Yes, an idler pulley spins continuously at very high speeds whenever the engine is running. Because it is bolted onto a sealed, high-speed internal ball bearing, the outer metal or plastic wheel of the idler pulley rotates freely alongside the moving serpentine belt to reduce friction and guide the belt smoothly. If the internal bearing fails, seizes up, or runs dry of lubrication, the idler pulley will stop spinning, create a loud squealing or grinding noise, and can cause the drive belt to snap. You can verify pulley movement by inspecting a running engine bay.
1 votes
Marked as accepted