W124 - Cooling fan

[mekon]

Hey guys, having a problem with overheating when the car is idle, radiator etc is all fine, so aslong as we keep moving its ok, but the fan is not being driven by anything just spins freely, can anybody tell me how it is driven?

Engine is the simple 2 litre petrol, not fuel injected or anything complicated or high tech

Thanks in advance guys

 

[grober]

Age of car required. If its the old single cam engine also shared with the 190 the fan has an electromagnetic clutch. It is switched on via a thermal switch on the cylinder head. These can go faulty and the fan won't switch on-test by shorting it. Cure is to replace the switch. If its the later twin cam engine found in the C class its a viscous coupled fan. If its not working I.E. doesn't fully engage when engine temperature rises ( take it off--warning counterclockwise thread -and check the bimetal strip on the front is clear of debris/road muck -clean gently with wd40 and a tooth brush-keeping the unit vertical at all times) you will have to replace it.

 

[television]

You can see what fan you have by looking at the fan housing,, the electric clutch versions have two thin wires coming out of the top and one goes to the sensor nearest the front of the engine, on top

 

[mekon]

its an 88 car, i shall go find my pliers and pop the bonnet... silly merc using a plastic release thing GRRR

how much am i looking at for a new switch if it is that? cant see them listed on GSF

 

[television]

It would be better if you posted the next 3 VIN numbers after 124???

 

[mekon]

confirmed two wires coming out, one to a sensor thing im guessing.... wat do i short to where to test the clutch?

 

[television]

The wire that comes from the fan and goes to the sensor, just start up the car and ground the sensor top wire and see if the fan starts, I think there are 3 sensors in all,and it is the one nearest the front

 

[mekon]

two wires, one is connected straight to ground, the other goes into a box (guessing sensor) tried grounding it with engine running, fan still spins freely, could i hae grounded the wrong wire? not alot of space in there, did i ground it too early in the circuit perhaps? i would send a picture but my cam has gone missing

 

[television]

I know that the 190 works by grounding the sensor.

OK this means that if one fan wire is grounded then the other needs a 12 volt plus, and this must be in that junction box. Can you open the box

 

[mekon]

junction box? where is the box? the other leads to small box with kinda one prong in it, that then leads out down to a circular box with many numbered.... holes...kinda thing in it (i got nosey and opened it a minute ago)

that the junction box?

 

[mekon]

found thermal sensors on GSF, looks like the one i should be grounding would be two pin however the one i grounded is a one pin.... perhaps i grounded the wrong thing? theres a red two pin object connected front of the engine, could this be sensor? the wiring in this engine is quite convoluted, and alot of it goes into black sleeves which twirl around each other and go through places making it hard to follow

 

[television]

junction box? where is the box? the other leads to small box with kinda one prong in it, that then leads out down to a circular box with many numbered.... holes...kinda thing in it (i got nosey and opened it a minute ago)

that the junction box?

Sorry connector block / junction that was what I meant, tell me a do any of the sensors on top have 2 wires on them as the sensor could be fed with 12 volts and switches and closes when warm, in this case joining the 2 wires together would start the fan.

You could use a meter on the Ω stting to see if the clutch is O/C

 

[mekon]

its not o/c just checked, the red one has two wires/pins all the rest are single. ill try shorting the two pin red one with the engine going, see if that starts the fan

 

[mekon]

just ran a voltage check on that twin wire/twin pin sensor thing, there is a tiny charge of 0.6 going accross it... not twelve

 

[grober]

Just short across the 2 pin sensor. You will hear a distinct change in the sound of the fan. Have the engine running when you do this and watch your fingers.

 

[television]

As Grober just sort them the 12 volt is in relation to ground

 

[mekon]

tried shorting the two pin sensor both the pin side and the socket side, neither engaged the fan,

ran a volts check across the single wire thats not grounded appears to have nothing going accross it

 

[television]

tried shorting the two pin sensor both the pin side and the socket side, neither engaged the fan,

ran a volts check across the single wire thats not grounded appears to have nothing going accross it

Then take a 12 volt feed and connect to the fan + wire that will eliminate the clutch

 

[mekon]

im getting tempted to just solder the bloody thing to the spinning object immediately behind the blades, then it would spin!, take longer to get the engine to running temp but i do occasionally go into places with other cars and even occasionally theres traffic (im in very rural norfolk hence didnt notice the overheating unless at idle, never got stuck in traffic!)

 

[mekon]

12volt feed direct from the battery be ok?