The cooling fan on my 2002 E430 has been running a lot more often than I seem to recall from previous summers.

Can anyone describe the engine fan cooling system logic (i.e. what triggers it to come on, which sensors are involved, etc.) on this 210.083 vehicle?

The symptoms that I have are:
(A) Cooling fan not engaged when starting the car (cold)
(B) Cooling fan engages when the H20 temp reaches ~85C (based on the dash gauge) with the A/C running
(C) Once the cooling fan is engaged, is never seems to disengage (until the engine is shut off) - even at highway speeds 55+ I can still hear the main fan running (the H20 temp gauge on the dash is solid at just over the 80C line)

This seems to have arisen after I replaced the voltage regulator on my alternator in April - so potentially I damaged some of the wiring or inadvertently disconnected some sensor.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE

You sure they are running at highway speeds? Normally they shut off there. Could be the temp input sensor on the front of the motor is failing and saying it is hotter than it is. Which is probably why it doesn't shut off still thinks its too hot.

ON that car the aux fan operation IS heat (engine) & pressure (a/c) dependant.

When the a/c pressure builds to 225+- psi the fan will start to run.
And when the engine reaches 210+ the fan should run even with the a/c off.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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MB Doc - are you referring to the dual aux fans in front of the radiator/condenser?

The fan that is staying on in my case is the main engine fan (i.e. the one between the engine block and the radiator)

If we're talking about the same fan let me know.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE

I'm still having trouble with the single/main engine cooling fan - it seems to be engaged constantly.

What causes this fan to come on?

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE

Is that an electrical fan or a viscous fan clutch system?

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Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter

Skiier 3 9,

You're describing your Viscous Fan Clutch driven Mechanical Fan.
(In Between the Engine and the Radiator)
The Bi-metallic Actuating strip facing the Radiator on the front of the Viscous
Fan Clutch Actuates based on the flow of HOT air supplied by the Radiator.
[AD and GSXR are continually reminding us that a COLD spot on the Radiator
in front of the Viscous Fan Clutch will prevent it from Actuating.]

The Viscous Clutch is supposed to Dis-Engage at higher engine RPMs.
(I don't know disengagement specs for the Gassers)
But Reving the engine to higher RPMs should disengage it...If not you'll hear
the Fan "Roar".

I have speculations about your Viscous Fan Clutch
(AND your Dash Temperature Gauge reading)
BUT,
This is positively a M.B. Doc question [Expert]

Attached Thumbnails

 

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'84 300SD sold
124.128

I believe you may have just led me to the cause.

When I was trying to remove my alternator to address the charging issue earlier this year I bent that little strip of metal on the front of the fan. At the time, I briefly considered removing the fan/clutch assembly to give me more room to try to work on the alternator. I bent the strip thinking it covered a screw on the front of the fan...

I doubt I'll be able to bend it exactly into the right position...

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE