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  #46  
Old 04-24-2005, 12:22 PM
JimF's Avatar
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Quote:
Originally Posted by pberku
Here is the relevant extract from the W124 "Mercedes Maintenance Manual". Procedure No: 20-310. This is also applicable to all other Mercedes models that use this type of Viscous Fan Clutch.
--------------------------------------------------------------
"If the coolant temperature rises because of higher engine load or high outside temperatures, the air which flows through the radiator and impinges on the bimetal strip, becomes warmer.

The bimetal strip alters its shape as it heats up and opens a valve at approx. 71C by means of a pin and thus also the passage of oil from the storage chamber into the working chamber, which causes the fan to cut in.

The coolant temperature during this switching operation is between approx. 90 - 95C."
--------------------------------------------------------------
The above states that the Viscous Fan Clutch has been designed to engage at an air temperature of 71C, which is approximately equivalent to a coolant temperature of 90 - 95C. The Auxiliary fans on the other hand trigger at 100-105C. So by design, the Viscous Fan Clutch will engage BEFORE the auxiliary fans.

So Jim, if you still prefer to accept the anecdotal comments of a mechanic,, and your boiling water tests, instead of the official Mercedes technical documentation on the subject, than so be it.

Phil
. . b/c this is interesting 'stuff'! Your quote from the manual may be the 'missing-link'! Personally, I've never read that MB intended to have the vfc cut-in first before the fans for a W124. But maybe, that's why Stu was so upset.

You may want to dismiss Stu's comments but you know better than that. Calling his comments "anecdotal" [syn: unreliable, untrustworthy, undependable, subjective] is pretty harsh! Note that he said "I went through three of them, and guess what, they all worked the same way". Now I'd bet that the reason Stu was so upset was he knew the the vfc was supposed to cut-in earlier and they didn't, thus his comment, "pathetic engineering."

Now I tested two (2) vfcs and they operated the same way but mine were for the 140 car although the E500/500E vfc can/is used on the W140. At this point, I say that even though the 'intent' was there, the follow-thru to 'practice' did NOT happen!

If all vfcs cutin as you say, why did MB come out with the 'tropics' version? They didn't need to, since all are supposed to cut-in at 90-95C. If you read the referenced thread, you saw the Bong's new vfc locks up at 90C. Couldn't ask for it to be more perfect! So why the newly designed vfc??

So I do believe you and the data you have presented. Personally, it does fill in the picture because Stu 'knew' it was supposed to work but it didn't.

So summarizing what we've learned;

1. For W124, the vfc was intended to lock up at about 90-95 C water temp.
2. Tests of three (3) vfcs for the W124 show NONE of them locked at 90 and in fact it was closer to 120C coolant temp [Ritter].
3. Test of two (2) VFC bms showed bending at 100 deg C 'water' temperature but never saw them actually operate in 'air'.
5. W140 and W124 owners report that their VCs fail to engage early enough and are dependent on the aux fans.

If you carefully look at those conclusions, then you are left with the undeniable fact that vfcs do NOT operate as they were intended.

As I said before, and I quote . . "I've tried to inform you how it operates and show you "how-it-really-is" since you asked. All information is based on established facts and measurements". Note the "how-it-really-is" statement. My findings/tests with Stu's in NO way diminishes the conclusions. What it shows is that although MB may have intended the vfc to operate one way, it looks like it didn't happen.
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Last edited by JimF; 04-24-2005 at 08:23 PM.
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  #47  
Old 04-24-2005, 12:39 PM
Robert Ryan
 
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Is there an implicit assumption here that total deflection of the bms activates the fan clutch, either fully-on or fully-off? The bms lives in a stressed state on the clutch and an increase in temperature will decrease the amount of stress it can support with bending. So I'm just not so sure it's a binary thing. It might be, but has that been addressed? I can hear my fan clutch kicking in around 90 degrees, as read on the dashboard. Probing with an IR thermo has never found a spot on the radiator, thermo, water pump, or hoses above 100 degrees.

The fan clutch has heat-sink fins on it, presumably to absorb heat, which can happen through convection (radiator air) and radiation (radiant heat from the block/head).

But to go back to the poster's original problem, which is overheating, has it really been determined that the problem is in the fan clutch? Replacing this is not cheap and is not trivial, and there are lots of things that can cause overheating, such as a lean mixture, low octane gas, ring blow-by, timing advanced - and those aren't even in the cooling system. I can see how 87 octane with a bad ICV or a vacuum leak could cause overheating in traffic, and of course it begs the question, is it really overheating?
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Last edited by r_p_ryan; 04-24-2005 at 12:55 PM.
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  #48  
Old 04-24-2005, 01:39 PM
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Now I believe we're getting there.

So we all now believe MB does intend for the VFC to operate before the aux fans and in my R129 it does.

So, back to why it doesn't on the W140 and W124?

As I've previously mentioned, is the missing link the positioning of the water gauge sensor? If it's mounted on the exit side of the rad on one vehicle (R129) but entrance on the W140 we would see these temperature differences between vehicles.

Regarding the tropics unit - was it ever proved that the characteristics of the BMS were different? As maybe Sachs made other changes not visible - like changing the viscosity of the fluid to attain higher rpm when not fully locked? I just contemplating!

Lea
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  #49  
Old 04-24-2005, 02:01 PM
Marshall Booth
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Much of the discussion seems to have assumed that there is ONLY one viscous clutch and IT only engages at one temperature. Not so. There have been many models and they have been engineered to engage at different air temperatures and to remain on or shut off under different conditions..

Further the air temperature that triggers clutch engagement is NOT precisely correlated with coolant temp and while the fan MAY engage at a coolant temp in the range of 90-95 deg. C., Mercedes cautions in the M117 engine manual (20-320/5) refering to '80s engines that:

"...engine load and the driving speed play a decisive part. At low outside air temperatures, high engine load and low driving speed, the coolant temperature may increase to approximately 110 deg. C. before the viscofan clutch engages."

This makes it CLEAR that the factory was aware that the aux. fan would engage (at coolant temp of 105 deg. C.) before the viscofan under these conditions. The fan clutch used in the M119 and that Stu Ritter modified did not have the same NOT operating characteristics/set points as the fan clutch used in MY '87 diesel.

Marshall
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  #50  
Old 04-24-2005, 02:58 PM
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Looking through the Sachs parts catalog it seems there's a clutch design for every car ever made! But engine cooling basics must be common - I wonder what the fundamental differences are between clutch design and the most common reason for vehicle manufactures not to choose an existing part?

The misconception that air temperature correlates to coolant temperature in the same manor across engines, is (I think) the key .

I would be very interested to measure and compare the in/out water temperature directly at the rad.... any thoughts how this can be easily achieved?


Lea
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  #51  
Old 04-24-2005, 07:33 PM
Robert Ryan
 
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92 300e
80C at intake = 64C at exit
at idle
with IR thermo on hoses
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  #52  
Old 04-24-2005, 08:11 PM
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Lea, for your car. . .

Quote:
Originally Posted by LeaUK
Now I believe we're getting there.

So we all now believe MB does intend for the VFC to operate before the aux fans and in my R129 it does.
we don't know that yet! By that, I mean that you have not measured the temps at the heater, block, tstat area, radiator, etc. We DO know that your car shows 85C on the gauge but I can tell you that that is a VERY LOW temperature; NEVER have seen a R129 w/ M119 engine show such a low operating temp. Also does your vfc lock up?? Have you actually measured that?? Please make these measurements to show us.

Quote:
Originally Posted by LeaUK
Regarding the tropics unit - was it ever proved that the characteristics of the BMS were different? As maybe Sachs made other changes not visible - like changing the viscosity of the fluid to attain higher rpm when not fully locked? I just contemplating!
If you read the BONG36 explanation, he said it locked up at 90C. Before with the old vfc, the car was running hot. So the bms material is the difference. The 'gel' does NOT affect the pull-in point of the clutch.

So we need you to make some measurements and tell us why your engine is running at 85C.
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Last edited by JimF; 04-24-2005 at 08:22 PM.
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  #53  
Old 04-25-2005, 02:33 AM
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Jim

Yes I did read the post. What I'm wondering is if anyone has actually compared or measured the movement of the bms itself. Was the clutch to spec before he replaced it? Had it lost any silicone before it was replaced?

The silicone viscosity and volume will have an impact on locking temperature as the chamber will need less fluid to achieve full lock and so the bms doesn't 'need' to bend as much - although I suspect this has a minimal effect.

Of course my vfc locks! It's perfect in operation and meets all the requirements as detailed in MB documentation - however I have replenished the fluid with what is commonly believed to be the replacement for vfcs - 10,000-15,000CST silicone. So I do appreciate that 'maybe' my clutch isn't running exactly as the original. But, still it operates as originally spec'd.

Maybe newer clutches operate at higher temperatures and therefore don't meet the original MB doc specification anymore - that's another thought?

Maybe they all loose fluid over time?


We don't need to take measurements to understand the designer's intention regarding the vfc locking before the aux fans - we just ask them!

Also I must get one of those laser temperature measuring gadets.... and I'll have a play...

Lea
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  #54  
Old 04-25-2005, 11:22 AM
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Since you car is . . .

Quote:
Originally Posted by LeaUK
Jim

Yes I did read the post. What I'm wondering is if anyone has actually compared or measured the movement of the bms itself. Was the clutch to spec before he replaced it? Had it lost any silicone before it was replaced?

The silicone viscosity and volume will have an impact on locking temperature as the chamber will need less fluid to achieve full lock and so the bms doesn't 'need' to bend as much - although I suspect this has a minimal effect.

Of course my vfc locks! It's perfect in operation and meets all the requirements as detailed in MB documentation - however I have replenished the fluid with what is commonly believed to be the replacement for vfcs - 10,000-15,000CST silicone. So I do appreciate that 'maybe' my clutch isn't running exactly as the original. But, still it operates as originally spec'd.

Maybe newer clutches operate at higher temperatures and therefore don't meet the original MB doc specification anymore - that's another thought?

Maybe they all loose fluid over time?


We don't need to take measurements to understand the designer's intention regarding the vfc locking before the aux fans - we just ask them!

Also I must get one of those laser temperature measuring gadets.... and I'll have a play...

Lea
on the other side of the 'temperature' spectrum, it would be nice to know how your VFC locks and your temp gauge only shows 85C. Even the 'tropics' version locks around 90C, so yours appears to be an anomaly. I'm sure that has caused you to wonder what's going on?

Is it vfc locked when the car is cold?? If it is, then that would nicely explain the 85C. My tech and I 'modified' one to be a full time lock. And yes, the car's engine stayed very cool, in the 85C area.
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  #55  
Old 04-25-2005, 02:55 PM
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Hi Jim

I am wondering also and this is one of the reasons I'm still questioning all our understanding.

As I mentioned, it operates to MB spec. This means when unlocked the fan follows engine speed /2. When locked (I haven't measured the temp. of the rad), it follows engine speed until >=approx. 3000rpm when it releases. Then will lock again under around 1500rpm.

I measured the rpm by using an rpm gun and reflective tape placed on the blade housing - see here for a previous post quoting figures:

Viscous clutch/fan repair

At engagement the coolant temperature as reported by my gauge is 82-85C. The coolant will not increase over 88C - ambient temperature here at the moment is 15-20C.

I've also replaced the coolant sensor just to ensure it's reading correctly - and measured it and compared with it's quoted transfer characteristics. All OK.
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  #56  
Old 04-25-2005, 04:14 PM
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Did you replace the . . .

Quote:
Originally Posted by LeaUK
At engagement the coolant temperature as reported by my gauge is 82-85C. The coolant will not increase over 88C - ambient temperature here at the moment is 15-20C.

I've also replaced the coolant sensor just to ensure it's reading correctly - and measured it and compared with it's quoted transfer characteristics. All OK.
tstat?? If your gauge is correct, then maybe the tstat is lower temp version? If it's a 'standard' one, maybe it's stuck partially open?

A few years ago, I replaced mine (for no good reason at the time), and when I got it out, I found that it wouldn't fully close; stuck open about 1/8" or so.

I replaced it an 80C version. After that, the car's engine temp would quickly heat to temp (82C) whereas before, it would take a long time to get to temperature.

But if it's stuck open, then that might explain the cooler running engine.

Well, in any regard, if you measure the engine temps with a 'laser', then we and you will know.

I suggest that you run it at highway speeds, then go into stop/go driving and while it's still 'hot' make the measurements.
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  #57  
Old 04-25-2005, 06:12 PM
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Interesting thought about the tstat (no I didn't replace it), but I'm constantly watching the coolant gauge and so monitor it when the tstat must have fully opened - hard driving/motorway use etc... The car always reaches 80C in around 10 minutes - the time it takes for me to drive to work...

Anyway, I have found the definitive MB documentation detailing the EXACT fan operation, referencing coolant temperature, rpm and a host of other facts for the R129 and W140 engine. Here's a summary:

129 (Vfc PN 103 200 06 22) /140 (Vfc PN 103 200 02 22)
Thermostat opening 85-89C - max opening 102C
Vfc cut-in 92-100C (air or coolant temp not defined - but the doc reads coolant every where else)
Safety cut-off 4500rpm - fan speed R129 3250rpm W140 3420rpm
Aux fan (1st stage) On 100C off 95C
R129 - Aux fan (2nd stage) On 107C off 100C W140 On 115C off 107C
Aux fan 50% duty 40 second duty 121-123C
Emergency off 126-128C
Coolant temp max 130C


I have the pdf if anyone's interested.

Assumptions made:
- although MB have different part numbers for the R129/W140 and 130 (as referenced above the sachs clutch is identical
- The vfc opening temperature reference's the coolant temperature not air - I base this on that the document reference's coolant temperature everywhere else...

Now, I just guess that mine is slightly under the minimum tolerance (opening at around 85C) (also one should assume possible error in gauge) and that maybe the replacement silicone has reduced the temperature at cut in fractionally. Thus changing from it's response from 92C to 85C.

The data presented clearly shows MB's intention for the aux fans (stage 1) to nicely overlap the vfc cut-in. In my car I cannot audibly detect stage 1 (if fact I don't think I have it!) but certainly know when stage 2 operates and it does at around 107C.


Lea
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  #58  
Old 04-25-2005, 07:29 PM
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I can't be . . .

Quote:
Originally Posted by LeaUK
Interesting thought about the tstat (no I didn't replace it), but I'm constantly watching the coolant gauge and so monitor it when the tstat must have fully opened - hard driving/motorway use etc... The car always reaches 80C in around 10 minutes - the time it takes for me to drive to work...
certain, but, as I related in my previous post, my tstat did the same thing; took forever (10 mins is forever) to warm; now about 2 mins tops.

Looks like your "cool" engine has a culprit! One of the signs that a tstat is stuck, is slow warmup. Even in cold weather, the engine should warm quickly because it's a closed system and the tstat shouldn't open till the engine is at the tstat temp. If it takes a long time in cool weather, then it's most likely open a bit. Now the engine has to heat all of the coolant to get to temp. That would nicely explain the 85C readings.

. . regarding the 'specs', you can't read it since the 'tab's get removed in html. It is in a readable chart in MENU#18 for all three speeds (some models don't have three) along with the a/c pressures for aux fan activation. Can't forget about a/c.
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Last edited by JimF; 04-25-2005 at 07:41 PM.
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  #59  
Old 04-26-2005, 02:25 AM
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Blimey - surely it can't heat that quick, 2 minutes seems remarkably fast, although I appreciate that there's a significant heat source

Most cars I've ever owned take 10 minutes to reach operating temperature, none heat in 2 minutes. In cold weather the driver has also got the heating system running so it's not a closed system then.

There were no tabs to start with I will try again and make the text easier to read latter tonight.

I agree that slow heating is often due to the tstat but in my opinion the tstat is completely unrelated to normal operating temperature once the engine has reached thermal equilibrium, unless it's stuck closed/partially which will increase coolant temp above normal - are you sure your W140 is opening fully?

Can anyone else comment? I'd hate to go off topic, but (for me at least) I want to ensure my understanding is correct.

I'm soon to purchase a brand new shiny Sachs vfc, so I'll take some measurements before and after fitting and let you know what I find.

Lea
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  #60  
Old 04-26-2005, 08:37 AM
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Hi Lea,

To answer your question, here is a brief general description on how the Mercedes Thermostat works.

The Thermostat has Three operating modes:

Bypass Mode:
When the coolant is <85C, the thermostat is in the bypass mode, In this mode, in order to speed-up engine temperature rise as well as for quicker heating ability of the car's heater, the thermostat prevents any coolant from flowing through the Radiator, and diverts all coolant flow towards the car's heater. Under these conditions, the Climate Control Unit, (when set to "AUT") will not turn the Heater fan on until the coolant temperature reaches a pre-set minimum temperature.

Mixed Mode:
At coolant temperatures of >85 and <94C the thermostat starts diverting some coolant towards the radiator as well.

Full Flow Mode:
At a coolant temperature of >94C the thermostat's diverts full flow to the Radiator

Sorry, am now off to work, so the above is a very basic description.

Regards,

Phil
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Last edited by pberku; 04-26-2005 at 02:19 PM.
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