i've been told that mixing the coolants can create a jello like substance. It becomes thick & if u think about the thickness of that & the blades on your water pump.. it could be really bad stress on that & being that your water pump is ran by the timing belt, you could be increasing wear via strech in the timing belt. You might wanna research this a bit more but if it were my vehicle, i'd be chaning that shit out imeadiatly!