Perhaps my post was slightly misleading, there is no hottest or coldest fuel "end", the fuel temp is what it is and is largely uniform as it enters the FCOC, again remember that it's an oil cooler - not a fuel heater but you can take "benefit" from the hottest oil in raising fuel temps at what is evidently a critical point in the system, i.e the heater matrix end plate.
The fix that I mentioned is, in my opinion, little more than a sticking plaster, if the focus is to be an engine fuel system orientated fix then it should be focussed on getting a bit more heat to fuel in the FCOC loop, and as I have said previously this is normally achieved via the FMU spill return to LP rather than HP as in the T800.
However, in saying that, does anyone know what Fuel Return to Tank (FRTT) philosophy is for B777 / T800, this may well be an insufficient Flow Number (FN) for these extremely long sector cruises and not prevent the tank fuel volumes dropping below say, -8 Deg C.
I suspect that if system testing is done with fuel in the sticky ice temperature window then lots of engine fuel systems will, shall we say, "fall down" which is a huge can of worms. It's perhaps somewhat fortunate that it was a T800 where a fix is easily "sold". If it had been a GE90 where I believe the FCOC loop is in the HP fuel circuit, therefore intrinsically hotter, then the proverbial would be hitting the fan. As an aside the problem with HP side FCOC loops is matrix tube failure, as significant oil dilution would occur leading to lubrication / bearing "issues".
Again, fundamentally the engine is being asked to deal with an aircraft fuel system phenomena, not exactly chicken and egg.