Rockhound,
Most jet aircraft have a higher fuel flows to the engine than what the engines needs.
It uses the excess fuel flow to cool the engine, the heat is absorbed by the fuel warming the fuel which cools the engine and then recirculated back to the fuel tank.
Excess fuel is continuously circulated in this manor which prevents the fuel from getting too cold, and the engine too hot.
This is a very simplistic explanation of the process.
