Some thoughts .......
If these are being used in an automotive environment, are they pushed up against the radiator ?
How much clearance is there between the blades and radiator ? Is there any play in the shafts that allows an aparrently large clearance to reduce when under load ?
Do the fans draw much more current when an air obstruction (i.e. the radiator fins) are close to the fan ?
Are the fans being used the right way round ? If a car is travelling at 60+mph and they are trying to blow against the wind hitting the front of the car, this will massively increase the current draw.
If these are being used in an automotive environment, are they pushed up against the radiator ?
How much clearance is there between the blades and radiator ? Is there any play in the shafts that allows an aparrently large clearance to reduce when under load ?
Do the fans draw much more current when an air obstruction (i.e. the radiator fins) are close to the fan ?
Are the fans being used the right way round ? If a car is travelling at 60+mph and they are trying to blow against the wind hitting the front of the car, this will massively increase the current draw.