Some of the most difficult to repair parts are the ones that must endure very high temperatures. Sure, the engine block may hit 180-220 degrees, but that is nothing compared to the extreme heat suffered by the exhaust, where temps can easily reach 1,200 degrees on a standard non-high-performance engine. Performance engines, such as supercharged or turbocharged application can get even hotter, to the point of making the headers or manifolds glow red hot. When the engine is shut off, the parts cool fairly quickly, only to be heated up once again, this heat cycling wreaks havoc on the metal, eventually leading to stress cracks.
Cast iron is very difficult to weld, it can be done, but the repairs are usually quite ugly and they don’t last very long. A proper cast iron weld require removing the part from service, pre-heating the part to near welding temps, welding the damage, and then slowly bringing the part back to room temperature. Most repair shops don’t have the capability of doing this, which is why JB Weld ExtremeHeat is such a popular product for high heat repairs.
What JB Weld ExtremeHeat Can Fix
Unlike standard JB Weld epoxy, ExtremeHeat is an air cure product designed specifically for high heat applications, withstanding up to 2,400 degrees Fahrenheit of continuous heat. This mean that your repair will last even under extreme heat conditions. All of that does come with a few caveats, however. JB Weld ExtremeHeat is not an adhesive like JB Weld epoxy, meaning it is not designed to bond two parts together; it is intended to repair cracks and holes in high heat parts.
Example number 1 – Your exhaust manifold has developed a stress crack near a bolt. JB Weld ExtremeHeat is the perfect repair solution.
Example number 2 – The exhaust manifold has split into two pieces. JB Weld ExtremeHeat will NOT mend the two parts together, this is a replacement or weld repair situation.
How to use JB Weld ExtremeHeat
Using JB Weld ExtremeHeat is easy, just four main steps can get you back on the road.
Prep – Like any bonded repair, the surface must be clean, very clean. Any debris, dirt, oil , grease or other contaminant will reduce the efficacy of the repairs. Use a chemical cleaner to remove oil and grease, and sandpaper to clear away debris and roughen up the surface to give JB Weld ExtremeHeat a good bite on the part. 80-grit sandpaper is sufficient for this job.
Cracks and holes smaller than 1/8” need to be opened up to a minimum of 1/8”. Instead of prying on the crack, use a grinder, file, drill bit, or sandpaper to open up the crack or hole.
Mix – JB Weld ExtremeHeat is a single-component putty, open the container and mix it up well until it is a uniform color and consistency.
Apply – Using a spatula, wooden stick or even your finger, apply the past to the affected area. Work the paste into the hole/crack until it is completely filled. Don’t worry about using too much, you can always sand off the excess after it has cured. Holes present a slight problem as the paste could drip through and create a little tail on the other side where you can’t reach it. If this is the case, try working in two stages- make a smaller base repair, let the paste set up, and then come back and add some more to complete the repair, keeping the back side of the hole clean.
Cure – The cure time of JB Weld ExtremeHeat is 2-4 hours for set up, with full cure in 24 hours. It is very important to give the paste a full 24 hours of cure time before putting the part back into service. You can test the repair’s completion by pushing your fingernail into the repair. If you nail goes into the repair, it is not ready. After the setup time, you can speed up the curing process with a non-flame heat source such as a hair dryer or heat gun.
JB Weld ExtremeHeat is perfect for making repairs on all manner of high-heat parts, including exhaust manifolds, mufflers, catalytic converters, exhaust pipes, engine blocks, fireplaces, smokers/fireboxes, and many more crack-prone items. It works well on steel, iron, copper, stainless steel, and most other metals that endure high heat.
Check out all the chemical products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to use JB Weld ExtremeHeat, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.