Mercury Marine MCM 3.0L — Draining Seawater (Raw-Water) Cooled Models
Maintenance · Cooling System
For the Mercury Marine MCM 3.0L, from the Mercury Marine service manual.
Applies to: General Motors MCM 3.0L / 3.0LX engine
Before you start
- Seawater section of cooling system MUST BE COMPLETELY drained for winter storage
- DO NOT ALLOW ENGINE TO START when purging
Procedure
- Ensure engine is as level as possible for complete draining.
- Remove drain plugs from cylinder block and manifold.
- Repeatedly clean out drain holes using a stiff piece of wire until entire system is drained.
- Remove and lower hoses to allow them to drain.
- Remove power steering fluid cooler seawater hose.
- Insert a small wire repeatedly to make sure vent holes and water drain holes and passages are open.
- Crank engine over SLIGHTLY with starter motor to purge water trapped in seawater pickup pump (DO NOT ALLOW ENGINE TO START).
- Coat threads of drain plugs with Quicksilver Perfect Seal and reinstall; tighten securely and reconnect hoses.
Tools required
- Stiff wire Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Source: Mercury Marine service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.