I'd like to know how Seagate substantiates its temperature specs for this drive.

See section 2.10 of the manual.

Momentus 5400.6 Product Manual - Momentus 5400.6 SATA:
http://www.seagate.com/staticfiles/supp ... 6%20(Wyatt)/100528359d.pdf

2.10.1 Ambient temperature

"Ambient temperature is defined as the temperature of the environment immediately surrounding the drive. Actual drive case temperature should not exceed 70°C (158°F) within the operating ambient conditions."

Operating: 0° to 60°C (32° to 140°F)
Nonoperating: –40° to 70°C (–40° to 158°F)

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