If your vehicle is showing loud roaring noise from the engine fan when accelerating, here are the most likely causes and the parts you'll need to fix each one.
On vehicles with mechanical cooling fans, the fan clutch is designed to slip when the engine is cool. If the internal fluid leaks or the clutch seizes, the fan locks up and spins at full engine speed, creating a loud 'jet engine' roar when accelerating.
On vehicles with electric cooling fans, a stuck relay or failed control module can cause the fan to run at 100% maximum speed constantly, regardless of engine temperature.
If the coolant temperature sensor fails or sends an erratic signal, the engine computer will often command the cooling fans to run at maximum speed as a failsafe to prevent potential overheating.
If the fan clutch was recently replaced, installing a 'severe duty' or 'heavy duty' fan clutch instead of the standard OEM specification will cause the fan to engage much more frequently and loudly.
The engine computer monitors A/C system pressure to control fan speed. A faulty pressure switch can falsely report extreme high pressure, causing the computer to command the fans to roar at full blast to cool the condenser.