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Old 01-08-2003, 09:37 AM
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Does the fan speed increase with engine speed?

My fan bearing is on its way out at 186,000 miles and I plan to take care of it soon after reading threads on this subject. My question is does the fan speed increase proportionally to the engine speed or is there a limit to the speed? This car is my daily driver for me and my two kids and I don't want a major breakdown or get stuck some where with the kids in the car.
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Old 01-08-2003, 10:05 AM
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Join Date: Apr 2001
Location: Dallas/Fort-Worth
Posts: 5,711
Actually you have three fans...the main fan behind the shroud and two auxiliary fans.

The main fan is on a clutch, and when engaged, it does spin in proportion to the engine speed.

The auxiliary fans get a signal from the temperature sensor to indicate that additional cooling is needed, and they spin a either a fixed low or high speed, depending on cooling demands.

Actually the W124 cooling system process is a bit complex, with all sorts of backup plans to handle overheating issues. One such plan is that the A/C compressor gets shut down under dire circumstances.

If the weather is mild (not hot) right now, you should be okay.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car
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Old 01-09-2003, 02:56 PM
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Join Date: Apr 2002
Location: Surrey, Uk
Posts: 254
I thought the main fan was on a viscous coupling. When engaged it runs roughly in proportion to engine speed up to a maximum of about 3000rpm when it doesn't go any faster.
Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)
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Old 01-09-2003, 04:08 PM
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Join Date: Dec 2002
Location: Visalia, CA
Posts: 379
If you're talking about the engine driven main fan and the respective bearing..... the viscous coupling will/can/should keep the fan itself from spinning too fast, BUT the pulley and bearing hub are still driven by the belt and will continue to turn at engine speed. With a mechanics stethascope (or long solid rod ie; extension ) you should be able to listen to all bearings and track down the noise, just beware of moving parts!!! Hope this helps and good luck!!
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