Yes, yes I know that. I was in a hurry. Nothing is for sure. Realistically, he will end up changing his thermostat first. I'm sorry but if you have to be told to change your coolant or oil, I think there are larger problems.

Mine had yellow fluid in it when I got it, there seemed to be gloopy bits of yellow/tan snot in the fluid.
At the moment its just tap water (_plastic therrmostat housing is leaking)
Whern that's fixed I'm putting in the pretty pink stuff.
I think the mix of the two fluids made the gloopy snot stuff. My heater core was 100% clean though.