Although a cracked exhaust manifold does not directly cause danger, it can indirectly be dangerous, as the issues it causes makes a car unfit to drive. Effects include increased engine emissions, poor vehicle performance and damage to an engine's components.
The exhaust manifold is an essential part of a vehicle's emissions control system. According to the California Bureau of Automotive Repair, the exhaust manifold is used to burn unspent fuel that would otherwise pass through a vehicle's exhaust system. Cracks in the manifold can result in unsafe levels of emissions from a vehicle's exhaust and may result in damage to an engine's valves should they come into contact with cool air.