Dell R740XD2 – Fan speed locked at 75–100% despite iDRAC/Bios settings

Hey all,

We’re having trouble getting the fan speed on our R740XD2s into a manageable range — it seems stuck between 75% and 100% for all fans, no matter what we do.

Hardware setup:

• Dell PowerEdge R740XD2

• 24 HDD's installed (30-35C)

• 3 × PCIe NVMe (Samsung P1725) (40C)

• 2 × 12-core Xeon Silver CPUs

• OS/BOOT: Flatcar

The problem:
When booting and running Flatcar, our fans automatically ramp - and stay - at:

• Fans 1–2: ~70–75% (14,400–14,500 RPM)

• Fans 3–6: ~88–100% (18,000–18,240 RPM)

This is drawing excessive power and increasing our electricity bill noticeably.

Thermal & cooling configuration:

• Thermal Profile Optimization: Minimum Power (Performance per Watt Optimized)

• Fan Speed Offset: Low

• Minimum Fan Speed in PWM: Default (37% PWM)

• PCIe Airflow Settings: Mostly disabled, except Slot 5 set to Automatic (Airflow Controlled)

• System Inlet Temp: 22 °C

• System Exhaust Temp: 35–36 °C

• Target Exhaust Temp Limit: 70 °C (Default)

Temperature readings (30 systems average):

• CPU1: 60-70 °C

• CPU2: 66-77 °C

• System Board Inlet: 22-23 °C

• System Board Exhaust: 35-37 °C

What’s odd:
If I install Ubuntu 22.04, run updates and load drivers (plus ipmitool), the fans immediately drop to a much more reasonable range (35–50%), while keeping CPU temps below 77 °C. This was without drives installed, perhaps that also affects airflow quite a lot.

What I’ve tried:

• Multiple racadm commands to set manual fan control - no avail.

• BIOS and iDRAC cooling settings (20+ combinations) - no avail.

• Low power mode (drops PWM slightly and saves ~30W — not enough)

Ideal target:

• CPU fans (1–2): 75–80%

• PCIe fans (3–6): 50–60% (no need for 88-100%)

• Controlled manually

Current status:

• Manual commands via iDRAC or IPMI have no effect under Flatcar

• Ubuntu works fine, so this seems related to how Flatcar interacts with Dell’s thermal management?

• Unknown PCIe NVMe drives may be influencing airflow logic, but I can’t get fine-grained control

Anyone have clues on how to:

1. Get manual fan control working in this setup, or

2. Stop the system from forcing such high fan speeds?

Screenshots from iDRAC attached for reference.

Thanks in advance — any insights would be greatly appreciated!