Help re: intermittent overheating

[Tbonem3]

I, personally, would replace everything at that mileage, esp an lsb of a pcar owner

[LSB4Me]

And there you have it folks. The use of logic and shame in equal measure by our friend T-Bone has landed me at full overhaul.

Good to know that a radiator would have likely solved my problem(s). Half measures be damned, as they say.

[heinzboehmer]

Mileage = 138k

Yeah if things are original, I would replace everything too at that mileage

[EthanolTurbo]

Yeah if things are original, I would replace everything too at that mileage

Me too. I just assume any E46 M3 that has 100-200k miles on it needs almost everything replaced that's a wear item unless noted otherwise.

[sapote]

After a decent testing period, I can say that the coolant temp starts to climb: (1) on hot days; (2) with the AC on; and (3) when the motor is being run harder—meaning, shifts at 5k+ or while under load (uphill). Another clue is that the coolant temp returns to the midpoint when turning the AC off. And yes, I can hear the aux fan doing its thing

A few thoughts.
1) If Elec fan was running which means the lower hose was hot. But this is possible only for a normal car, so double check by reach in and feel the lower hose to make sure it is indeed hot.
2) If the lower hose is hot, this means the Tstat opened properly and the WP works fine. Then the issue is the radiator doesn't exchange enough heat.

[kkkk]

I had this problem and hunted it down for ages
Go into the secret menu and press 19/7 to get the temps up for the coolant engine temp sensor and let me know what they are with and without AC on (+ ambiemt temps)

I changed
2 water pumps
1 radiator
Engine coolant temp sensor
radiator temp sensor
Clutch fan

Its a little better but still gets up to 93C with the AC on. and 88C without. When I pull the lower radiator hose sensor, it gets to 86-87C. This leads me to think its the aux fan or the aux fan module playing up