Cooling system , fluid condition

The radiator for some models has a transmission fluid cooling system built into the radiator. There are fluid lines (tubes) that run from the transmission to the side of the radiator. This system may have a leak internally into the coolant system via the radiator. Without seeing a picture of the coolant this is my best guess.

Check your transmission fluid level to see if it is low and see if it is also discolored.

Check your engine oil to see if it is discolored. If the engine oil is "milky" then coolant is leaking into the oil system. Sometimes through a head gasket port that has blown.

It can also be condensation build up over time depending what type of climate you live in. But that is a hopeful prayer.

Best to get a mechanic on this one.

-F