Yeah, there are both the Haynes and Chilton manuals available for the model years that include the 98 Pathfinder. I bought the Haynes and it seems to be pretty good. It is a little more focused on the 2.4L and 3.5L engines that came out during those years, but it is still pretty good. It is my understanding from reading a post a number of weeks ago that the Haynes and Chilton manuals are exactly the same now as Haynes bought out Chilton a couple of years ago. I got mine off Barnes and Noble for $22. Good luck!
Look for the lower Rad hose, follow it up toward the engine, it will go into a steel pipe that is a few inches long, then turn rubber again, at the end of it is the T-stat housing. but they usually don't go bad that often unless it was replaced with an aftermarket one. odds are you have a coolant leak somewhere.