Exhaust manifolds play a crucial role in the performance of your engine. The easier the exhaust gases can escape from the engine, the less back pressure is created, causing the engine to run better. Manifolds also play a part in cooling your engine. The cooling water from the engine is run through the manifold in a separate camber between the inner and outer casting. This is to keep the manifold from generating too much heat. If the engine compartment gets too hot, the engine will run poorly. Also a manifold that is too hot could cause a fire. During winterization the manifold must be drained. If not, the water inside will freeze and crack the manifold causing it to leak water externally and/or internally. We carry Mercruiser Sterndrive Manifold parts and replacement manifolds.