Phil, sleep well....

thanks for the correction re post #162 and without sounding harsh I agree with your own self description of 'nonsense' ;)

Jim

You mention that the changes (96C to 82C) were never realised - is your view based on water tests only or has someone actually compared these two models in the 974/975 engines? Or maybe you tried it in your own car?

Also by taking a look at the new clutch pictures again - fresh viewpoint in the morning, it looks as though the fins' surface area has actually increased?

Any comments on the fin redesign or purpose?

Lea

Uhm....

No input from you guys today.... :(

Here's a few calculations that suggest the reasoning for fin design. We know that silicone has a superior viscosity temperature coefficient (VTC) over other fluids so I contacted Dow Corning (DC) requesting plots. However they returned both graphs and the VTC equation :)

For their 200 FLUID range:

(I have the full pdf viscosity-temperature data sheet should anyone wish to review).

Here's the formulae:

log AV = 722.5/T + 0.000032n/T + 1.004.logn-2.447

Where:

AV = apparent viscosity, in centistokes (cSt), of fluid at any particular temperature T;

n = measured viscosity of the fluid at room temperature;

T = temperature in deg Kelvin (degrees C plus 273)


So here's where MathCad comes in (care of my good colleague John C :D ):

MathCad Viscosity Calculation.pdf

I used 200 FLUID 12,500 cSt to refill my clutch, but DC actually supply 211 FLUID to the automotive VFC industry so I thought I'd compare. 211 has exactly the same characteristics as 200 where viscosity-temperature is concerned! I suspect the major difference is purity (and cost) as the 200 is aimed at the beauty market! :eek: ;)

DegF = (DegC x 1.8) + 32

We can see that over 0C (32F) to 150C (302F) the viscosity drops from 20620cSt to 2373cSt. At ambient (25C/77F) the fluid is as sold - 12,500cSt.

So we can conclude that even though the VTC of silicone maybe far superior to alternative oils it still exhibits a 10:1 viscosity change over the typical automotive temperature working range.

What can be done to stabilise the temperature of the fluid within the VFC? Maybe by adding extrusions to significantly increase VFC surface area the rad air temperature minimises the temperature delta as seen by the fluid?

Sounds quite plausible to me...

Assuming the VFC operates as intended then the rad air exit temperature will fluctuate around (wild stab in the dark) 85C to 115C and so the silicone viscosity now changes by 5000 to 3000 cSt (1.67:1) only.

Anyone for comment?

I have had confirmation from Kanthal that this BMS isn't manufactured by them :(

However I just wanted to say a big thanks to Julian at Kanthal for his assistance - cheers.

The TB1577 is manufactured by a multitude of manufacturers as it complies with the German DIN 1715 standard, which I hope to download and review over the next day or so.

This 1715 standard lead me to this site: http://www.rau-pforzheim.com/

See attached for company references - yes Sachs AND Behr :)

Upon review of their poor product catalogue we start seeing A and Ge creeping into the part description ;-)

http://antron.pwp.blueyonder.co.uk/i...U TB1577 A.jpg

Couple this with their open reference to Sachs it's looking promising. I've emailed Sachs but no reply as yet.

I'll email G.RAU tomorrow...

Lea

"...We can see that over 0C (32F) to 150C (302F) the viscosity drops from 20620cSt to 2373cSt. At ambient (25C/77F) the fluid is as sold - 12,500cSt.

So we can conclude that even though the VTC of silicone maybe far superior to alternative oils it still exhibits a 10:1 viscosity change over the typical automotive temperature working range..."

This, by far is one of the best supported posts regarding material issue to this thread. Now for my question:
Don't you suppose the fins are there to dissipate heat generated by the friction from the viscous action of the "slipping" fan during non-engaged (general operating) times? Lets consider that if all is well, the fan will not be engaged at engine speed for the majority, nay, almost ALL the time. To me, this means for the majority of time, the fan is powered by the viscous action of the fluid as it "couples" the fan to the housing... This would, without a doubt, generate a fair amount of friction, ie heat, which would need to be dissipated to save the seals, brgs, etc of the unit. A better question of the techs would, to me, be how does the silicon oil compare to other fluids with regards to heat (friction) generation encountered by the viscous coupling of the vcf?
I believe the heat generated from friction is NOT negligible, and probably exceedes the heat encountered by the rad exit air. A good test would be to spin a vcf/fan unit at 3000rpm for a measured time(using an electric motor, or similar) and measure the deltaT of the clutch hsng (or better, the fluid if possible). I would gladly perform this experiment; however, I do not have a clutch around to experiment with. Maybe Jim or Lea could perform this experiment and let us know?

Thanks for letting me chime in...

EDITED... Well, after a second reading of Lea's last post, I guess that is what he is saying... Sorry. I did not relate stabilising the oil viscosity with controlling heat in the unit... Duh?!? After all is said and done, I think I like flexible fans more and more :D !

Walrus

An excellent thought and one maybe I didn't thoroughly consider. Maybe the fins have a two fold effect? One to remove excess heat from the silicone fluid and one to stabilise viscosity - kind of all rolled into one maybe?

I definitely agree that this friction will cause heat - but how much is the obvious question and of course the one that you have posed!?

Interesting eh?

Hi, Lea and others...

Just a note to bump thread back to top, as I am intrested if anyone could shed some light on this silicon/temp thing. When I bought my '88 560, the engine temp would hover around 80-90 in mixed driving, rarely ever going above what I would extrapolate as 90C... After I replaced my radiator (with an all-metal brass/copper unit from zeigler), I have had temp a rather consistent 5-10C higher... My initial thoughts are the new radiator is just not as good at transferring heat as the old one was (aluminum, behr unit). I've tracked down several ideas, including changing thermo, etc. My thoughts are now to replce thermostat and re-install my original radiator since I have recently replaced the tank with a new one (the water neck broke on the old one when I removed the hose to replace and service coolant).

After you guys started discussing the vcf. I began to wonder if the fan may not be coupling as it should, and watched this thread with intrest. Best I can tell, the fan/clutch is working as designed, but I have never seen it engage fully (always in slip mode), There is NO evidence of leakage of fluid, and it resists freewheeling when I spin it by hand, but I am just not sure it ever engages fully. As i have not had a chance to check it with a high engine temp (have not seen my engine above 100C where I could check it), I was intrested if I could find a way to temporarily "Lock" the fan, and try the car a few days as such. Jim's website described a way to do this, and I was about to try it, when this thread showed up.

More later...

No posts from Jim or Phil again... :eek: :(

It's a shame that Phil and Jim don't appear as regulars anymore (perhaps Phil's still suffering from ISP problems), however maybe the time has indeed come for this thread to simply fade away :( I will be somewhat saddened by this as both Jim's and Phil's views have been excellent drivers of discussion.....and of course some great humour :)

Come on Jim, surely the fin discussion will entice you back for at least a few comments?

Hi Walrus - great to see you joining in

Maybe your thermostat is coincidently failing to open fully with the new rad - maybe worth checking first before swapping the rad back?

Regarding the VFC, is it of similar type to ours - ie BMS controlling fluid from one chamber to another? Sorry not sure which model/engine/MY your car is.

If it is of similar ilk, then if you measure fan rpm it should be about 1/3 engine rpm until lock then fan rpm should match engine rpm - up to about 3200rpm or so.

I used an IR tachometer to measure mine and it's close to spec although not spot on.

BTW - didn't get chance to email G.RAU today, maybe tomorrow!

EDIT

Just heard from Phil and he's still suffering ISP issues.... hope to see you back soon Phil.

Lea

Over the last few days, I was not able to access this site, nor severl other sites, due to ISP related problems. These seem to have now been fixed.

I now have a bit of catch up reading, understanding, and thinking to do relative to the last few days worth posts that I missed. I am glad to see that this topic is still alive and kicking. I am particulary glad to see Walrus's input.

Phil

Welcome back Phil... good luck with the isp.

Yes, Lea, my vcf is very similar to yours, and back a few pages, I posted a pic from my manual with a cross-section which included a narrative on how it is designed to work. My 1988 is a 117.967 engine in a 107.048 chassis.

I'm hoping the thermostatis just weak, and I'm kicking myself for not replacing it while I was in the vicinity... rested on my laurels that the car was in good shape before, so... rolled and threw snake-eyes.

This fall I have planned a bunch of maint, so I'll get all straightened out then unless I have problems before... Thanks to all the members here, There is no shortage of info to help with my plans (timing chain, water pump, body finish, instrument overhaul, etc)... I'm kinda looking forward to it. Just gotta get some heat in my garage...

I'm not sure how to read the 'interesting' explaination that's coupled with the drawing you attached, however it does appear similar in design that's for sure. BTW the part number is 116 200 11 22 which cross references to Sachs 2100 005 032 or 043 for the tropical version - is yours the tropical version?

I see your engine/MY is destined Australia - is this correct?

Lea

Australia? No, USA (WDBBA...) and confirmed by my data card... I should have repeated that my car is a 560SL (R-107), not a 500, etc. Sorry for any confusion. Incidently, I am unclear what you mean by the "intresting" narrative? Did I state something stooooopid again???

As my car is used for pleasure/shows, etc, I am seriously considering "locking" the fan as described in Jim's website with a bolt/nut combination on the bms. I understand that will allow the fan to un-couple via the centrifugal weighted valve nside the unit, bypassing the thermal mechanism at engine rpm's above 3500... As for the increased fan noise, I may just have to live with it. I was very intrested in one of Jim's "cool harness", but according to my schematic, my fans are activated by a thermal switch, and not a resistor. I guess I could try and come up with a different value thermal switch, but I usually am running the AC so the aux fan should not be a concern.

All in all, I guess I really do not have a heating problem, just wondering what changed, and if I need to take action. I won't feel satisfied until I get the thermosat changed, but may still change the rad back to return the car to original config. Of course, I could just let my SO take over the car... Out of sight, out of mind!

Thanks for the reply...

Walrus,
In post #97, I described a current experiment based on jbaj007 to shorten the brass pin clutch and do away with the "screw and nut" idea as described in Menu#20. The object is to get it to engage around 95-100C if at all possible by shortening the pin clutch so that very little bending is needed to cause the VFC to lock-up.

As you have seen in the thread and Menu#21, the "TB1577A-GE" bms that I have does not bend until 95+ degrees C. So I originally removed 0.030" and since then I've removed another 0.050" for a total of 0.080".

For the clutch that I'm using, it appears that about 0.090" to 0.100" represents full lockup. So as it sits on the car, it doesn't need too much bending to engage (about 0.015" to 0.020"). BTW, also made the 'cut-out' of the plastic front piece (see the pictures in Menu#21 showing the "01" VFC assy.

The results are not in yet but it appears that I'm close to having this VFC works the way LeaUK does but at a higher cut-in temperature.

So hang in here and I'll report what the length needs to be in the near future.


Cool Harness: My CH will work for your car as is. You do not need to change anything. Your car as well as mine work using the CTS sensor (B10/8) and this device is a varistor; the resistance of the sensor varies indirectly with coolant temperature. If you want to see how it operates, read Menu#18.

So bottom line, my Cool Harness will work on your car.

Jim,

Thanks for the reply... I'll have to re-check my schematic on the aux fan. I. like you, thought it would work until I looked at the wiring dia. The schematic showed a dpst-type thermo-switch for the aux fan temp cut-in, but I could have easily been mistaken.

The pin idea may be a better option than the "nut-and-bolt:idea, and makes me consider a replacement pin, threaded on the outboard end with lock nuts like your original idea... what do you think?

Oh... welcome back! Glad to have your return input.

Jim,
Here is a copy of my schematic... Appears S25/5 controls aux fan cut-in/out. I could not find reference to CTS, or a B10/8 varistor in my schematic. The CIS does have a set of varistors, located on the rear of the engine for the engine controls... B11/2.

Your thoughts?

Jim's experiments of reducing the bimetal travel are indeed (in my opinion) a significant improvement on the 'thread and nut approach' and so the results will be extremely valuable for those with similar VFC issues to Jim/et al.

Sorry, I should have started with - welcome back Jim, great to see you back. I know you have still hung in there and have been following the continued discussion and so I'm pleased to see your return by post - in all sincerity.


Walrus

You say you are concerned with your coolant temperature and want to lock your fan - have you actually measured the fan rpm at lock? Bear in mind if you find it's running at engine rpm at >=100C coolent then you will gain no further improvement as the efficiency is governed by the rad at this rpm.

With reagrd to my investigations of the BMS manufacturer...

Still no reply from Sachs! So maybe time for a chaser email! If not I'll have to use my company email address - that should get a response :)

And I'll email G.RAU tonight....see if they reply.... if not it's time to flex the company email system again :)

Cheers
Lea