A car’s exhaust manifold is used to take the exhaust gases from the engine to the exhaust pipe beneath the car body.
Manifolds are usually made from tubular steel, stainless steel or iron. Stainless steel is the most expensive because it doesn’t rust and lasts for a very long time, but tubular steel is also highly rated for its good gas flow.
However, most cars have cast iron manifolds because they’re relatively cheap to produce. They are heavier than steel and become brittle with age, but still last well.
Two-, three- and four-cylinder engines have one exhaust manifold because there’s only one bank of cylinders to extract exhaust gases from.
However, engines with a ‘vee’ arrangement (V6, V8 and V12) have two manifolds, one for each bank.
Exhaust manifold problems include cracks and holes, which are easily diagnosed because the exhaust becomes a lot noisier.
The manifold gasket, which sits between the engine and the manifold, can also fail, resulting in a similar amount of noise. It’s important to get these issues fixed as soon as possible, because as well being an annoyance, the engine’s performance will be affected.
An exhaust manifold gets very hot so most are fitted with a heat shield to protect other components under the bonnet.
Some manifolds are also coated with ceramic for insulation, which is expensive, or exhaust wrap, which is cheap - but the latter shortens the manifold’s life. However, most are simply bare metal.
Looking for a new manifold? Your choice includes OEM parts, aftermarket manifolds and even used manifolds salvaged from other cars.
You’ll also need to decide whether your car warrants a more expensive steel manifold or one made from iron - your decision will depend on your budget, the age of your car and whether it’s a performance model or a daily runabout.