|
Hi Jim
I should have thought to look through your site - great pics, thanks.
However, I personally disagree with running the fan continuously as this will reduce the efficiency of the engine, increase fuel consumption and increase noise, when there is no real reason for the fan to be engaged.
R129s and I suspect most, if not all MBs with Viscous fans, are designed such that when the car is travelling in top gear the cooling system alone will maintain the optimum operating temp, ie around 85-90DegC - no fan is required. When at idle there is minimal air flow due to minimal movement and the cooling system relies on the viscous fan. The car should still remain at optimum temperature - I've tested both these conditions and my 129 supports this - Should you be in traffic then the fan clutch will engage due to engine RPM continuously changing (stop, start, stop, start) and the rad again has minimal air flow.
If your fan doesn't engage before the RED zone on the temp gauge I suspect it is faulty- sounds like lack of viscous fluid to me! The bi-metallic strip should deflect when the air flow temperature reaches around 90-95DegC which is around 85DegC on the water gauge and is significantly below the warning zone of my R129 (which is at 120DegC). As a result fluid is pumped into the second chamber causing the fan to significantly increase RPM - you should hear a whooshing sound!
The characteristics of the clutch are governed by the viscosity of the fluid within, so for correct operation below 95DegC the fan should rotate at around 1/2 engine RPM (as measured) ie there is just enough fluid in the second chamber to provide sufficient grip. At around 90DegC the bi-metallic strip will deflect and the clutch will engage - fan RPM should increase to match the engine.
Above 2000/3000RPM the clutch doesn't actually disengage but rather the viscosity of the fluid is such that is cannot maintain greater RPM. This is why the fluid plays such a major part. It governs the disengaged Engine RPM to Fan RPM ratio and the max RPM of the fan.
However my question (should anyone have finally got here) is:
Will the fan RPM increase (clutch engages) to match engine RPM if the engine RPM is already at around 2500?
The experiment I tried was to run the engine at around 2500RPM until I expected the fan to engage, but it didn't. When I reduced engine RPM below 1500 it engaged immediately. Now this could be by design as assuming the car is at greater than 1500 or so one could assume the car is in motion and therefore the rad has sufficient air flow even without the fan fully engaged. I think the only way to find out is to measure a known good clutch!!
Last edited by Learoy; 05-28-2004 at 07:29 AM.
|