How to Fix a Leak in an Exhaust Manifold

by Jack Hathcoat

Exhaust manifolds are subject to intense heat. Over time, the constant heating and cooling of the metal causes the manifold to distort and warp causing gasket leaks. Eventually, if the manifold is lacking in metal content due to factory compromises for overall engine weight, the manifold cracks. Cracked manifolds are easily detected because the crack expands as the engine heats and the exhaust noise gets louder.

Replace defective gaskets or seals. Use a socket wrench and wrench set to remove the manifold. The "doughnut" gasket seals the exhaust pipe connection to the manifold. This gasket is subject to lots of movement and contains carbon to act as a lubricant. Over time, it wears and needs replacing.

Inspect the flange where the manifold bolts to the engine. If there was not a gasket when the manifold was removed, this is normal. The factory depends on perfectly flat surfaces mating to each other. If a leak has developed, have a professional machine shop resurface the manifold face. Use an aftermarket gasket in conjunction with the resurfacing. Even though the manifold is in good shape, the mating surface on the head may be damaged. The new gasket will correct this issue.

Remove cracked manifolds and have them repaired, or replace them with a new part. Expensive manifolds with minor cracks are often welded to fill the breaks. This process requires preheating the manifold in an oven, then welding with specialized equipment. Although not inexpensive, it is the least expensive option for high-end vehicles with high-priced parts. Reinstall the manifold after the repairs are completed.

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About the Author

Jack Hathcoat has been a technical writer since 1974. His work includes instruction manuals, lesson plans, technical brochures and service bulletins for the U.S. military, aerospace industries and research companies. Hathcoat is an accredited technical instructor through Kent State University and certified in automotive service excellence.

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