2011 535i xDrive, 110k miles, all original water pump, thermostat, fan, battery. Fan is coming on intermittently on low speed after 10 minutes warm up with the heat is ON. Fan does NOT run when heat is turned low. Tested the water pump using the bleed procedure and it does run at various speeds in the 10 minute bleed cycle. I wonder if the old battery (i.e. occasional low voltage over night) may be the problem, or if the water pump is dying at low speeds. Suggestions to test further?