Where is the Coolant Temperature Sensor located on a 91 Nissan Sentra?

I am trying to fix my sister in law's car and the problem I found was the Coolant /Water Temperature Sensor. I have seen pictures of it at the parts store and it shows that is somewhere close to the uper hose of the radiator but I can not find it. Can someone please help me with details or a picture if possible. I am not a mechanic so the mechanic lingo makes it even more difficult. Thank you much. (Serious answers please)