Temperature is irrelevant- - - -what you need is exhaust gas volume to push the flap open once the spring tension relaxes. Unless you're willing to rev the engine up to highway cruise speed in the shop,
THE
VALVE
WILL
NOT
MOVE!

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!