Pliobond (the best) keeps its integrity and stays adhered at 400 F. Darkens & hardens at 450 to 500F and loses integrity at 500 but still stays in place and when its cooled it remains adhered to the metal.
Permatex copper “spray a gasket” high temp – starts smoking and loses adhesion at 400 F but stays in place and is still adhered when cooled.
K&W “Copper coat” brush on gasket sealer – loses adhesion at 400 F but stays in place and is still adhered when cooled.
Silicone sealer resists heat up to 500F, starts to fail by 550 and loses its adhesion. Does not harden but has mediocre oil resistance. Silicone leaks oil as a head gasket sealer.
Permatex “Ultra” silicone based oil resistant gasket maker loses adhesion at approx 500F and fails. Minimal hardening. Silicone leaks oil as a head gasket sealer.
“The right stuff” by permatex failed in a Norton as a head gasket sealer.
Hylomar AF stays gooey – non-hardening and no adhesion but good to 500 deg. Aerograde Hylomar is semi hardening and has some adhesion after drying and is good to about 450 but looses adhesion around 500 and has poor adhesion compared to pliobond at all temps (worse at 500 deg where it loses all adhesion permanently).
Wellseal stays gooey – non hardening and has no adhesion, starts smoking at 400 and turns to water consistency at 450F.
Gasgacinch Weldwood and Barge contact cements burned black & hardened before pliobond and lost their adhesion at lower temps around 400F.
Permatex motoseal 1 grey (same as popular Yamabond 4) bubbled at 400F and hardened but did not lose its adhesion. Became very brittle but was still adhered when cool.
Yamabond 5 (clear contact cement) bubbled at 400F burned black, became brittle and lost adhesion.
Permatex high tac turns to liquid, smokes and loses adhesion at about 350 F.
Silver and copper paint gets soft and loses adhesion around 350F
Permatex formagasket starts smoking & bubbling and fails at 250-300F.