I don't see the need. Modern BMW diesels (like the M57) already manage coolant, oil, charge-air, and emissions temperatures as a system. Thermostat operation and coolant temperature are part of a larger overall cooling strategy involving fueling, EGR control, radiator airflow, fan control, and regeneration logic, rather than being governed solely by a fixed-temperature thermostat.

- I see a 10-15 °C coolant increase during regeneration on these coldest winter day, which tells me airflow and heat rejection are functioning as designed.

-I’ve seen oil temperature overshoot on another modern diesel when airflow was restricted - coolant looked fine, oil didn’t.

- Heater output is warming up within ~0.1 mile and fully comfortable by ~1 mile, and fully hot within 5 miles even on the coolest days, which indicates normal warm-up behavior.

Partial radiator blocking may (surely does) help older mechanical diesels, but on modern emissions-controlled engines it can upset oil, charge-air, EGT, and fan strategies without improving warm-up. If coolant temps are stable and regen behavior is normal, blocking airflow isn’t fixing a problem — it’s overriding the system.

In my case, the cooling system behavior matches design intent. Regenerations occur normally and raise coolant temperature into the ~90-94 °C range (exactly the same as in tge summer on the hottest days), cabin heat comes on very quickly even in extreme cold, fuel consumption is normal for conditions, and DPF soot/ash modeling remains stable with no regen issues. This behavior has been consistent for ~60k and the ~130k miles before that, with no under-temp faults. This indicates to me the overall cooling and thermal strategy is functioning as intended, even though steady-state cruise temps are lower in deep winter.

I do not and have never blocked my radiator. I'm not sure what function or performance it's supposed to improve in my case.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim