Originally Posted by sooty655
If you swap the flow paths between fuel and oil, the result will be warmer fuel and much less well-cooled oil.
Sorry, that is thermodynamical nonsense.
If the fuel would be getting warmer, it would mean that more heat (energy) was transferred to the fuel. All energy that is transferred to the fuel, must come from the oil (disregarding other heat sources for the sake of the argument), which means that the oil would also be cooled more.
What you state above might be true if the flow
rates would also be exchanged along with the flow paths. But that is not possible, since both the oil and the fuel flow rates are dictated by operational conditions.
Bernd