Mingson - fan clutch works like a charm from start of car to when it's running hot, i
I'm having the same problem on my '90 300e. At first I thought it was the front fans. They don't kick in until the car has reached 107c or above or if I'm running the A/C.
After reading hundreds of posts mostly form Larry Bible, Arthur Dalton, tkamiya and hassman. What I have learned and feel is our problem is the fan clutch.
An easy test that I learned form one of the members above is to let the car run until you reach operating temp. Watching the location of the fan, with the hood up, turn off the engine. If the fan continues to spin more than one rotation, you have a bad fan clutch. In my case, the fan spins about 20 times. The fan should only spin 1/4 or 1/2 of a turn at engine cut off. (normal operating temp)
I never suspected the fan because I saw it running all the time. But after reading more post after post I tested it and found it to be rotating 20 or more times at cut off.
After removing the fan, idleing for 10min AND DRIVING the car for about 2 or more miles with NO FAN and CLUTCH, the temp still reacted the same (110c).
Also, I thought that my Aux fans were not working because I could never here them. But they do work, try running your A/C parked, and watch the front fans, they should come on. They will also come on at a 107c or so.....
This is after I changed the cap, top fitting, tightened all coolant connections and changed the Tstat.
Water pump, air pump, Tstat and other stuff had been replaced by PO only 8 months ago. Even the fan clutch looks new. But still over heating.
After driving the car with no FAN and CLUTCH, I was able to feel the radiator and all was HOT!!!!. Ouch! So, I don't suspect the radiator to be the problem.
From your post, the only thing you have not clarified in detail to work is the fan clutch. Try the test and let us know!! You might even want to remove the fan and bring the car up to temp. Does it reach the same temp with or without the fan? Does the fan continue to spin after shut off? Remember, I drove mine without the fan and the temp acted the same. 110c + .