be positioned at the top when you install it. It's function is to prevent air pockets from forming. Also, check the radiator hoses/clamps, I found that the OEM clamps had slow leak/crud buildup around them. I removed them, wire-brushed the dried-coolant off, and replaced the clamps with the worm-gear/screw-on type. No more leaks!
Oh, check the top of the alternator for evidence of dried-up coolant, that's what clued me into having the slow leak.
And I don't know if the overheat is causing the power-loss, but maybe if you clear up one problem the other will go away...
Hope this helps.
Last edited by skeeter123; Oct 1st, 2010 at 11:45 AM.