My viscous fan roar, especially with the top down, is certainly annoying. I have searched many of the posts, so I believe that the fan at least works, but is it working properly? At a steady 1500 RPM the fan constantly engages and disengages. I get the roar and then peace and quite. This repeats approximately every 20 seconds. What would cause this?

Thanks

BD

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87 560 SL
93 300E 2.8
91 300CE-24