S1 Fan/Alternator Belt

[CJD2005]

Hi All, just changed my fan/alternator belt on my S1, the old belt was 9.5mm x 1175mm. The new one although stating 9.5x1175 actually measured 10mm wide. I am now suffering with overheating 3 or 4 times on a 60 mile journey wether driving slow/fast. The electric fan cuts in thankfully but never had this on the old belt. Would the 0.5 mm make such a difference to cause this ?? It is tensioned up with 20mm deflection on the longest length as per the bible.

Any suggestions Chris

[Stwdv]

How about the weather ?