the transmission oil cooler runs through the side tanks of the radiator.
How does the transmission oil look?
Look inside of the radiator and see what the condition is in there. The tube could be all clogged up .
If your coolant is black it must be contaminated with something.
my uncle claims once an engine over heats and the inside of the coolant passages in the engine block are scorched your coolant will look like mud after a few days of driving.
Of course if this Eldo has grown acustom to running with this junk in the cooling system, run it as is or till a major problem arises.
========= Harryface =========
1991 Pontiac Bonneville LE ~_~_~267,300 miles_~_~_