98 ZX2 P0125 code temp gauge not working

[highrolla7]

hello all
So I recently purchased a 98 zx2 auto with 50000 miles. Drove it home and temp gauge didnt rise up like it should. Then it did, then dropped back down. The heater only throws out "hot" air when the temp gauge is where it is supposed to be. So anyway, lately it has been working (i added more coolant) and everythings working great.( for about 30 miles or so) Now all of sudden- 4th straight day the temp gauge doesnt move at all!! Not even a little bit-if it does, its just a little bit-never above the C mark. The heater still throws out "warm" air, but not hot. THe check engine came on and so I had it checked and its P0125 (Insuffiecient coolant temperature for closed loop operation). So, at Autozone, I purchased a new thermostat and sending unit. Am I on the right path here? Is there anything else I should look out for? THe temp gauge does move a little, but never above C mark and I know that cant be right. When the temp gauge is where it was supposed to be, it would get hot in there with the heater on, now its just a "lukewarm" heat. Any help would be great guys!! Thanks, T. J.

[AltecZX2]

i'd say thermo

closed loop means driving over 3000RPM

[highrolla7]

okay, I was just reading somewhere here that somebody had bad luck with autozone thermo's. Maybe I'll take it back and get an OEM thermo and hope that works. thanks