which series are you talking about? 1,2,3 or 4

In the 400 series the fuel is heated by the FOHE or Fuel Oil Heat Exchanger. The oil is pumped from the engine to the fuel collector bay on the inboard portion of the wings where two things happen 1. The hot oil heats the cold fuel and 2. The cold fuel cools the hot oil. It is a win win situation for both systems.