Why those old Renaults have the radiator behind the engine.

Because the flywheel can then be the fan. Of course nobody was going to notice this answer on the FP.

Here’s a view from the back, under a Renault truck:

Weirdly, flywheel fans were sort of common for a period of time around 1910. Although most cars kept the radiator up front, and the engine was “sealed” with an under-tray and an air-tight hood to keep air flowing through the engine compartment, and out the back, through the fan.

Weird huh? Renault did the smart thing and put the radiator near the fan (instead of what everybody else eventually did, which was put the fan near the radiator).