Exhaust manifolds do many different jobs (depending on application): Transporting extremely hot exhaust gases (up to 1400 F) from the cylinder head to the exhaust piping; Providing mounting for Oxygen sensors, A.I.R. piping, and EGR piping; Sealing the engine head and exhaust piping to prevent fumes and noise from escaping the engine compartment.

Why do Exhaust Manifolds fail and what happens when they do?One of the goals of today's car manufacturers is to design lighter vehicles to boost fuel economy. To that goal, the Manifold design trend since the late 1970s is to reduce weight and make a thinner, weaker Exhaust Manifold that is more prone to cracking than in the past. This design trend along with leaner fuel mixtures, lighter weight OEM castings, welded tubular steel Manifolds, an aging vehicle population and normal wear and tear has created a climate where Exhaust Manifold failures are increasing daily.

Exhaust Manifolds can fail for some of the same reasons as any other type of exhaust part. Heat, thermal stress, and corrosion can produce cracks that result in leaks and noise. When a manifold fails there is a pulsing noise ranging from a soft ticking to a loud booming depending on the size of the leak. The hot gases can burn nearby wires and hoses, causing additional damage. Additionally, carbon monoxide vapors may find their way into the passenger compartment with potentially deadly results. The Manifold must be replaced when it fails.