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87 745 B230FT, thermostat failed at 290,000 mi. Looking inside the head, clean aluminum, stainless parts of the T-stat- spotless but the brass body is black, it was brass colored when installed. I change anti-freeze every two years. 50/50 with distilled water.
Inside of the radiator is also black (metal / brass)
I have been using the current Prestone green which I understand may be OAT extended life stuff.
Apparently this is a chemical reaction, just wondering if it may be harmful or is it actually protecting the brass from corrosion?
Until yesterday it had not been overheated since I bought it in 1997!
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