Cooling fan not working?

BillyBoy

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Hi,

Had a drive down to where I used to live in Wycombe today, and car was fine, but driving round town, and especially up the long step hill (very slowly in traffic behind a lorry) the temperature needle was right up on the red. Got to the top of the hill and the display came up red warning me of overheat and to stop engine.

Stopped and turned the engine off. Checked under the bonnet, and there were slight traces of coolant round the top of the header bottle, but couldn't see the level. Left it for a few hours, and then checked coolant level. This was fine. Started and drove back in to town to pick my brother up, and the temperature was rising whenever I was stationary for a period of moving slowly. Once I got clear of traffic, and all the way up the motorway, it has been fine.

I'm therefore strongly suspecting that the fan is not cutting in. I plan to have a look at it tomorrow as it's a bit late now, but not sure how it works. Is the fan controlled by a simple temperature switch, or is it directly off the engine management system? I'm pretty sure I'll be able to find a plug somewhere so I can stick 12 volts straight across the fan to see if it's the fan itself, or lack of power to it, but if it's the latter, I'm not sure how the power is routed.

Car is an S320 CDi W220 facelift.

Many thanks in advance,
Bill
 
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BillyBoy

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No, it's definately electrically operated. I checked all the belts and pullys as that was my first thought too, but they are all intact.

Thanks,
Bill
 

television

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See what I can find in the morning
 
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BillyBoy

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Thanks Malcolm, much appreciated if you can.
 

television

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Fuse number 33 rated at 60 amp is for the fan.

Fuse 48 and 49 are 15 amp fuses for the fan control module N65/2

You have a fan relay module K40/7kp in the fuse box.

There is another fuse F28 for this module
 
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BillyBoy

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Thanks Malcolm, but not sure this is correct - according to the fuse designation diagram for my car, the engine fan is f30, f44 and f87. It lists the ones you've stated as:

f33 - Blower motor AC

f48 - not used
f49 - ignition coild (presumably not on mine as it's diesel!)
f28 - Fanfare horns

Cheers,
Bill
 
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television

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Well I did it the 220126 there are 4 versions
 
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BillyBoy

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Sorry, that's me not providing enough information. The first part of the VIN is WDB2200252A, so I'm guessing that's different to a 220126?. Don't understand why Mercedes have to make it so complicted!!

Many thanks for you help.

Cheers,
Bill
 

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Yes yours is the 04 version on.

Were the fuses all good
 
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BillyBoy

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Unfortunately yes. I also couldn't find any connector that was readily accessible to try a direct 12 volts to the fan, and there's not a lot of space round there to get at anything. The wired seem to come across a mounting between the rad and the blades into the fan housing, but I can't see where they go from there. There's a big electrical gizmo at the bottom of the housing, but it looks far to big to be a fan controller and has some heave duty cables running to it (I'd say about 8 - 10 mm2) plus a couple of thin ones which I presume are the data cables.

The fan is free moving by hand and feels like it is still on the motor shaft rather than slipping on it. Fortunately, the time I go in to work, there's not a lot of traffic about so I should be OK tomorrow. There's apparently a pretty good indie just down the road from out office who has a couple of ex merc technicians working for him, so I may just have to pass it over to them. I'm kind of loathed to do much under the bonnet these days, especially without wiring diagrams or a manual - how I miss my old Cortina where you knew exactly what every part under the bonnet did!!!

Thanks for your help on this and all the other occasions.

Cheers,
Bill
 

television

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Bill if you get stuck in traffic, just put the heater on full and hot, that will keep the temp down, this could be just the sensor switch that operates it all, not easy without instruments
 
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BillyBoy

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OK, Car's going in tomorrow to (hopefully) be sorted. Quick question - does anyone know what temperature the engine fan should cut in at? My car normally runs at around 70 degrees acording to the temperature guage, as did my E-class with essentially thesame engine, so I presume this is normal. I've left it idling and it climbs up to just over 80 degrees without the fan cutting in, then I got bored of aiting and turned the engine off. I'm thinking that the fan should have cut in by then as that's a lot hotter than I have seen it under "normal" conditions.

Cheers,
Bill
 

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You have an engine fan on the engine that cuts in at 90c roughly and an electric one that cuts in at 100c in the rad, though this one mainly comes on when the air con is in use
 

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Bill if you get stuck in traffic, just put the heater on full and hot, that will keep the temp down, this could be just the sensor switch that operates it all, not easy without instruments


would it be worth checking if the fans are working with the air con on, & if so use of aircon would be a useful stratagy for some radiator air while stuck in traffic, while awaiting the full repair?
 
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BillyBoy

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Sadly my diagnosis was confirmed by the garage - the cooling fan is shot. The bad news is that it only apparently comes as a complete assembly with the Fan, control unit and cowling at a cost of some £530 + VAT!!

Going to see if I can source something cheaper, but also, can anyone help me find the correct diagrams on http://www.detali.ru? If nothing else it will ehlp me track the correct part number, and there may be some breakdown into smaller parts. I can get as far as a page listing lits of W220 models and it has a link for S 320 CDI (220.025, 220.125) which is my car, but the next page is 100% russian and I can't read or speak a word of russian.

Any pointers much appreciated.
Cheers,
Bill
 
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BillyBoy

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That was for a genuine MB unit. The garage tried phoning round but couldn't find anything other that a genuine one (hence my attempts to get one myself at a more reasonable price :)

Was that £250 from MB to supply or a third party?

Cheers,
Bill
 

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