Cooling and Overclocking the Raspberry Pi 4 and 5: Heatsinks, Fans, and Safe Clock Limits

Both the Pi 4 and Pi 5 will quietly throttle themselves under sustained load if you don't manage heat, and both will also give up real, repeatable performance if you're willing to add cooling and nudge the clocks. This guide covers what throttling actually looks like, the cooling options worth using, and the overclock settings that are broadly considered safe versus the ones that start eating into stability and silicon longevity.

How to Tell You're Being Throttled

Raspberry Pi OS throttles based on a die temperature threshold, not a fixed clock table, so a Pi under load can silently lose 20-30% of its performance without any obvious error message. Check the throttle state directly:

vcgencmd get_throttled BitMeaning 0x1Under-voltage detected (right now) 0x2ARM frequency capped (right now) 0x4Currently throttled 0x10000Under-voltage has occurred since boot 0x20000Frequency capping has occurred since boot 0x40000Throttling has occurred since boot

A result of 0x0 is clean. Anything with the 0x1/0x50000-range bits set means your power supply, not your cooling, is the actual problem — fix that first, since undervolting will make any thermal work pointless and can cause data corruption on SD cards or attached drives.

Cooling Options, Cheapest to Most Effective

• Passive heatsink only — fine for light, bursty loads (a Pi-hole, a simple sensor logger) but will throttle within minutes under sustained CPU load like compiling or video transcoding.
• Official Pi 5 Active Cooler — a small PWM-controlled fan and heatsink that clips onto the mounting holes and is thermally managed automatically by the firmware; this is the reference solution for the Pi 5 and works well.
• ICE Tower-style tower coolers — heat pipes plus a larger fan, popular for Pi 4 case mods; noticeably better sustained thermal headroom, at the cost of case compatibility and some fan noise.
• Passive aluminum cases (finned enclosure acting as one big heatsink) — good middle ground for a silent, always-on server that isn't under constant heavy compute load.

Whatever you use, thermal paste or pad quality between the SoC and the heatsink matters more than the cooler's size on a board this small — a poorly-seated stock pad is a common cause of surprisingly bad temperatures on an otherwise capable cooler.

Safe Overclocking: Pi 4

Overclock settings live in /boot/firmware/config.txt. Community-tested, broadly stable settings for a well-cooled Pi 4B:

over_voltage=6 arm_freq=2000 gpu_freq=750

Stock clock is 1500 MHz; 2000 MHz with a modest voltage bump is the commonly-cited stable ceiling for boards with active cooling. Pushing further into the 2100-2147 MHz range some enthusiasts run is silicon-lottery territory — it works on some boards and not others, and instability there tends to show up as filesystem corruption rather than a clean crash, which is the real risk.

Safe Overclocking: Pi 5

The Pi 5's BCM2712 has less headroom above its stock 2400 MHz than the Pi 4 had, and Raspberry Pi's own firmware already runs it fairly close to its practical ceiling. A modest, well-documented bump:

arm_freq=2800 over_voltage=4

with the official Active Cooler installed. Going meaningfully past this without exceptional cooling tends to hit the same thermal ceiling the stock clock was already designed around, so the real-world gain from Pi 5 overclocking is smaller than it was on the Pi 4 — cooling to prevent throttling under stock clocks is usually the higher-value project on this board.

Verifying Stability

Don't trust an overclock until you've stress tested it:

sudo apt install stress-ng stress-ng --cpu 4 --timeout 600s --metrics-brief vcgencmd measure_temp vcgencmd measure_clock arm

Run this for at least 10 minutes while watching temperature; if it climbs past roughly 80°C on the Pi 5 or 85°C on the Pi 4, back off the clock or improve cooling before calling the setting stable. Follow with a real workload for a day or two — a quiet crash or filesystem corruption days later is the actual failure mode to watch for, not an immediate stress-test failure.

Undervolting for Battery and Solar Projects

The same config.txt knobs work in reverse. For battery-powered or solar Pi builds (see this site's LoRa gateway and off-grid sensor projects), dropping arm_freq to 1000-1200 MHz and disabling unused peripherals (Bluetooth, HDMI output via tvservice -o, USB) trims idle power draw meaningfully without hurting most sensor-polling or logging workloads that spend most of their time waiting on I/O anyway.

Safety Notes

• Overclocking will not damage the board catastrophically if you keep voltage bumps modest, but it does void the "not overclocked" assumption in Raspberry Pi's own support guidance, and instability from a marginal overclock can silently corrupt an SD card or attached storage over time.
• Always pair any overclock with an adequate power supply — the official 27W USB-C supply for Pi 5, 5V/3A for Pi 4 — since undervoltage and overclock instability produce nearly identical symptoms and are easy to misdiagnose.
• Keep an eye on case ventilation generally, not just the heatsink; a well-cooled Pi inside a sealed enclosure with no airflow will still cook over time.

For most home-lab uses, the better return on effort is proper cooling at stock clocks rather than chasing an overclock — it eliminates throttling entirely, costs nothing in stability risk, and on the Pi 5 in particular closes most of the gap an overclock would have bought anyway.