Mercury - Exhaust Manifold Exhaust System Cast Iron Marine Finish 866178T01. Overview. When you've spent enough time on the water, you start to appreciate the parts you rarely see but depend on every single outing. The exhaust manifold is one of those unsung heroes - it keeps the engine breathing cleanly and running cool, day after day, season after season. With Mercury Marine part number 866178T01, you're getting a piece of hardware that feels solid in your hands and even more reassuring once i