Too hot for comfort! - Auxiliary fans not cutting in soon en

[DougE280]

Can any of you technical experts help me with a problem of overheating (E280/M104/24V with A/C), only apparent during the recent hot weather?

I?ve read somewhere that the auxiliary cooling fans work independently. One starting at 100 degrees and the other (i.e. both) at 115 degrees.

Whilst idling in traffic in very hot conditions, A/C on, the engine temp goes really hot ? right up to nearly red then (finally) both auxiliary fans cut in together and the temp soon drops to normal?.only to repeat this every five minutes or so.  It?s all getting a bit too hot for my liking and I don?t remember it doing this last year.  I think maybe the 100 degree switch / relay (or whatever) isn?t working.

On the front of the engine, next to the thermostat housing there are two sensors. The front one with one wire I know works the temperature gauge.  The other one has a square plug with four wires.  When I unplug this, both fans come on after a slight delay.

Does this sensor monitor both 100 and 115 temperatures? If so, am I right to assume it need replacing, or is a relay at fault?

Is there any way I can test the sensor before buying a new one?  I don?t want to burn anything out shorting out the wires!

Anyone help?

Thanks

 

[Matt Crooke]

Too hot for comfort!

Apologies if im stating the obvious here, but have you checked the normal cooling fan is working ok, as i thought the aux fans were mainly for the aircon.

 

[DougE280]

Too hot for comfort!

Thanks, but how do I test the engine driven fan?

 

[DougE280]

Too hot for comfort!

Thanks to help from another forum, I checked the two relays in the black box behind the fuses.

The green relay has a 30A fuse which was okay - this is for the high temp/high speed mode.

The blue relay behind it is for the low speed, A/C cooling mode and this relay had a blown 15A fuse.

I replaced this fuse and ....bingo...it all started working properly.

This new 15A fuse blew within an hour and I have replaced it with a 30A and it all now seems okay.

My rudimentary knowledge of electrics makes me think that these two fans must draw the same amount of current whatever their mode/speed of operation - as maximum load/surge occurs at their start-up.

It would have been useful if MB or whoever printed, amongst all the other writing on the top of the relays, the fuse rating.

Anyway, fingers crossed, hopefully this problem is sorted.

 

[Matt Crooke]

Too hot for comfort!

Hi Doug

Sorry for the delay in replying, i have been away for a couple of days. Glad youve got it sorted, did you manage to test the engine fan at all? Also im not sure on your model if you have a Viscous fan or an electromagnetic one. If its viscous the clutches can go eventually, causing the fan to not lock on when the engine reaches the 100 degrees mark. You can test the fan (viscous style) buy letting the engine reach the 100 degrees mark or just above, at this stage the fan should have locked on...give the engine a nice healthy rev, and you should be able to hear a mass rushing of air. If this dosent work, again let the engine reach the right temp, shut the engine off, open the bonnet and see if you can spin the fan with your hand. If the fan is still freewheeling then the clutch has gone, hence the hot running in traffic. Let me know how you get on.

All the best

 

[DougE280]

Too hot for comfort!

Hi Matt,

Problem was electrical after all.  Believe it or not, the two relays were the wrong way round!!!

Stupidly - these relays fit in each others sockets.

The fans now run slowly, intermittently, from about 90 degrees and I'm hoping not to have to experience the "fast" fans at 100 degrees plus! However, I know they work as when I remove the plug from the sensor on the thermostat housing, they speed up after about one seconds delay.

Anyway, it's all sorted now, with the correct fuses.

I tested my main engine driven fan as you suggested - yes, there's no doubt as when it's working and you rev up, it sounds like Concorde taking off!!

Thanks for taking the time to help with this problem.   Cheers,   Doug

 

[Matt Crooke]

Too hot for comfort!

Doug.

Excellent news...funny why the relays were in the wrong sockets isnt it, still at least its foxed at no expense..always the nicest sort of repair!

Glad to have helped.

cheers

 

[oldman]

Too hot for comfort!

My 1988 200T fan does not cut in when it reaches 100C.
The fan seems to spin freely. Could it be the clutch in the viscous fan? How would I know what one I have?
What do I do to fix it?

Cheers
Oldman

 

[dave elcome]

Too hot for comfort!

Oldman.

The best way to determine which fan coupling you have,  is to read the description in the Haynes manual. Without wishing to sound condecending, it's a good "laymans term" description.

Once you've decided which one you have from that, then you can test them accordingly.

 

[Andy]

Too hot for comfort!

Hi Oldman


Firstly the fan should on a 200t spin freely. If you look at the top of the cylinder head you will see a twin pole switch which has a red insert. This is the fan switch. If you bridge the two connections together with a paper clip or long nose pliers. With the ignition on, you should hear the fan click and the fan lock. If it does then the switch requires replacment. If not then there is a problem with the fan magnet or wiring.

Hope this helps.

Regards

Andy @ www.mercedesservicing.com