when my w124 88 reaches operating temp between 80 - 90C it runs wonderfully but will sometimes climb over 90, i don't know what the temp must be before the aux fan starts but I have'nt seen it operate in years! it however does work becuase when the aircon is on it starts, does this fan come on only for the aircon or also incase of overheating? if so what temp triggers it and how can I check its working?