Sudden Jump to 120*C and Then Jumpy Needle

[Adriel]

Going down the freeway, think I hear something, check my gauges, and see coolant temperature is at about 120*C. Keep a real close eye as about right on and not in the red. I soon see it cool to just below (110*C?), then jumpy. When I go a short ways on surface streets and the needle really starts jumping and twitching. Once got near my home was now bumping into 120*C, but not going over. Let it idle to cool the turbocharger, but since don't have a shroud and was going a little up, shut down. I then look under the hood and find no obvious leaks; just got home from pressure washing the engine compartment. Any ideas?

Thank y'all for the help in advance!