Have you already ruled out the fan clutch as it is the device that engages the radiator
cooling fan as the engine becomes hotter. I think the electric fans are related to the air
conditioning. The fan clutch is a commonly replaced item. You should be able to
hear a change in the amount of air blowing when it is engaged. It should be engaged when
the engine is cold and will release after running for a short time like 30 seconds or so and
it should also then engage when the engine is hot. This is not to say you may not have other issues , but the fan clutch is definately related to cooling when the temperature
rises.