An engine's exhaust manifold (or manifolds) is an integral part of the exhaust system. The manifold is bolted to the engine's head and is the first component that spent exhaust gasses are routed through on their way out of the exhaust system. Unfortunately, manifolds often develop stress cracks from the extreme heat that they are subjected to. As the porous metal that most manifolds are made of expands and contracts with temperature changes, cracks can occur. Below are the symptoms of a cracked exhaust manifold.
One symptom of a cracked manifold will be a visible crack that you can see on the manifold's surface. To look for a crack, look closely at the manifold, particularly where it bolts up to the motor and where the most heat will be. A large crack will be relatively easy to spot, but a smaller, hairline fracture might be more difficult to locate. You may need to remove the manifold from the engine bay to inspect the entire surface.
A cracked manifold will usually make unusual noises of some kind as some of the exhaust gasses are being forced out of the crack instead of out the exhaust. This may be more pronounced when the engine is cold and first started and can be anything from a clicking noise to a more pronounced whistling or whooshing noise. With the vehicle running, open the engine cover and listen near the exhaust manifolds to see if there is any unusual noise.
Manifold cracks can also cause excessive exhaust odours since a portion of the exhaust gasses are evacuating out of the crack instead of out the end of the tail pipe. The exhaust smell may or not be noticeable from the interior of the vehicle but will be more noticeable in the engine bay and the areas around the manifold. Exhaust leaks are potentially harmful to the health of the car's occupants.
Loss of Performance
Since the manifold is an important component of the engine's exhaust system and helps ensure that the engine receives the proper amount of backpressure (the pressure developed by the exhaust system as gasses are evacuated), a cracked manifold can negatively impair engine performance. A crack is, in essence, a vacuum leak and may prevent all of the engine functions from operating correctly.