Hi - and welcome.
You mentioned mayo water... have you spotted "mayo" in the header tank, or in the oil filler?
It is usually seen in the oil filler, but finding it anywhere is usually not good.
Can you check the oil filler too for signs?
You can sometimes get it on some cars in the oil filler and it can be down to condensation, but finding it in the water header tank IS BAD as there should never be oil in there, obviously!
You saythe head gasket is ok? How did you get it tested? The nest "modern" way to test is with a sniffer kit - uit checks for exhaust gases in the water header tank so again, if any are in there, it can only come from the head gasket leaking into a waterway.
Fans? - many people never see or hear them, so unless the temp gauge on the dash is way high, I would not worry right now.
Whats probably best is to get the water tank sniffed, and then assuming its clear, get the cooling system flushed out. A neat trick to help clean it is actually to add injector cleaner to the water.. sounds loopy, but helps clean the mayo out! Refill the coolant again... and then I would change the oil and filter, as if there is water in the oil too, then that could cost you an engine if not rectiifed.
Whatever the problem is, please dont ignore it.
David