There are quite a number of high temperature paints available. However, my pipes are old and already rusted and rough. That is why I was thinking about the POR-20.

On my R107 manifolds, I first degreased, then treated with a phosphoric acid type rust converter. Washed that with water after drying and then applied POR15. Very good long term results.

Not sure if wood stove/bbq paint or the like would work as well at preventing rust from coming back. same for some of the other paints like this one, which might work better on new pipes.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5