Hello,I noticed something strange while i fly with PMDG b737-800 NGX,First, I read in the manual that fuel temperature should not go less than 3 degrees CelciusI was on FL360 south of France, the TAT was -36, the fuel temperature became about zero degrees Celsius or less, i was cruising on the most possible speed.When i landed, the outside temperature was 16 Celcius, but still the fuel temperature is zero or less!!I think there's some sort of fault in the fuel temperature gauge and system.Thank you for help.

Fuel tempreature takes awhile to go in either direction. It is not an instant thing. Just because it is 16c outside does not mean that is what temperature your Fuel is going to be.In other planes in the past people are used to seeing the fuel temperature being exactly what temp the outside temp was and not realistic. The NGX accurately simulates how fuel temps would be in the real world.Another example would be if your flying from the tropics to Alaska. Temps will start high and very slowly move downward as you go into colder coniditions. Then if you take off from Alaska and fly down to the Tropics your going to have cold fuel at the start.There was a thread on this a couple weeks ago. Search for Fuel Temperature and you should find it.

Why does the manual say that it should not go under -3°C? I thought that cerosine remains fluid down to approx. -40°C?!

You are right! Thank you very much for your clear answer.

LHPilot: it will cause all kind of problems with icing as you descend and frost begins to form on wings (that are cooled bu the fuel). There is the black outline on NG wings, that marks the place where frost is allowed, but if it is over the line, you need to deice. That can be problematic in summer or in warmer destinations.accordingly if you let your fuel get too cold, you will have a problem later on in flight, or, hopefully only, get delayed on ground.Some airplanes, like MD-80 family, offer wing heating blankets to alleviate this issue. You can read a bit about it for ex. here: http://www.tdgaerospace.com/iceprevention.php

Limitations: Max fuel temp +49ºC, Min fuel temp -45ºC

Typical freezing point of Jet A1 is -47ºC. If the fuel temp is approaching the lower limits you could descend into warmer air or accelerate to increase the kinetic heating.

Not sure whats up with the 3c thing that doesn't make any sense to me either.