Fluctuating temps like that are a good reason to yank the radiator and have it rodded out and if need replaced. Good time to replace the thermostat with a new Nissan factory one.
Your 86 is almost 20 years old! Lots of accumulated corrosion inside can cause all sorts of hassles. A new two row radiator core will cost you a couple hundred bucks, and a new fan clutch about 50. Believe me, it is worth the effort.
By the way, you have to remove the front bumper to get the radiator off, not difficult and very necessary.