Jim, I respectfully disagree with your statement that the Auxiliary Fan(s) have been designed to activate prior to the Viscous Fan Clutch.

The reason I disagree is that the Auxiliary fans, are large current consumers, consequently putting a great strain on the battery and the charging system, especially at low RPM's when the coolant temperature is most likely to get hot. It is precisely during this period of low RPMs (Stop and go driving) that the alternator is also taxed to its limits.

It is for this reason that the auxiliary fans have been designed as "Cooling of Last Resort", and will only activate if the Viscous Fan Clutch fails to lower the coolant temperature to acceptable levels.

Phil

You can certainly . . .
 

disagree but with me but how do you explain that the bms bend at 100C and above?? I have nothing to do with this other than making measurements. The bms was designed andf built by MB. The bms were taken from prodction vfcs. I just measured what they do.

Actually, in the "S500" class cars, the alternators are 140 amp variety. The two fans draw about 28 - 30 amps (see MENU# 18; details are shown there) to see that the fans current draw is adequately provided for with that heavy duty altenator. You certainly 'pay' for this by a decrease in gas milage but there's is not a 'shortage' of needed power.

So the bottom line is the fact that the bms doesn't 'operate' until 100C, makes it a 'later' system rather than an 'earlier' system. Sorry, those are the facts.

You said "my assumptions were incorrect", but as you see now, I made NO assumptions about when various sensors operate. These were measured by me but were designed and implemented by MB.

I'm just an user and I might add from these measurements, my Cool Harness was born. I was obvious that something was needed.

Jim

There are occasions when the auxiliary fans will come on without the VFC engaging, such as when the AC system's high pressure switch activates them on low speed.

There could also be the ODD occasion when the coolant temperature sensor, reacts quicker than the bms, but overall, the VFC has been designed to precede the activation of the auxiliary fans.

Phil

this is one of those topics that just doesn't seem to obey the 'law of physics captain' - or maybe it does but we're missing the vital ingredient.

Ah, elctrickery, this is where I come in...

As Phil explains, large current consumers at low rpm is avoided like the plague (ok apart from the rear screen heater) due to inefficiencies of the alternator. Your alternator maybe rated at 140A but that would be at peak operating rpm >=1500rpm.


I'm one for practical testing too Jim and have to say I cannot odds your test made with water and the strip. But I fear we are missing something vital as I too agree with Phil regarding MB design AND observing my own 129.

In my car, the viscous fan ALWAYS precedes the aux fans - apart from when the fluids are low in the clutch of course (but that's another story!) MB design MUST be such that the viscous fan engages before the aux fans as Phil's sound reasoning. But, your tests prove that the strip operates at 95-110DegC - in fact this temperature range is indeed the tolerance stated in MB reference data.

From discussions I've had here and what I see with my own eyes in my 129, I can only assume that there is a significant temperature difference between where the gauge sensor (and aux fan and EZL sensors) is mounted compared to that of air flow across the bi-metallic strip.

That's the only conclusion that satisfies all our thoughts, tests and observations. Or of course, maybe all gauges are inaccurate, but this still fails to explain why the aux fans operate before the viscous on the S - does the W140 have a separate aux sensor placed adjacent to the water gauge sensor as in the 129?

Jim,

Following LeaUK's response, I thought about it some more. I went back and reviewed your test procedures, that of removing the bms, and immersing it in boiling water. I believe that that reason that the conclusions you reached may not be valid are the following:

In real life the bms is attached to the fan clutch. That fan clutch is metal, actually I think its Aluminium, hence the clutch will get hotter, stay hotter, and will do so much faster than the surrounding air that heats it. For that reason it will also cause the bms to bend much faster than if you were to just take the bms out and test it in boiling water.

More significantly, in real life, the bms is FIXED at both ends to the fan clutch, and can not elongate, hence any heating effect will cause it to arch-up in the middle. This arching-up (bending) is what causes the fan clutch to lock-up.

If you just remove the bms, and put it in hot water without affixing its ends, it will elongate before bending. This is not the desired results that you need to activate the clutch. The bms needs to arch-up.

Phil

I can't discuss this any further . . .
 

if you won't accept facts that are presented, then I will never convince you. Ohms laws is a fact, and it doesn't change because you "THINK" it's not correct. You have taken a postion that is untenable even when shown the way it operates.

The highleighted area in red is a good example: There is all forms of inertia; the most common is motion. It hard to get going initially when riding your bike until you "get-going". This 'get-going' is you overcoming ineritia. It gets easier to 'pedal' the bike.

What we have in the body of the vfc is thermal inertia and it is the same. It takes considerable amount of heat to raise the temp of the large aluminum block. So it takes considerable amount of heat for the block to get to temperature. So that would act to RETARD any bms bending operation. Fortuantely, the bms is mounted so that it barely contacts the alum body.

The BMS itself is mounted so that it touches the alum housing in three spots; one on each end and the pin clutch. The 'surface' area of these three spots is probably less than 1% of the bms' surface area. Thus the bms is almost suspended over the pin clutch. It important that it NOT contact the body of the alum housing since then the heat will be 'sunk' into the housing and delay, require more heat, to the bend the bms.

Air is the 'medium' which the bms uses in normal operation. When the bms is immersed into this medium it will respond when the temp of the medium is raised to the point of bending. So too with water: it's another medium which was heated homogeneously until the bms started to bend. If anything the water medium is more condusive than air since it's MUCH easier to maintain a homogeneous temperature throughout the vessel by gentle stirring. So the water experiment was and is valid way to test the bms to determine where it bends. There's NO difference.

When the bms is 'cold', it is 'straight' and it depresses the pin clutch so that the vfc action is bypassed. As it heats, it bends and then releases the pin clutch so that it becomes a full-time fan until the engine rpm of about 3200rpm, the gel is forced back into the 'bypass' chamber.

You have never even looked at one, held one, took the cover off, etc. but yet make statements about how it operates not even knowing anything about the unit - - - and - - - you offer science fiction as an explanation.

You said, the metal clutch will get hotter, stay hotter, and will do so much faster than the surrounding air that heats it.. So let's try an experiment with a large and small METAL item; a beebee (bb) and metal bowling ball.

So if we dropped both items in a large bucket of water at 150F, the metal bowling ball would heat much faster than the bb and be hotter than the bb. All I can say is I wouldn't want to live in your world!

I've tried to answer your questions with scientific facts but now we are into areas that add nothing to this thread.

Jim, you state the following:

"You have never even looked at one, held one, took the cover off, etc. but yet make statements about how it operates not even knowing anything about the unit - - - and - - - you offer science fiction as an explanation."

Jim, your above quoted statement, is wrong, and totally unfair. I was examining, and holding my old VFC in my hand while corresponding with you. (Mercedes Part No: 6032000022 Manufactured by BEHR)

In any event, I do not wish to continue this debate with you. I can't follow some of your rationales, and now your statements, and I suppose as a result, now some of mine as well, seem to be degrading to personal attacks.

However I do agree with you when you state that "we are into areas that add nothing to this thread".

So let's leave it at that for now.

Phil

A big problem is that it's NOT been kept entire clear what temperature is being discussed. The viscous fan is engaged when air temp exceeds a perticular value (the value differes from engine to engine and even by year) and AIR temperature doesn't precisely track with coolant temp. At an air temp of ~70 deg. C., coolant temp is usually 95-100 deg C (according the the W126 workshop OM603.96 engine manual) but that isn't always the case - say when driving at high speeds at temperatures below zero F. or in slow stop and go traffic on a humid 100 deg. F day. It's NOT always clear in the Mercedes manuals whether they are discussing air or coolant temp when temperature is referenced, but the viscous fan is triggered by the temperature of the bimetaic strip and that's most profoundly influenced by air temperature - NOT coolant temperature.

The aux. fan is triggred at coolant temperatures between 100-110 - again depending on year and engine. If the car has been shut down for 5 or 10 minutes on a HOT day and then the ignition turned on, often the aux fan will come on IMMEDIATELY - I believe even before the engine starts (not warm enough to check right now).

Under MOST conditions (excluding factors related to AC operation) the viscous fan will engage sooner than will the aux. fan, but NOT always.

Marshall

Here's some comments by . .
 

by Stu Ritter. He's was the technical editor of the MBCCA's "The STAR" periodical, and former MB shop-owner (35+ years experience), on overheating M119's and modifying the viscous-fan cut-in. He has since published a book with antedotes and fixes.

Here is his words regarding the operation of MBs vfcs.
----------------------------------------------------------------
The problem is the viscous coupling. I've done a lot of work here to get my car to run cool. Now, with 95 degrees in Denver and full tilt A/C running, I'm staying under 90C. Actually, it only goes up to 90 when I'm idling for awhile at a stop. It stays at thermostat most of the time now.

I was seeing 115-120 under these conditions. I found that the viscous coupling wasn't working as it should. I went through three of them, and guess what, they all worked the same way.

I discussed this with the chief MBUSA engineer. He said that is the way they are supposed to work. The fan clutch wouldn't engage until the strip saw 107C which really meant 110C air going through which meant the radiator saw 115-120C. If you listen carefully to the fan you will see how quickly it cuts out. It only locks on when you get up around 120-125C which is really bad. This little mod takes care of the problem and counters the factories pathetic engineering.

I took the viscous off the engine. You can carefully remove the bimetallic strip which has the pin attached. Drill a small hole (say 4mm) and thread it (say 4mm). Get a little 4mm bolt with two nuts. There isn't enough thread on that thin strip to trust the threading. Screw the bolt in and double nut it, one on each side of the strip. Bow the bimetallic strip around 1mm. This will give you full tilt fan engagement right up to the high speed disconnect around 3,200 rpm. You won't believe the amount of fan noise. It's noisy but the engine runs cool as a cucumber. For winter, I reach down with a 4mm wrench, loosen the nuts, back out the bolt the 1mm and have a normal (ha ha ha) viscous coupling during the winter when I don't need the fan howling all the time.
--------------------------------------------------------------
The last part highlighted in blue, is the modification to the vfc which is described on my web page in detail in MENU#20.

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. I'm sorry that you refuse to accept these facts but it is your loss.

ok, this is a topic that has mystified me for several months. i have modified my bms, bent it this way and that and i cant seem to find a happy medium between engagement and non-engagement.

can the bms be purchased separately? like say a 'tropics' bms? this would seem much more worth while than tapping screws and such. i read the w124 owner's bible and was not all that impressed with this modification. i don’t want my vfc running all the time, if i wanted that i would just bend it out (or take it off!). plus, having the vfc run all the time will lower fuel economy. i just want the vfc to come on at 92-95C, and go off at 82C, very simple. is that too much to ask? :confused:

Jon,

If you're in my neighborhood some day (L.A. westide), and have your viscous fan clutch in your hand, come by and I'll modify it for you. I drill and tap a very small hole in chamber #1 and fill with 10.000 cst silicone oil (Toyota). Then I seal the hole with a headless Allen screw.

When filling with a dental irrigating syringe, I remove the BMS, and the pin that the BMS acts on is pushed out by the filling pressure. A light touch with the Dremel and I shorten the pin ~ 1 mm. and re-insert it. This causes it to engage at a lower temp. Replace the BMS and you've made a "tropicalized" Mercedes fan clutch.

FWIW.... please, no one get in a snit...no panties in a bunch...it's just that it's worked for me. I'm sure there's other better techniques out there, but it's easy and it works.

I did a little . .
 

searching for the "tropics" version of the vfc. It was three (3) years ago but it's a good thread.

You need to buy the complete vfc but the prices in the tropics were very reasonable as I remember. Anyway, read it and see for yourself. BTW, it's the ONLY one that works below 100+C.

If MB older vfc versions worked below 100C, why would they have to make this version? That was a rhetorical question, I know the answer! If you have been following this thread and have read the link below, now you also know.

http://www.peachparts.com/shopforum/mercedes-benz-performance-paddock/43792-high-engine-temps-solved.html

Jim, Could not resist, I am back,

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 you like I can E-mail it to you.

--------------------------------------------------------------
"The Viscous fan coupling is a maintenance-free hydraulic coupling which operates steplessly dependent on temperature.

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
--------------------------------------------------------------

Jim, 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.

Phil

Jim, Could not resist, I am back,

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 you like I can E-mail it to you.

--------------------------------------------------------------
"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
--------------------------------------------------------------

Jim, 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 anecdotal comments, and your boiling water tests, instead of the official Mercedes technical documentation on the subject, than so be it.

Phil

My turn!

I have to reiterate the point about my R129 - the viscous fan WILL engage before the aux fans under 'normal' running condition. This is FACT and how car manufactures design cooling systems, this is also fact - I have several collegues who design for the UK diesel engine branch of Ford.

The MB manual could be incorrect and so we shouldn't dismiss this and of course that different engines have different cooling requirements/characteristics.

The W140 mentions 71degC but MB data for the R129 this isn't so. Of course (as previously mentioned) occasionally it's unclear as to which, coolant or air temperature, is being referenced.

Several FACTS have been presented in this thread and some of which appear contradictory, so it's important to 'step back' and look at the 'bigger picture'. Facts are indeed facts, however when one steps back it allows a non-blinkered view such that all those presented can be considered before making sweeping judgments.

Let me summarize the FACTS:

1. The VFC bi-metallic strip, Jim tested, operates at around 100DegC air temperature
2. In Jim's W140 (as standard) generally the aux fans operate before the VC
3. In Lea's R129 the VC (in 99% of cases) operates before the aux fans and under 'normal' driving conditions (urban/motorway/stand still)the coolant gauge never exceeds 85DegC
4. Over time, fluid will leak from the VC changing it's characteristics
5. Manufacturers design the cooling system such that the VC operates before the aux fans - whether this is finally achieved is another matter
6. No two engine codes are identical in cooling or performance requirements
7. W140 owners report that their VCs fail to engage early enough and are often dependent on the aux fans - I haven't heard of this issue on the R129.
8. VCs can be modified to operate at a lower temperatures

I guess I've missed some, so please add or disagree. We need logical rational from a variety of skilled sources to try and resolve the 'actual' characteristics and to resolve this issue once and for all!


Lea