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!

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Current fleet:

1985 Mercedes-Benz 280TE - Waiting for heart surgery.

1985 Mercedes-Benz 300TDT - Rear ended 23 September 2016 and now looking for a new home.

1979 Mercedes-Benz 300TD - Parted out.

1964 Volkswgen Beetle - Vater's since September 1968 and undergoing a restoration.

1971 Volkswagen Sunroof Squareback with F.I. - in need of full restoration.

1971 Volkswagen Squareback automatic with F.I. - Vacationing with her caretaker until he is in better health.