FYI. I've owned my 1966 230Sl since 1977, enjoying every moment both driving and working on it, she's up to 260,000miles.
While it is a 230SL, the engine was blown and a 280SE/SL was installed before I bought it.
Overheating while in heavy traffic or while idling has been a regular occurrence. Usually rising from 180F to 200Fplus.
I had the radiator rebuilt with extra coils, fitted a coolant bypass at the fire wall and an additional oil cooler along with a pair of 12" electric fans, all in an effort to control this problem. All having minimal effect.
I stumbled into an artical dated around 2016 or 17 and cannot find its, source, advocating the Thermal Time Switch, located behind #6 spark plug, be removed and a coolant line run from the threaded opening, tapping into the upper, return, radiator hose.
This I did, fitting an extension to accommodate the TTS.
Since this conversion, my over heating has been resolved, normal summer running, the temperature remains steady from 180 to 185 degrees. while in heavy traffic or just sitting idling, the temperature remains within that range. Many thanks to that unknown person.
Two pictures attached, questions/comments welcome. Sorry second picture detail of TTS is obscured by an after market auxiliary coolant pump fitted, that I will eventually remove.