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Registered 2010 SLK350
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47 Posts
Discussion Starter #1
Just wondered if anyone could help, when I start up our 2010 SLK350 from cold, the cooling fan starts up approx 10 seconds after car has been running, and sounds like like a 747 on take off!


Surely this isn't right?


I have owed the care since October 2018 and I am sure it didn't used to do this when we first acquired it.


Any ideas??
 

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Registered 2010 SLK350
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47 Posts
Discussion Starter #4
"Could it be the secondary air pump? That would be normal. Just a thought"


Nah, its definately the main radiator cooling fan that is running, it sounds like you are stood next to a 747 at take off and blows like a hurricane under the bonnet.
 

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Administrator 2009 SLK 55 AMG/Founding member 2006
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94,921 Posts
besides doing what i860 suggested, no harm in resetting the battery

disconnect neg cable for a minimum of 30 minutes
reconnect cable
reset clock, synch windows


does it still make noise?

how old is battery? :D
 

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Registered 2010 SLK350
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47 Posts
Discussion Starter #6
The battery was new last October, about two weeks after I had purchased the car. I checked the battery afetr it seemed weak, and it was the original battery that came with the car 10 years ago.

So new one fitted.
 

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Registered 2008 SLK350
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2,266 Posts
What i860 says.
Have it scanned for errors.
The fan has an integrated control unit that receives a PWM signal from the ECU. Duty cycle of the PWM specifies the speed at which the fan runs.
10% duty cycle is fan off,20% is minimum and 90% is max.
If anything goes wrong with this actuation process the fan automatically goes into emergency mode and runs at full speed.
Which is what happens in your case I guess. Could be a bad control unit.
 

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Registered 2007 SLK350
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560 Posts
I do not know the answer to this, but would the "emergency mode" not also be triggered by a faulty sensor, such as cooling temp?


My limited experience is that this is what some other cars do. Disconnecting the water temp sensor is often the normal way to test the cooling fan is working!!!



Of course needs diagnostics scanner to identify, but maybe the dash cooling temp indicator might give a clue.
 

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Registered 2008 SLK350
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2,266 Posts
I do not know the answer to this, but would the "emergency mode" not also be triggered by a faulty sensor, such as cooling temp?


My limited experience is that this is what some other cars do. Disconnecting the water temp sensor is often the normal way to test the cooling fan is working!!!



Of course needs diagnostics scanner to identify, but maybe the dash cooling temp indicator might give a clue.

Yes,you're right. Also a possibility.
 

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Registered 2004 SLK350
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178 Posts
It's not that warm in the UK and it's a variable scroll compressor...or how they call it....it should't start the fan, I guess.

As said before: secondary airpump can make a whining noise after start up...
 

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Long Time Member 2005 SLK350
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3,698 Posts
It's not that warm in the UK and it's a variable scroll compressor...or how they call it....it should't start the fan, I guess.

As said before: secondary airpump can make a whining noise after start up...
i hardly have my A/c on and once in a blue moon i have hit the AC button by mistake when i have started the the car and put heating on. by time its out garage and i have locked doors ect and got ready to drive of the fan is running at a higher speed than normal. only reason i asked as i have noticed it in the past........p.s its always hot and sunny in the uk :grin::grin::grin::grin:
 

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Registered 2010 SLK350
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47 Posts
Discussion Starter #13
No, not got the A/C on.


And just for your info, its been a barmy 7.5 to 12.5 degrees C over the last weekend........but still no need for the A/C


Booked in with local MB Independent garage on Thursday to get checked out/diagnostics, hopefully cheap outcome!
 

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Long Time Member 2005 SLK350
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3,698 Posts
No, not got the A/C on.


And just for your info, its been a barmy 7.5 to 12.5 degrees C over the last weekend........but still no need for the A/C


Booked in with local MB Independent garage on Thursday to get checked out/diagnostics, hopefully cheap outcome!
look north said 16 this satdi !! ...never happen

hope you get it sorted

cheers pete
 

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Registered 2010 SLK350
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47 Posts
Discussion Starter #15
Cheers Pete,


Hope it is 16C this Saturday, could be a good weekend, kids staying away so no cars blocking me on the drive, just me and the wife, top down (the car, not the wife) out cruising then......


I won't hold my breath though
 

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Registered 2010 SLK350
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47 Posts
Discussion Starter #16
Problem sorted.


It was the main cooling fan that was running 100% in emergency mode, as the A/C refridgerant gas sensor was not reading any gas in the system!


Sensor replaced and all good, no fan noise just the burble of the V6........
 

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Long Time Member 2005 SLK350
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3,698 Posts
Problem sorted.


It was the main cooling fan that was running 100% in emergency mode, as the A/C refridgerant gas sensor was not reading any gas in the system!


Sensor replaced and all good, no fan noise just the burble of the V6........
I was on the rite path..( A/C)........close buy no cigar :smile:

Glad sorted
 

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Registered
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11 Posts
Just wondered if anyone could help, when I start up our 2010 SLK350 from cold, the cooling fan starts up approx 10 seconds after car has been running, and sounds like like a 747 on take off!


Surely this isn't right?


I have owed the care since October 2018 and I am sure it didn't used to do this when we first acquired it.


Any ideas??
Had the same issue with mine. Fan would run uncontrolled when key turned on. Took the gamble and replaced the Temp Sender unit located at the back of the block and all is well again. Also noticed a another alarm regarding coolant level which was clearly ok when i looked . Apparently the two sensors are on the same circuit. My fault finding knowledge tells me to replace one thing at a time which in this case paid off. $30 and 15min to swap out.
 
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