W124 Overheating - Fails carrot test when engine cold.

[eyelight]

Our 1994 E280 continues to stress me out.

Hot day yesterday, inching along in traffic the temp gauge started to rise slowly, till it was over 90 and the ASR light came on, and car went into the 'limp home' mode.

Our other car, a 1994 E220 gets up to 80 on the gauge and stays there no matter what. With this E280 the gauge moves quite a bit depending on speed and traffic. Generally from just below the 80 mark when doing 50 mph on B roads, to just over the 80 in city traffic. Overly dependent on the airflow through the grill methinks. Yesterday was another matter though.

This morning I tried the carrot test with engine cold and immediately was showered in carrot purée. Fan failed at the first hurdle.

Bought this car back in February from local dealer and within a week it overheated and dealer replaced viscous fan under warranty, or at least that's what they claimed to have done. Knowing a bit more about this dealer now I'd say they just bodged it somehow. The three month warranty with the car has expired, but I wouldn't trust them to work on it now anyway.

Obviously the viscous coupling needs to be replaced. Apart from the limited access and the need for special tool to lock the fan, it looks like a simple enough job. Thanks to 230K for posting how he did this recently.

Is this likely to cure the overheating though? I'm sure flushing the radiator is something I should do as well.

Sorry for long rambling post and thanks for any info,

Larry

1994 E220 Coupé - Great car.
1994 E280 Estate - Problematic so far.

 

[Telegraph-Hill]

Carrot test....

Hi Larry,
I may wrong, but when the visco fan is coupled in a bit when cold it does not mean it is defective. Try another test. When the engine is hot > 95C open bonnet and let another person stop the engine. Watch the fan. If the fan stops immediately everything is ok, if it is running out, there is a problem with the coupling. But to my understanding you may have a problem with a blocked radiator or with the electrical Fan (if AC is fitted). If the cooling system never was maintained your cylinder head may looks like this:

Cheers,
Oliver

 

[eyelight]

Thanks Oliver,
Might get a chance to flush the radiator later this week.
Based on this post by Dave K... http://forums.mercedesclub.org.uk/showthread.php?p=10260#post10260

"Take 1 standard Euro carrot and insert the top into the fan blades. The fan should stop rotating. If the top of the carrot is sliced off, then the viscous coupling has failed in a seized state and should be replaced."

So definately the viscous coupling is in need of replacement, though later today I'll try the same test with a hot engine.
The radiator may be to blame as well. If the fan is locked or seized and so rotating at engine speed, would that contribute to overheating. Does a functioning fan rotate faster?

Larry

 

[television]

Visco fans only work at 80c + electric come in at 100, it is easy to change the visco coupling, I understand that it is cheaper from GSF but do check

 

[Telegraph-Hill]

If the fan is locked or seized and so rotating at engine speed, would that contribute to overheating. Does a functioning fan rotate faster?
Larry

Hi Larry,
the visco cupling comes in soft. If engine and coupling is cold the Visco Fan does rotate at lower revs than the engine. You can rotate the fan while engine is off very easily. If the engine is getting hotter the visco coupling comes in and the fan rotates with the same speed as the driveshaft, not faster. Sometimes older viscos seized a bit and will run in higher speed even the engine is cold. This is not a problem. But low rotating at higher temps is a fault as you loosing you additional cooling.

I don't know about the 24V versions but changing the visco fan is a horrible work as you do not have a lot of space between the fan and the radiator to fit you allan key.

Visco fans should be stored upright.

Cheers,
Oliver

 

[eyelight]

Thanks Malcolm,
GSF list the viscous coupling at £59.99 and Euro Car Parts have one at about £65. Might check Mercedes dealer later today.

So the fan is only slowly rotating when engine is cold and starts to rotate at high speed when temp rises past 80?

Found another post which talks of silicone being injected into the viscous coupling ...http://forums.mercedesclub.org.uk/showthread.php?p=144467#post144467

Possibly what these dealers did.

Larry

 

[eyelight]

Thanks Oliver,

Will try to get a chance to look under the bonnet again later today.

Larry

 

[television]

Thanks Malcolm,
GSF list the viscous coupling at £59.99 and Euro Car Parts have one at about £65. Might check Mercedes dealer later today.

So the fan is only slowly rotating when engine is cold and starts to rotate at high speed when temp rises past 80?

Found another post which talks of silicone being injected into the viscous coupling ...http://forums.mercedesclub.org.uk/showthread.php?p=144467#post144467

Possibly what these dealers did.

Larry

As Oliver says the blades do turn all the time. when cold and off the blade should not spin,it will just feel a little tight, if thats the right word.

 

[eyelight]

Yes blades can be turned by hand when engine off. Tight's a good word for it.
Anyway, I'll try and mangle a carrot with a warm engine later today, but possibly I have problems with the radiator too.

Thanks

 

[wireman]

If your fan is always coupled due to a poorly visco then it is definately not the cause of over heating, over cooling maybe, poorer fuel consumption yes, but over heating no.

A viscous coupling has a plate which is "free" to rotate inside a rotating silicone fluid filled canister, when the fluid is heated the plate is driven by the fluid which changes its state into something a bit more sticky when hot thus providing drive to the fan only when it is exposed to hot air.

Think of it as a clutch that works off heat.

There is an alternative to expensive phase change fluids, a thermostat bulb (similar to the bulb in a water stat) in the coupling closes off a small bypass hole forcing the fluid to couple the input and output shafts, which increases the coupling stiffness when hot.

Your flutuating temperature guage may be indicating the work load on the engine. It sounds like the visco may be a blind alley in your case, check (change?) the engine stat and flush the cooling system properly.

Do the carrot test when the engine is in its over hot condition, it is only then when the test is valid.

The visco fan will run at a speed less than the pulley does untill it is very hot. It will never run faster than the pulley.

 

[eyelight]

Thanks Wireman,
I think flushing the radiator and maybe the engine block too are next on the agenda and we'll leave the fan for afterwards.

Was just out at the car and ran engine till temp gauge reached 80. Fan chews carrot, and also the fan stops right away when engine is turned off, as Oliver had suggested to test.

Now to see if our garden hose reaches all the way to the street. I doubt it. Oh for the days when I lived in a house with a driveway.

Thanks all.

 

[230K]

Hi

Wireman has explained it correctly.

My advice give it a flush, check possibly remove and replace thermostat and refill with coolant.


230K

 

[Thegemmesabogie]

My experience of a 94 320TE (similar) overheating. This car was retro-fitted with aircon by the dealer before sale. When a 124 has factory aircon it also has a larger capacity radiator cos of the restricted airflow caused by the condenser. Dealer fitted aircon doesn't do this but fits an extra temp switch in the head which piggybacks the aircon cooling fan when the engine gets hot in traffic (which it does cos of the condenser). The wiring on mine had dissed itself between this extra switch and the fan.
I'm not suggesting this is what's wrong with yours but it's another avenue to explore if all else fails.

 

[wireman]

When you back flush your rad dont expect any fantastic results if the radiator is of any great age, the flow of water from a hose is quite small in consideration of the total area of pipe that you are flushing, the flow in restricted pipes will be negligible and any blockages will not be removed from severely choked tubes in the rad.

Try it and see if it improves, its the no cost option but be prepared for spending on a fresh rad.

Using a prepriatory high activity flushing agent correctly prior to reverse flushing is probably the right way to go about it.

If you do need a new rad how about getting a larger unit than the one you have at present?

Regular flushing and replacement of the antifreeze helps prevent these problems.

 

[eyelight]

Thanks to all for the advice. This evening I flushed the radiator and changed the thermostat. Fingers crossed.

The radiator in the car is not the original one, so maybe not too old. Can't find a receipt for it. Discovered a small sticker on rad saying Banco Radiator. A quick google search shows that Banco is a company in India.

http://www.bancoindia.com/radiatormain.htm
Banco is a supplier and exporter of radiators and charge air coolers to all major OEMS within India and some leading companies in Europe...
We also cater to radiator replacement and auto and car part radiator markets with extensive range of radiators covering popular German, French and Japanese cars.

Hopefully they make good products.

It's been about 7 or 8 years since I last changed a thermostat, but I was surprised there was no gasket for the thermostat cover. The parts guy at Mercedes dealer assured me all I needed was the rubber O ring, and my Haynes manual makes no mention of a gasket.

Mercedes price was £13.51 for the thermostat. Could have got one at GSF for about £8.

Whoever had last replaced a thermostat on this car had used some kind of silicone sealant around the housing. Hopefully not nescessary. No leaks so far anyway.

 

[Bolide]

When a 124 has factory aircon it also has a larger capacity radiator cos of the restricted airflow caused by the condenser

Factory aircon cars also have a fully-slotted front valance, not a partially-slotted one

Nick Froome
www.w124.co.uk

 

[MotardMan]

Eyelight, I just thought it worth mentioning that if your car has the plastic thermostat housing cover, then get the metal one for the next time you remove it. I have had the snouts break off the plastic ones in the past.... Just a thought, and prolly too late now you have done all the hard work? I hope your cooling issues are now solved!

 

[eyelight]

Follow Up

Changed thermostat and flushed the radiator last week. Thanks for the tip Motardman, but I've got the metal thermostat housing.

Anyway, on a trip into London yesterday the car behaved itself. It warms up mush faster than before, and the temp gauge goes up to about 85, where it stays, with only slight movement. No real traffic jams to speak of but a lot of stop and go city driving. The only time it rose higher and started to worry me was stopping at a traffic light, just after the long climb betwen junctions 3 and 4 on the M40. Once we were moving again, it was back to the 85 degree area.

Car needs an oil change which might help out with the cooling somewhat as well. Of course I'll still have to change the viscous coupling at some stage too.

Thanks for all the tips.

 

[MotardMan]

It sounds as if you are 99% there with this problem now, good work. Thanks for posting an update too.

 

[iamamanc]

I don't know about the 24V versions but changing the visco fan is a horrible work as you do not have a lot of space between the fan and the radiator to fit you allan key.

With an allen key you will struggle to get the torque needed. The correct tool is a snub nose socket/allen key thing (I'm sure someone knows the correct name). The special tool is a length of eighth of an inch rod bent into a letter L shape. The bottom of the L is about 1" in length. There are a couple of holes in the water pump pulley but this tool will only fit into one of them, locking it while you apply pressure to the fan bolt. The bolt could be a swine to undo but there is nothing to break so brute strength is good. It's not a hard or messy job, quite easy actually.

Cheers
Adrian