J-B Weld can withstand a constant temperature of
500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes.[9]
OK, but still not high enough for exhaust temps.
From
J-B Weld's SiteWill J-B Weld work on an automotive exhaust?
Because of the extreme temperatures of exhaust systems, we do not recommend J-B Weld for use on exhaust manifolds and catalytic converters. Nor do we recommend the product for repairs within the combustion chamber. However, in areas where the continuous temperature is less than 450º F, we do recommend our HighHeat epoxy putty stick.
