Auto Systems and Repair: Exhaust Manifold Replacement
Exhaust manifolds are subject to extreme heat, which may cause them to warp or crack, necessitating their replacement.
Exhaust manifolds should be checked periodically to ensure they are free from cracks and that the exhaust hardware and heat shields are secure.
A cracked or warped exhaust manifold should be repaired immediately. The exhaust manifold is attached to the engine by simple studs and nuts. However, access to the attaching nuts can be very limited, sometimes requiring dedicated tools such as "S" and "U" shaped wrenches or swiveling sockets. After the manifolds attachment to the engine is removed the exhaust manifold itself must be withdrawn. Some vehicles offer no room to achieve this, in such cases the engine can be shifted in place to increase space as needed. In contrast many vehicles offer plenty of room to perform this job, making the removal and replacement of the exhaust manifold very straight forward. In either case, the manifold gaskets as well as the removed hardware, i.e. nuts, bolts, washers, and studs should always be replaced with new parts.
Mechanics Corner: More Technical Detail
- The exhaust manifold is the first downstream emission control device. The purpose of the exhaust manifold is to gather the extremely hot exhaust gases from the individual cylinders and channel them into a single header pipe while keeping them as hot as possible. Some exhaust manifolds are heavy cast-iron devices designed to store the extreme heat caused by the still-burning exhaust gases leaving the individual cylinders. This helps sustain the combustion burning process into the next downstream emission device, the catalytic converter. The exhaust manifold is bolted directly to the engine cylinder head.
- Because the exhaust manifold is subjected to such extreme heat, it has a tendency to crack or become warped. In addition, the fastening bolts and studs tend to break from the constant expansion and contraction caused by the punishing heat; this leads to exhaust leaks. In some cases, the exhaust manifold is an integral part of the catalytic converter, so they must be replaced as a unit.
- To replace the exhaust manifold, remove it from the cylinder head and disconnect it from the exhaust header pipe. RepairPal technicians don't recommend attempting to resurface a warped exhaust manifold because it will soon crack. Always replace all of the fasteners and gaskets when performing this repair so the new bolts will torque properly and the new gaskets will seal. Always make sure to clear any dust or debris from all the mating surfaces on the cylinder head and header pipe so the new manifold won't leak.