not an endorsement, just an example-

https://www.amazon.com/Thermometer-58%E2%84%89-1022%E2%84%89-Instant-Read-Non-Contact-Temperature/dp/B07KB4S9KJ/ref=asc_df_B07KB4S9KJ/?tag=hyprod-20&linkCode=df0&hvadid=564707962680&hvpos=&hvnetw=g&hvrand=11286549795268674386&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9011785&hvtargid=pla-1569543240433&psc=1

shoot the top hose and the thermostat housing, along with where the temp switch for the gauge screws in.

when the car is cold, does the fan spin or is there resistance? when hot and running should be a definite fan noise, better at 3000 rpm or so. hold your hand close to the engine and feel the breeze. drop to idle and still hot, breeze should drop off according to rpm. you should always feel some breeze when the clutch is hot and working. shut off and spin fan. waaay too much resistance to spinning, maybe just move a blade or so and that's it. any looser and the clutch isn't hot enough or the clutch is defective. had problems with chinese clutches and usually use just behr, sachs or oe. was there a more expensive behr available? could be a bargain line behr has now. behr part numbers would tell me.

lastly, make sure the entire core of the radiator has heat hot in the top, approx 15 degrees cooler at the lower hose. a new radiator should be fine, never seen a bad one out of the box, only leaky.

also, were radiator and clutch listed for "tropical" applications. a euro car may not have to capacity to cool off in the u.s. almost always different specs and parts for euros and u.s. cars. i would've tried 560sel numbers to see if they are different than what you found for yours.