The heater heats the air by passing it over an exchanger filled with coolant diverted from the engine. Think of it as a mini radiator.

 

I have an oil temp gauge on my car, and i freak if my oil gets over 200. My daily driving in stop and go traffic sets up right around 180, driving over 45 mph is 145, and tracking it approaches 200. 260 is ridiculous. the only thing you can do is send mass emails to nissan and see if they will do something about it.