Nissan Repair: 94 Sentra XE 1.6, coolant temperature sensor, stock thermostat

Question
My '94 Sentra 1.6 (218,000 miles) overheated on me.
So we replaced the thermostat with a ULTRASTAT from O'reilly's. (The one they recommended. Its 190 degree i believe?)  

It still runs on the HOT side of the gauge.
It does NOT go all the way up to HOT but its much higher on the gauge than the stock thermostat.
As i drive it, it gets to the high line on the temp gauge, then cools back down to just above the midline range, then heats back up and cools back down.

Is this just going to be the norm since the thermostat is a higher degree or is there something else i need to check?

Water flows through the system (radiator cap off with car running, you can see the water moving.)
I have normal power, no misses or sputtering, no leaks we can see, no smoke...

Any help you can provide would be great!

Thanks!
Amber

Answer
Hi! I don't believe is the thermostat. Any thermostat that opens before the coolant reaches 185 degrees, it is not recommended because it takes much longer for the engine to go into a closed loop mode or it will keep running on a open loop mode. There is a number of reasons that could cause the motor to overheat. Retarded timing for one, but since you mentioned that you have normal power etc, we rule that one out. Is this an air conditioned vehicle? Are the cooling fans operating properly? Is there anything that blocks the air flow through the radiator? Is the coolant temperature sensor working like it should? Since this vehicle has high mileage, it is probably a good idea to have the radiator rodded out because it is possible that hard water deposits have accumulated on the bottom and even in the engine block. (Never use straight water in the cooling system) I hope this helps and as always, I recommend to have a tech looking at the problem because hands on diagnosis it's better!