1995 c124 E320 M104.992 Viscous Fan 'turbine' noise when accelerating

[biggerhalf]

Hello All !

Since some time now my Viscous fan clutch seems to be permanently engaged irrespective of engine temperature.

When accelerating, the fan makes an awesome roar akin to a propeller plane taking off.
Funny/impressive though it may be, it's also supremely annoying and I'd swear it robs the engine of power, too.
The issue didn't always used to be there and I am convinced the engine was making more power (and was definitely way quieter) prior to this development.

I did a good amount of homework on the issue and it seems not that uncommon across many brands (not only MB).

I understand that the viscous fan clutch should engage when the engine temp is high, otherwise just make the fan 'freewheel' with the barest of friction.

I read about 'chopped carrots' test (lol) somewhere (possibly here) and attempted something similar.
After some driving I stopped and, with engine at idle and the engine temp at nominal 82-85C, I used a thick foam kneeling pad and carefully put it to the fan blades hoping I'd be able to stop the fan.
Nope - the fan would neither slow down nor stop.
I didn't apply too much force as it was obvious the fan would win.

I believe that, given a correctly working clutch, the fan should disengage at about 3.500RPM, too, regardless of engine temperature.
With the bonnet open, I gave it some gas and it doesn't look like it will.
The 'turbine' roar seems to follow RPMs, getting louder along with the revs.

With the engine off, when spinning the fan manually, it is not stuck solid.
I can spin it somewhat, I'd say it has 'a couple of blades' worth of a rotational inertia, at most.

Questions :

- If the engine temp was nominal (82-85C) and the clutch was good - should I be able to stop the fan with little effort at idle (not with my fingers, obvs) ?
- Is it possible that engine loses power with this issue present ?
- Can the fun clutch be repaired or is a new one the best way forward ?

Please advise.

Thanks !

 

[WDB124066]

1. Depends upon the temp on the bimetallic strip at the center front of the fan or more closely related to rad temp in front of the fan than coolant temp at the sensor. Try an IR thermometer...
2. Yes. It is quite noticeable together with hot trans fluid, gives you a where's my power gone thought especially in summer city traffic moving away from the lights while your AC is on.
3. The heat is making it work overtime, sometimes if you mess with it you may end up with higher engine coolant temps.

Have you had your head gasket replaced and if so do you know the brand of the one they used for the replacement...?

Other possible cause is, is your AC working nice and cool, because the low speed electric fan is switched by refrigerant PRESSURE, not TEMP. If your refrigerant pressure is low then no matter how hot the coolant gets the low speed fan may not switch on leaving the VC fan to do a lot of extra work so it locks really solid rather than a partial engagement. Check the refrigerant volume if the AC is less than ideal and monitor how long it lasts in the system at full recommended pressure when charging. If you have a leak of refrigerant it wont develop full pressure and the low speed electric fan will not come on leaving the high speed fan at 106 Deg C from memory and the VC from 95 through 104 I think, grober might be along with the proper switching temps soon, to do all the work. The VC will fully lock up before the high speed electric fan comes on. This is what you may be seeing/hearing.

You could try a new one to see how the temps and noise changes, but keep your old one and see if it is possible to return the trial one if it doesn't make a difference.

 

[biggerhalf]

Thank you, @WDB124066 - very interesting leads !

I didn't think of the impact AC system might have.

In my case :

The AC is not working at all.
It wasn't before and hasn't since I bought the car last year.
I had the system pressurised during testing and it kicked in (so I'm told the compressor is good) but a leak was also found in the condenser, so the refrigerant was removed pending condenser replacement.
I haven't yet got around to it as London is hardly hot enough for me to miss/need the AC and I enjoy/don't mind the pillarless 'windows-down' look & feel.

Consequently, I don't think the electric fans on the condenser ever come on.

Could this lead to reduced airflow through the rad and be triggering the viscous fan prematurely ?

More interestingly - yes I had the head gasket replaced early into the ownership (it was at about 90k miles, whereas I'm on 96k now) !

I was assured it was a genuine MB one (at least - I was given a choice at the time and instructed the garage to go with genuine).
The head was also machine-planed (I have images for proof).
For all I know the replacement has worked in as much as it cured the oil leak towards the back of the block and also stopped the engine 'eating' coolant.
I caught the issue early when, in my first two months of ownership I had to top up the coolant a couple of times alerting me to the issue.
(I did monitor the coolant appearance/consistency for evidence of it mixing with oil but did not see anything worrying there).
The engine runs like clockwork, especially after the recent rebuild of top and bottom harnesses and throttle body.

How would change of head gasket be of consequence to the viscous fan situation ?
I'm really intrigued as, thinking back, the fan issue was not there before the gasket replacement and only started afterwards. yet I never connected these two facts.

To be clear, too, for what it's worth :

I never had the engine overheat.
The highest temp I ever saw it reach was around 95-97C in very slow traffic during last two weeks as London was proper tropical then (35C).
Typically, no matter the weather, the needle sits solidly at 82-85C mark.

 

[grober]

This how to mod article gives further insight as to how the bimetal strip/actuator pin works [ not suggested you do this mod by the way]
K6JRF Auto Page
Sounds as if the pin is stuck [ due to corrosion? ] in the out position meaning the fan is permanently engaged. Usually these fans fail to engage due to loss of the viscous fluid rather than fault to be permanently on. You could examine the bimetal strip action on the pin and try to free it if jammed but in this hot weather and the ever present threat of GHG failure I would simply renew the unit as a matter of course.
ps these viscous fans should always be "shelf stored" in a vertical position [ in the same orientation as they are found installed on the car] to avoid damage or fluid loss ---this is always indicated on the packaging

 

[WDB124066]

I guess one way to test for this is is the fan engaged and noise heard when the engine is cold, on or just after start up...?

 

[grober]

I guess one way to test for this is is the fan engaged and noise heard when the engine is cold, on or just after start up...?

Correct --the OP's description of " 'a couple of blades' worth of a rotational inertia, at most." doesn't sound right----- Altho its often described as "locking up" its a viscous coupling not a mechanical/electro magnetic clutch so there will always be a degree of movement.

 

[wu56Shoozz]

Here's a thought for you though:

Have you listened to the Nivara Pickup OR an old Volvo 240 by any chance?? They do exactly the same at start up, they have a massive roar that settles as the car gets up to temp are you sure that its not this?

Secondly the viscous fan is inefficient and back in the day was prone to being replaced by a Kenlowe Electric fan, most Stag Owners are prone to swapping to this due to overheating issues on the car..

It maybe worth investigating this, unless you want to keep the car concours

Kenlowe Engine Cooling Fans

 

[WDB124066]

Some thoughts if it isn't a stuck pin.

MB seem to want the operating temp of the engine to rise, they do not provide the factory fit thermostat but a 2 Deg C higher one in the EPC now. I suspect they also have raised the temp by a design change of the CHG? Either that or possibly the mech who changed the CHG has allowed crud into the water galleries to block the tiny 1.5 mm to 4 mm holes in the CHG that allow water to transfer through to the head, creating hot spots?? Doesn't take much old CHG to block those holes.
If anybody has a picture of an original factory fit CHG that will help to determine if the design has changed - and especially those all important little holes.

I wonder if a rise in op temp has been done to reduce omissions?

You can buy the flush kit and do the MB recommended flush if you like, not sure it will make a huge difference TBH.

You may want to clean out the ends of the rad a lot of debris can collect there behind the shroud.

 

[biggerhalf]

Correct --the OP's description of " 'a couple of blades' worth of a rotational inertia, at most." doesn't sound right----- Altho its often described as "locking up" its a viscous coupling not a mechanical/electro magnetic clutch so there will always be a degree of movement. /snip .../ Sounds as if the pin is stuck [ due to corrosion? ] in the out position meaning the fan is permanently engaged. Usually these fans fail to engage due to loss of the viscous fluid rather than fault to be permanently on. You could examine the bimetal strip action on the pin and try to free it if jammed but in this hot weather and the ever present threat of GHG failure I would simply renew the unit as a matter of course.

Update :

Today, having started from cold, I was able to stop the fan with not much effort both during idle and whilst pulling on linkage giving it some gas.
I played with it for a few minutes whilst the engine was warming up.
It was definitely just freewheeling.
Spinning it manually, depending on push velocity, produced anything from a quarter to half turn.
It would appear, therefore, that the clutch is not permanently coupled, at least not when the engine is cold(ish).
Instead - it would appear to engage early on, as few minutes later when the temp gauge was showing 82-ish, I could no longer stop the fan.

Given today's observation - I will go with a new clutch unit.
It will be either a Behr or an MB (if not extortionately more expensive).

This how to mod article gives further insight as to how the bimetal strip/actuator pin works [ not suggested you do this mod by the way]

Thanks for that, @grober - interesting read.
I have come across this guy's articles before, too.
Quite a MacGyver
Like you said - I won't be modding anything, though.

ps these viscous fans should always be "shelf stored" in a vertical position [ in the same orientation as they are found installed on the car] to avoid damage or fluid loss ---this is always indicated on the packaging

Great reminder on storage requirements - thanks.
I did know that from elsewhere but in the light of this discussion have wondered whether the garage which replaced my Head Gasket last year did take the precaution whilst the fan was off the engine.
We'll never know
In any case, like you say - the loss of fluid would have caused the lack of coupling, which is the opposite of what I'm experiencing, so we can close that lead.

Some thoughts if it isn't a stuck pin.
MB seem to want the operating temp of the engine to rise, they do not provide the factory fit thermostat but a 2 Deg C higher one in the EPC now. I suspect they also have raised the temp by a design change of the CHG?

Great supplemental info @WDB124066 - thank you.
So far - I've not had a clear reason to touch the thermostat as engine temps behave nicely.
I don't like the thought of changing it for one which is calibrated even 2C higher, so will stick with it for as long as I can now that you said this about the new ones.

Either that or possibly the mech who changed the CHG has allowed crud into the water galleries to block the tiny 1.5 mm to 4 mm holes in the CHG that allow water to transfer through to the head, creating hot spots?? Doesn't take much old CHG to block those holes.
If anybody has a picture of an original factory fit CHG that will help to determine if the design has changed - and especially those all important little holes.

Sadly - the Head Gasket situation will remain a mystery.
I do have some images documenting the replacement process but not numerous/detailed enough to ascertain exactly whether the gasket had extra holes and/or whether the mechanic kept the channels clean/unobstructed

Is there a reliable way and/or reference results sheet to measure the Head temperature and ascertain whether it runs hotter than it should ?
This would go some way towards answering whether the Head Gasket operation was a culprit.

I wonder if a rise in op temp has been done to reduce omissions?
You can buy the flush kit and do the MB recommended flush if you like, not sure it will make a huge difference TBH.

I didn't know there's a 'flush kit' - thanks for that suggestion.

You may want to clean out the ends of the rad a lot of debris can collect there behind the shroud.

Good call.
I've actually inspected the spot for debris a couple of weeks ago when working on suspension replacements.
A couple of leaves and some dust but nothing major.

 

[WDB124066]

Your VC should not be engaged at 82 Deg C, but rather start to engage at 96 - 104 Deg C. I wonder if when the AC was de-commissioned that they had an over heat problem so put a different part number fan on your car that engages earlier, or have modded the switching strip and bits to kick in earlier. 103 200 04 22 should be your part number.

 

[biggerhalf]

Your VC should not be engaged at 82 Deg C, but rather start to engage at 96 - 104 Deg C. I wonder if when the AC was de-commissioned that they had an over heat problem so put a different part number fan on your car that engages earlier, or have modded the switching strip and bits to kick in earlier. 103 200 04 22 should be your part number.

Thanks, for that @WDB124066 .

I was there on both occasions when AC was being looked at, at least during my ownership, so defo no mods to VC then.
Also - as I stated earlier - the VC noise issue didn't used to be there for the first 6 months since buying the car, and appeared some time after head gasket was replaced last October.

I'm hoping it's just a coincidence as I dread thinking they could have bodged the HG job thus leading to temps raising.

In any case - like I said - the VC does engage early by your numbers so the first (relatively) inexpensive fix attempt will be a new Behr or MB clutch.

 

[WDB124066]

Yes, keep your old one though, just in case.

Genuine ones are not at the cheap end of the scale but may be best for peace of mind.

 

[ray_hennig]

Thanks, for that @WDB124066 .

I was there on both occasions when AC was being looked at, at least during my ownership, so defo no mods to VC then.
Also - as I stated earlier - the VC noise issue didn't used to be there for the first 6 months since buying the car, and appeared some time after head gasket was replaced last October.

I'm hoping it's just a coincidence as I dread thinking they could have bodged the HG job thus leading to temps raising.

In any case - like I said - the VC does engage early by your numbers so the first (relatively) inexpensive fix attempt will be a new Behr or MB clutch.

I've just thought of something. I had a "tropical" version of the viscous fan clutch fitted a few years ago. The result was a much more obtrusive "roar" from the fan. We've now reverted to a standard version.

SACHS 2100006243 is, I think, the Tropical version.
SACHS 2100006232 is the standard version.

And these numbers were derived from my required MB part number: A1032000422.

These part numbers are for the M104.980 engine. Yours may be different.

The ZF WebCat lists these MB part numbers, again for the M104.980:

• A 103 200 02 22
• A 103 200 03 22
• A 103 200 04 22
• A 104 200 00 22
• A 104 200 01 22
• 103 200 02 22
• 103 200 03 22
• 103 200 04 22
• 104 200 00 22
• 104 200 01 22

RayH

 

[WDB124066]

Seems the part number changes depending what chassis the engine was installed in...