AeroTech
-May be these de-oil solenoids are also fitted in APUs that usually operate in cold airports?
You have missed the point. The APU compartment on is non pressurised or heated area...therefore the the APU is subject the atmospheric conditions the aircraft is in.
Most large aircraft will cruise at 30,000 to 42,000 feet altitude.
The airtemp at this height is somewhere around -40 to -56 deg C
You could land in the middle east on a 42 deg C day and still reqire a de-oil device during start due to the fact that the APU has been cold soaked from the previous flight.
doh....
NB i seem to remember the 331 fitted to the A330/A340 has a small heating element that kicks in at sub zero oil temps to prevent the oil from freezing