The clutch fans have a built in thermostat (usually a bi-metallic spring, either internally or externally) that begins "locking" the fan up at a set temperature. When the bi-metallic rotates with increased temperature, it moves a valve within the fan and redirects the viscous fluid within to start locking the fan up, bringing it closer to engine water pump RPM. A locked up clutch would be the cause of your increased air flow noise level. Years ago, in the middle of no where, I had one fail to lock up and caused an overheat. I ended up waiting for it to cool off, removed the fan, beat the crap out of the front of the clutch with a hammer and punch until it was locked up, and then put it back on and drove on until I could get a new one.
Sometimes the valve will stick and keep the fan locked up. I've also seen them where they wouldn't engage at all, either due to a bad spring/valve, dirt and crap on the external spring, or a loss of fluid. It's also possible the clutch is one that has a setting lower than what is desired.
A unit that is working correctly should be free wheeling upon initial cold start, and it should be turning noticeably slower than engine water pump speed. As the engine warms up the fan will begin picking up speed and if the engine temperature gets to the full activation temperature, you be able to hear it loud and clear. Back in the old days, when this type of fan was real popular, we used to have a couple tests to see if the clutch was working at least semi correctly. When the engine is at operating temperature, have someone shut the engine off when you're looking at the fan. The fan should turn no more than about 2-3 revolutions after engine shut off. Another unscientific test we used to do to check degree of lock up was to take a rolled up newspaper and, with the engine fully warmed up and running at idle, stick the newspaper into the fan blades. It should not be able to easily stop the blades from turning. If the blades are easily stopped, the clutch is probably not working as it should.
On yours, I'd for sure check to see if it is the correct fan, and not some "universal" that may not have the proper setting that corresponds with you thermostat temperature. My guess is, as much as I hate to say it, the factory unit is probably what you should get, unless you can find out the correct activation temperature and verify the new one is of the correct setting. If it's still making lots of noise, a few things could be going on...the one that was in there to begin with hasn't been working as it should have for quite some time or the new one is either working correctly, has the wrong setting or a stuck thermostat.
Another option from the old days, if you don't want to pay the big price for the viscous fan clutch, is to put some sort of flex fan on it.....fiberglass or stainless steel. Your noise level will be slightly higher than you're used to, but you'll never have to worry about clutch failure again, and your engine will run closer to your thermostat temperature under most conditions.
Good luck and let us know what you find out.
