This manual covers Mercury MerCruiser marine engines, specifically detailing the In-line 4 Cylinder, 3.7L (224 CID) models. It provides comprehensive information for various serial number ranges across models such as MCM 170 MR, MCM 170 ALPHA 1, MCM 165 ALPHA 1, MCM 3.7L ALPHA 1, MCM 190 MR, MCM 190 ALPHA 1, MCM 180 ALPHA 1, and MCM 3.7L LX ALPHA 1. Designed for reliability and performance, these engines are engineered for demanding marine applications. The purpose of this manual is to serve as an indispensable resource for maintaining and repairing your Mercury MerCruiser engine. It includes detailed instructions, high-definition diagrams, and well-structured content covering general information, maintenance, troubleshooting, removal and installation procedures, engine mechanicals, starting and ignition systems, charging systems, instrumentation, wiring diagrams, fuel systems, carburetors, cooling systems, exhaust systems, and power steering. This guide is suitable for both professional mechanics and users with limited experience.