180 Thermostat

From what I understand, the warping is more from the inconsistency, as the hottest spots of the heads would be even LESS-effectively cooled than they are normally ineffectively cooled, with giant portions covered by hot vapor blankets, and thus being allowed to skyrocket far above 260 degrees in temperature in those localized locations, unlike the cooler parts of the heads, which would be far cooler and thus the temperature gradient would cause expansion differentials, which would warp the heads.

Aluminum melts at 660 degrees celsius, aka 1220 or so fahrenheit. The localized super-hot-spots are the enemy, as they cause thermal expansion out of line with the cooler parts of the head, thus the warpage. Aluminum heads tolerate 1000° EGT's on turbo engines, but are adequately and consistently cooled, so they survive.