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Interesting thought about the tstat (no I didn't replace it), but I'm constantly watching the coolant gauge and so monitor it when the tstat must have fully opened - hard driving/motorway use etc... The car always reaches 80C in around 10 minutes - the time it takes for me to drive to work...
Anyway, I have found the definitive MB documentation detailing the EXACT fan operation, referencing coolant temperature, rpm and a host of other facts for the R129 and W140 engine. Here's a summary:
129 (Vfc PN 103 200 06 22) /140 (Vfc PN 103 200 02 22)
Thermostat opening 85-89C - max opening 102C
Vfc cut-in 92-100C (air or coolant temp not defined - but the doc reads coolant every where else)
Safety cut-off 4500rpm - fan speed R129 3250rpm W140 3420rpm
Aux fan (1st stage) On 100C off 95C
R129 - Aux fan (2nd stage) On 107C off 100C W140 On 115C off 107C
Aux fan 50% duty 40 second duty 121-123C
Emergency off 126-128C
Coolant temp max 130C
I have the pdf if anyone's interested.
Assumptions made:
- although MB have different part numbers for the R129/W140 and 130 (as referenced above the sachs clutch is identical
- The vfc opening temperature reference's the coolant temperature not air - I base this on that the document reference's coolant temperature everywhere else...
Now, I just guess that mine is slightly under the minimum tolerance (opening at around 85C) (also one should assume possible error in gauge) and that maybe the replacement silicone has reduced the temperature at cut in fractionally. Thus changing from it's response from 92C to 85C.
The data presented clearly shows MB's intention for the aux fans (stage 1) to nicely overlap the vfc cut-in. In my car I cannot audibly detect stage 1 (if fact I don't think I have it!) but certainly know when stage 2 operates and it does at around 107C.
Lea
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