Jim
Thanks for your reply.
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but the answer to your question . . . . Will the fan RPM increase (clutch engages) to match engine RPM if the engine RPM is already at around 2500? . . . . is No!
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According to many posts made in other forums here, the majority say it's around 3000RPM and from my own testing this seems true - although I've replaced the viscous fluid so the original performance may of changed - and that I appreciate.
So, why doesn't the clutch attempt to
engage at higher than 1500RPM ? I suspect it's because the fluid is thrown such by the centrifugal force - it cannot enter the correct chamber to increase fan RPM - what's your thoughts?
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But you are incorrect re the temperature at which the vfc engages: for the W140 and W129 cars, it's very high, as I said, about 110degC. One could ask, why bother since it's already a bit late!
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I would be very surprised if Benz designed a system that was so poor, but I have no experience of other than my R129 clutch, so I take your point. My 129 engages at water temp of 85DegC, which (without measurement) I suspect is around 95C air temp accounting for the mass of the engine and coolant channel. No changes to the bimetallic strip have been made!
Don't forget that the strip operates on
air temp not water temp, and there will always be a substantial difference between the two. Also, if your clutch fluid has begun leaking out then the performance will be significantly affected causing the effects you have witnessed. A reduction in clutch fluid is VERY common for any viscous clutch for any car!
My plan is to measure a known working clutch as I see this the only way to confirm correct operation - unless I talk to the designers of course!!
Lea