Is this a carrot test fail?

[Rob77]

I see there have been a few posts on this lately, well here is my problem:

The car is almost solely used for longish trips, motorway, etc. and the temp is always a couple of hairs above 80 deg. That is, until stopped by roadworks and the like. When stopped, the temp will rise to 110 deg or so then return to just over the 80 deg mark once moving again. This has never worried me as it doesn't occur that often, until last weekend when I was stopped in a traffic queue for nearly half an hour. The temp climbed slowly on up until I felt I had to pull over, switch off and wait until it cooled.

It's been ok again ever since but I did the carrot test today. When pushing it into the blades, I could feel pressure against the carrot and it got a little chewed up at the tip. But I could overcome the pressure of the blades and push the carrot in further until it stopped the fan.

Is this a carrot test fail (it was a fresh firm carrot) and, if so, does that sound like it's the problem? Generally, I buy the (MB) parts and hand the car into my local garage for them to fit so should I be buying a new fan coupling?

I'm thinking I should be getting a new thermostat too and maybe a full flush to be on the safe side. What does anyone think?

Oh and I didn't think to do the same with the 2 aircon fans, at the front. Should I have?

 

[Dieselman]

That sounds like a fail to me, when the engine is hot the fan shouldn't stop.

The electric fans should only come on over about 110 degrees and with the aircon on.

 

[Rob77]

Thanks dieselman. I simulated the sitting in traffic, when hot, problem and could stop the fan with the carrot, although there was some resistance to it stopping.

I think I'll get a new fan on/off coolant senor switch (apparently it sits on the top of the engine), thermostat and a full flush.

I'll also check out the price on an electromagnetic fan coupling. I gather they're pretty expensive though and, if so, I'll get the garage to test mine electrically before I replace it.

 

[television]

The carrot test applies to the Visco fan and not the electric,engine fan, thats the one that uses the top front sensor and also cuts in at 80c, they are not that powerful. The other two come on around 100c.

 

[grober]

you will probably have the electromagnetic clutch fan on a w201. the switch works by earthing a 12v supply which should be present at the coupling connection when the ignition is switched on. It completes the circuit at 100c for standard cooling 2 pin switch and at 110c for cars with aircon 3pin switch and a double pole relay. heres a pic

 

[Karl]

If it's the two pin switch you can test it by disconnecting the wiring plug from the switch and linking the connectors with a piece of wire.
With the engine running you should hear a click and the fan clutch should engage causing the fan to draw air through the radiator.
PS make sure you locate the correct switch as there will be a sensor for the temperature gauge as well.
Don't be tempted to short anything to the engine block!
Good Luck

Karl

 

[Rob77]

you will probably have the electromagnetic clutch fan on a w201. the switch works by earthing a 12v supply which should be present at the coupling connection when the ignition is switched on. It completes the circuit at 100c for standard cooling 2 pin switch and at 110c for cars with aircon 3pin switch and a double pole relay. heres a pic

Thanks grober, do you mean there's an "either/or" 2pin/3pin switch (G & H in the pic), depending on whether it has aircon or not? I have aircon so does that mean it has the 3pin switch and it won't kick the fan in until the temp hits 110deg? And is item 68 the fan coupling?

I thought the fan was meant to kick in at 92deg.

Apologies too if I'm being a bit dense here. Electrics have always been a mystery to me

 

[blue190]

i was having same trouble with my w201, i fitted a new 3 pin switch which was set for 100 deg and a new thermostat and the problem seems to have gone.

 

[LastMinute]

I thought the M103 used a viscous fan coupling?

 

[grober]

Thanks grober, do you mean there's an "either/or" 2pin/3pin switch (G & H in the pic), depending on whether it has aircon or not? I have aircon so does that mean it has the 3pin switch and it won't kick the fan in until the temp hits 110deg? And is item 68 the fan coupling?

I thought the fan was meant to kick in at 92deg.

Apologies too if I'm being a bit dense here. Electrics have always been a mystery to me

yes 3pin H if its got aircon

yes 68 is the fan coupling--bad labeling on the diagram.

this is assuming its a magnetically coupled fan and not a viscous one as last minute says?