Glad,
I might be able to help here.
Managing the thermal loads (keeping stuff cool and keeping stuff warm and moving heat energy around) in any combat aircraft is quite a hard job. In stealth aircraft, it's harder because you have less freedom to scoop cold air in and dump hot air overboard. F-35 (all variants) therefore has had quite a challenge to achieve this under all and any conditions.
A standard technique is to use the fuel in the tanks as a heat sink to soak up excess heat. (You might have heard that one problem the Nimrod AWACS Mk3 never solved was excess heat buildup in the wing fuel tanks).
F-35 uses this technique, (as well as many others) but early on in the programme it was realised that at really extreme conditions (over 45 degrees C, heat soaked for many hours and warm fuel) there were corners of the flight envelope where the thermal management systems were having trouble coping.
The F-22 and B-2 had both had the same problem, and at the same locations - US air test establishments in the hot south west, e.g. Palmdale and Yuma. The solution was to arrange for chilled fuel to be made available for test flying to allow unrestricted operations. At no time was chilled fuel required for deployed operations.
Same for F-35. It used the legacy chilled fuel supplies to support test flying, but chilled fuel is not required for deployed ops. In any case, fuel from AAR platforms is usually cool, as is fuel from ships.
Hope this helps,
Best Regards as ever to all those working the logs and support stuff,
Engines