In our 744 FCOM there's one sentence in the engine fuel section that says engine oil heats the fuel in the heat exchanger. In the engine oil section there's one sentence that says the oil is cooled by the fuel in the heat exchanger. And that's how all that stuff works.
On the Seven Two there was a max fuel temp around 55c. At that point the fuel would not be a heat sink and you could cook the engine. Probably why Pratt suggested the engine change.
I've seen the other end. Minus 20/25 fuel. Everything nice and warmed up and when T/O thrust was set the oil temp dropped off the bottom of the scale. Pressures were still good at V1 so we keep going. Oil temp gradually came back into the green as we climbed.