I have a jug of Nissan L248SP coolant mixed with 50/50 distilled water about 3-4 yrs old. Been using it to add as needed. Today I opened it (been about 8 months since last used)and there is about 1/4" of tan gunk floating on top. I shook it and it does not mix in. I filtered it through coffee filter and it is slimy tan [censored]. Car tank and radiator look fine. Any ideas what it is. I have lots of coolant stored and none have [censored] growing in them. I have no intention of using it just wondering if it will grow more, its in new clean jug. I will post pics tomorrow.