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Um. I think the answer is in your post.
The fan clutch doesn't do the main portion of the cooling. It's the electric aux fan that does the vast majority of the cooling when stationary.
When you are moving, it would be the air blowing to the radiator that cools the car.

Did you pull the codes? Any aux fan codes? Or just test if the aux fan functions by turning on the AC. AC fan should start within some time.
If it doesn't, your aux fan is dead.

Don't have access to ISTA right now, but at the temperature you are reporting right now, the aux fan should be working regardless of ambient temp.

Cheers,
Gabe

--- EDIT ---
Ok. No codes.. that's weird. But the test procedure should still be the same.
 

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It's the other way around. The fan clutch is the main fan at idle and low speeds. The aux fan is....auxiliary. Only kicks in when the fan clutch can't keep up and when AC is on.

What coolant are you using? And mix ratio?
Which thermostat did you install? It could possibly be defective. They usually fail open, but I've seen a couple fail closed and raise both temps like in your situation.
Might want to try doing a combustion leak test.
Oh I must have mistaken. Sorry for the wrong info.
105 rings a bell to me btw. The M62 thermostat is a 105 degree one. Maybe used the wrong thermostat?

- Gabe
 

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This all of a sudden turned into a technical thread and now I'm super confused.
Two very reliable sources of the forum is giving the complete opposite info 🤪

Anyways, I don't think the technicality is super important. To my knowledge, the list of thing that can cause overheating on this engine is not that long.
What's important is that Shafro and Sailor's diagnosis yields the same test procedure.

Cheers,
Gabe
 

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I've had a similar issue this year, but my aux fan does work. I can confirm Shady/others are correct in that the aux fan does more. While trying to diagnose, I drove the car for an entire day this fall (mid 60's F) without the mechanical fan installed. I had pretty much the same operating temps in slower speed driving. It gets into the low 90's C. I'm sure it would go higher if I kept idling and moving too slow to move enough air across the radiator.

Turns out my issue is the radiator, which I was suspecting even though it's only 7-8 years old. Not enough flow at low speed and idle in traffic. I had already removed it and cleaned debris at the end of summer. It helped a bit but now I have the smoking gun - the radiator started to distort - it expanded the core. Internal clogging is my guess.

Since you're going to replace the fan, you'll have a chance to review the radiator condition. If you're hitting over 100C, you might suspect more than just the aux fan. As you know, best to replace one thing at a time though.
Hmm. A soft failing radiator. I'll keep this in mind as my cooling system isn't quite as good.
 
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