W124 (1989) Engine Cooling Fan - Electromagnetic Fan.

[NormanB]

W124 (1989) Engine Cooling Fan - Electromagnetic Fan Clutch.

Hi

I had a bank holiday motoring experience today and I feel a 'reet chump'!

Basically spent an hour in start stop conditions and engine temp rose...and rose until (I suspect) the expansion chamber pressure cap lifted and let go of the coolant - it was quite impressive. Fortunately I managed to slide over into a vacant parking slot within 10 metres!

Opened the bonnet and satisfied that it was not on fire (had a 'FUD' moment (fear uncertaininty and doubt)) and that there was only oil in the sump, fed the meter and took my daughter to the planned trip to the cinema to see Harry Potter, which fortunately was only a ten minute walk.

On return, the engine was nice and cool, rechecked the sump and relieved to find only oil and at a normal level. Topped system up with oggin and ran engine which soon reached normal operating temperature and thermostat opened at spec. No leaks found.

My guess is that the electromagnetic fan failed to cut in. What are my options where is the sensor - how can I test the unit electrically and is there a strip out option on the fan clutch or is it upkeep by exchange.

Grateful for any techie advice, wise words or guidance.

NormanB

PS: I fell asleep within the first 10 minutes of Harry Potter, my ten year old daughter is well trained and left me alone until I started snoring!!
She tells me it was a really good film!!

 

[silverarrow]

go for a fan switch or relay or both sometimes not sure on your model if switch is near thermostat to check fan works run 12 volts through the 2 wires and she should spin and do check fuse.

 

[NormanB]

Fixed

Thanks for that.

Just to let you know and for those that follow.

The thermo-switch had failed. This is the brass coloured 'jobby' at the front of the head beside the thermostat. A 22mm deep socket is required to remove and replace. The electrical connector is rectangular in shape and there are 2 pins on top of the thermo-switch. The original had an aluminium sealing washer, the replacement came with a copper one.

The dealer had them in stock but there are different part numbers so you need to provide chassis number - cost £16.

You can test if the electro magnetic clutch is functional by bridging the two connections of the rectangular plug with the ignition on - you should hear a 'clunk' and you will be unable to turn the fan by hand - unlike the condition without the bridge or ignition off when it should freewheel.

Time to replace - max 10 minutes including supping a mug of tea! :bannana:

To be honest I reckon this had been duff for yonks I just had not experienced such a lengthy period of stop/start traffic before.

For those with a electro magnetic clutch on their engine fan I most heartily recommend that you carry out the test described above - particularly as summer is supposed to be happening some time soon.

 

[guydewdney]

same doofer went belly up on my 140 - same price (ish)

twhe twin fans - with twin speeds - didnt seem 'right' - so replaced. now better in bad traffic.

 

[Ian B Walker]

Hey Norman thats a great tip. Thanks will give it whirl in the morning. :bannana: :bannana: :bannana:

 

[NormanB]

Hey Norman thats a great tip. Thanks will give it whirl in the morning. :bannana: :bannana: :bannana:

Part 2 of the test is to test the function of the thermo switch itself. The non scientific way, which is the way I did it ;-) is: On return from a trip out with engine at normal temp, leave in neutral and let engine idle at around 1500 rpm, have the bonnet popped open (and radio off), observe temp rising....

When the switch closes and energises the clutch you will hear the same noise you heard in Part 1 of the test and the fan will spin at engine rpm. You can test it by introducing a carrot to the tip of the blades - if it is being driven then the fan will not slow and the carrot will get sprayed around the cowl - messy - but not as messy as using a finger.

As far as I could guessestimate from the instrumental panel the switch closes at around the 105 C mark.

I think mine had deffo been duff for a while because I had seen temps higher than that - briefly.

The more scientific way would be by testing the switch in an oil bath (deep fat fryer) with an independant thermometer and a multi meter rigged. SWMBO hates me using the kitchen for things like that.