Hillsborough County schools get out May 25 for the summer break. ChaCha on! 7 years ago
Â· just now. Report Abuse. A cast iron manifold will expand and contract, the JB Weld will not. I think JB Weld is fantastic stuff (have some as we speak) but not for a cracked exhaust manifold.You can always check out their website: http://jbweld.net/index.php I only have experienced JB with cast though, if your manifold is another material you may get lucky.ource(s): Q: Will J-B Weld work on an automotive exhaust? A: Because of the extreme temperatures of exhaust systems, we do not recommend J-B Weld for use on exhaust manifolds and catalytic converters.
Similarly, rapid cooling of the catalytic converter, such as by being submerged in water, can cause the internal honeycomb structure to break apart and obstruct the exit to the exhaust pipe. If the catalytic converter becomes plugged, engine efficiency will decrease noticeably. If you are at all concerned about the performance of your catalytic converter, call into your nearest Kwik Fit for a free exhaust check.