The problem is... I cant get to the temp thermo. The ratiator is the way?

fitted to nissan pathfinders... what year ?

if you cant find the thermostatic fan sensor for sale
or on or near the base of the radiator

I would say engine cooling fan runs from the ECU

the dash temp sender will be close to the thermostat housing

hint
you can fit after market cooling fan ...
with just an on/ off switch

Newer vehicles have an ECT Engine Coolant Temperature sensor and it is at the ratiator.
Old vehicles had a temperature sensor screwed into the block.

there are two temperature devices one that signals the gage that is in the head . the other is in the thermo housing that controls fan and fuel mix

Might want to check the catalytic converter, if this clogs up the engine cant breath correctly causing it to overheat. My guess is your fuel mileage has been going down as well.

Bad radiator fan motor or bad relay under hood or bad temp sensor.

its under the car on the left side on bottom of ratiator if your looking at your car it will be on the right on the bottom. its always on the opposite side of the ratiator cap on the bottom

It could be the radiator fan motor if all sensors and relays have been changed.......unplug the coolant temperature sensor the fan should come on and stay on unless the motor is bad or it is not getting electrical current.

Radiator fan is supposed to start working after the temp reaches a certain limit. And it is supposed to run til the temp reaches a certain lower limit. So when you switch off the engine and walk off the fans must be running to cool the water to that lower limit. Unless you seen that it runs well past that and does not stop at all. Does it start running when you start the engine? And runs throughout the time the car is running, which it should not. The relay seems to be out. It is this relay that controls the running of the fan. or the temp gauge. If the temp gauge is giving wrong temp then the relay has to keep working. Please check both, the relay and before that the temp gauge.

Check to make sure your thermostat works right by monitoring the warming up of your engine. With a completely cold engine, start and run the engine for a few minutes, then put your hand on the top radiator hose to monitor if and when it gets warm as the thermostat opens more and more and note the gauge reading( if it works) the top radiator hose should be unbearably hot within 5-8 minutes. If the therm. opens right it should close right aswell, staying open a little while eventhough the radiator may have cooled may be what you are experiencing causing the rapid cooling and is nothing to worry about. The Hose should not get warm very soon after starting the engine. Regarding you gauge, lets take one step at a time, verify proper op. or the therm.

Definitely can be the radiator.... if not take second look at that head gasket look under cap for a creamish deposit, that one sign of coolant and oil mixing. Good Luck