The life expectancy of a Chevrolet exhaust manifold should be the life of the vehicle's engine. This is the part that the extremely hot gases from the combustion chamber travel away from the engine and into the exhaust system. The only reason for a failure of the exhaust manifold to malfunction on a Chevrolet is for it be become cracked. It is a rare occurrence but can possibly happen. The exhaust manifold can be cracked if subjected to an extreme temperature change over a very short period of time. This can happen by a Chevrolet owner washing their engine when it is still very hot. The cold water can crack this part if this procedure is done reportedly. The Chevrolet exhaust manifold can also become cracked if it is dropped when a valve job is being done to the car in the shop. This would be the failure of the technician doing the work on your vehicle. This cracking of the exhaust manifold can also be caused by your engine overheating for a prolonged period of time. For most car owners, they will never have to worry about this part for the lifetime of their vehicle. The last reason for an exhaust manifold to be replaced is if the car owner desires for better flow from the engine. This is when a header is installed replacing this manifold. This was very poplar on Chevrolet models back before the smog devices became mandatory on vehicles in America. Today, it is almost unheard of because of the added expense of modifying a header so your car will be street legal to meet the required US Government mandated smog emissions testing.