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Thank you for the link!
I had the same contamination in coolant tank of my 98 Chevrolet Malibu with 3.1l V-6 engine. I would say even much more pronounced.
Recently asked for coolant system service at my local Firestone, because of the sediment and because I had to add a quart of 50/50 DexCool solution every tree months. Was not sure if this is an evaporation or small leak, even more that the Malibu manual states it is normal to add coolant up to four times a year.
The mechanic told me DexCool does not need be replaced before 100-150,000 miles. I told them about the need to add coolant. They started from pressure test and found a leak on the top surface of the intake manifold gasket. Now the car is in shop, undergoing the gasket replacement.
Had the the reddish sediment in the coolant tank from the very beginning, when I bought the car used with 15k miles. Serviced it first at dealer, than at a very good local Firestone shop after the original warranty expired. They added coolant every 3 months. But nobody told me before this sediment is not normal.
The contamination looks natural with the orange DexCool coolant: the iron oxide, i.e. common rust, have practically the same color, only more dark Most probably, even certified mechanics may not know this is tell-tale sign of rust.