I had similar problems. I decided to remove the stock mechanical fan as it drove me crazy when it sounds like a jet engine in front when booting it a bit. I installed a 12" fan in front of the stock 3 core radiator. Car started to run a litter hotter but still middle mark or just below it. When booting it or driving on the freeway it would climb to about 2/3 on the gauge and not drop at all unless the car is switched off so that the fan can cool down the non circulating water. I didn't get the core cleaned out yet and thermostat is brand new genuine nissan one.
So I put back the stock mechanical fan.

I still suspect my core is a bit blocked because is summer even the stock mechanical fan struggles to keep temp down and the electric fan kicks in to help it a bit. with them both the temp comes down and is ok but if mechanical fan is removed, not a chance the electric fan will do the job.