Erratic engine temperature on '81 300D
 

My engine temp is running consistently higher than normal. Usually it is around 80-90c and has always fluctuated a little while driving but currently the temp is at or above 100-110c consistently after warming up. In addition, the temp gauge is moving much more frequently as in dipping or jumping 10 degrees every few minutes.

The weather has warmed up recently (I live in SoCal) but I don't think this is the issue. This morning on my commute to work the temperature outside was in the high 60s low 70s and my engine temp was hovering above 100c (the notch above 80).

Coolant level is fine, no leaks. What's going on?

That's what I figured would be the first step, radiator flush + replace thermo. Thanks!