no idea on the temp, I'd think somewhere in the 130-150 range it would be open.
there were bulletins later after 68 that had the dealers disconnect the retard portion of the distributor advance and block the ports on the valve. unless you're going for originality, this valve is pretty much useless, it's an emissions thing. it also has no where to go if you don't have the dual port vac advance/retard unit on your distributor.
they discontinued the retard side because it was causing drivability issues. backfires on hard decelerations if I recall.
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