Join Date: Jul 2000
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With respect to corrosion (iron engine block and iron exhaust manifold), you need the engine to develop full operating temperature (180°F/82°C) for a period not less than ~1 hour. This will 'convert' the developed destructive ferric (red) rust to 'protective' ferrous (black) rust.
Obviously, you cant look inside an engine's cooling passages to assay the amount of 'red' rust present; so, the advice of 'running the hell of the engine at the earliest opportunity' ... is a good one.