[tucsonjwt]

While you are investigating, look for signs of green streaks from copper oxidation indicating leaking heater core, hoses, heater core nipples, etc. If you had an old engine which did not have regular coolant changes/flushing you could have junk precipitate out of the coolant and settle in the heater core over time. Rusty looking coolant can contain some big flakes of iron from the engine and fittings which can settle out in places like the heater core which don't get used for months at a time in the summer.