Why the clutch fans have a bad rap?

[sapote]

I had read that some owners have bad experience with the clutch fan – it locked and spin too fast leading to high noise then broken fan blades and causing damages to other parts around. One thing I noticed that these fans don’t like to be stored laying flat. Worst, when laying flat with the nut points up it starts to leak oil from the front face. Laying flat with the nut down for long term is OK, but watch out before install it back on the engine as it could lock up and spin too fast. Before install the fan make sure you turn the nut relative to the fan (for the internal oil to move out of the locking position during the times when it was laying around) until it feels loose. When working on the car, don’t lay the fan flat but keep it up right as when it mounted on the pump shaft, as this prevents the clutch locking up.

[Fresh1179]

To answer the question in your title, at the risk of starting an unnecessary debate, I think the fear or "bad rap" the E46 clutch fans get is a bleed over from catastrophic failures in the E36 where the blades fail leading to a shrapnel type detonation. I don't believe this issue is nearly as prevalent with our cars as it was with the E46, and I know some guys that have run their E46 as a dedicated car with a clutch fan for years with no issues. I guess it comes down to maintenance. If the clutch fan develops cracks, your gonna have a bad day.

[sapote]

No, I’m talking a normal healthy fan could lock up if it was laid down before being installed.

[mrgizmo04]

The clutch mechanism works somewhat similar to a thermostat. That slightly bent plate across the front of the clutch with brand/writing on it actually deforms based on temp, opening galleys inside the clutch to release the fluid from a central reservoir to the edges/fins of the clutch.

The clutch fails in 2 opposite ways.
1. When the car is overheating because there is no fluid in the clutch (it all leaked out) and therefore the fan it free spinning separately from the waterpump/engine without locking/engaging so the fan blades don't actually cool. 2. Is when the clutch fails in the open position so that it's always locked/engaged so that the clutch and fan blades spin with the waterpump/engine to whatever rpm (usually high on track). The assembly is not perfectly balanced, plus you can have some play in waterpump bearing, which at high rpm makes the clutch/fan blades disintegrate.

I've seen both cases - clutch/fan blades disintegrate on track, I also know people with north of 150k miles who track hard with mechanical fan in place without issues. I think replacing fan clutch and waterpump (due to potential bearing play) at decent intervals helps alleviate the problem.

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