Quote:
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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.
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"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."
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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
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. . 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.