About what the life of a radiator cooling fan?

When we choose a cooling fan, the first thing to consider is life, can use how long, so the life of the cooling fan with what factors? The Lord is with bearing, then is the environment temperature, the balance of the blades. Ac fan 1. Bearing: double ball bearing life span of the nominal 50000 hours, the service life of oil bearing nominal (3 hours At room temperature under normal) 2. The environment temperature, the higher the temperature, the shorter the life, especially the oil bearing type cooling fan, particularly sensitive to high temperature. 3. Blades balance: blades balance is poor, shaking, noise in the long run is first introduced, then might turn card death