10. THERMAL MANAGEMENT

rev 3.3 re-baseline: this section was written for a 350W Z440 workstation — that machine is shelved. The in-truck brain is now the ~80W OptiPlex 5080 Micro, so the thermal problem shrank ~4×. Most of the stack below is now optional/insurance rather than mandatory. What remains mandatory is the software cutoff (a hot sealed cab still cooks any electronics, and LiFePO4 BMS limits matter more than the CPU).

An ~80W micro-PC in a hot cab is a modest thermal task (it was the build's hardest problem only when the brain was a 350W workstation). Layered, cheapest-first:

1. MOUNT smart — rear seat w/ airflow, or bed under cover (cooler, shaded)        [keep]
2. AC DUCT — flex duct from a cabin vent to the OptiPlex intake (~$30)            [optional now — 80W rarely needs it]
3. EXHAUST FAN — 12V fan pushes hot air out (~$20)                                [optional now]
4. THERMAL CUTOFF (code) — cab-temp sensor (ESP32) → auto-hibernate if cab >120°F or CPU >85°C  [KEEP — still mandatory]
5. TWO-TIER already helps — OptiPlex HIBERNATES during the hot parked hours (~2-5W, near-zero heat); ESP32 layer handles parked monitoring

Worst case (sealed hot cab, sun) = exactly when the OptiPlex is hibernating (~2-5W, near-zero heat). The remaining job is keeping it cool while DRIVING — easy at 80W with AC usually on; the duct + fan are cheap insurance, not requirements. The ~$5 cab-temp sensor + software cutoff is the part that actually matters (protects the cab electronics and respects the LiFePO4 heat limits noted in the power banner).