Draining the Seawater System

Between the years of 1998 and 2001 Mercruiser decided to target the market regarding marine engine draining with specific focus towards making this step easier for the consumer. The thought behind this was that making the process of draining the engine more simplistic had the possibility of lengthening the boating season in areas such as the Midwest where cold weather normally precedes the actual winter months by several weeks if not months. This decision was a delicate balance for Mercruiser due to the fact that a large portion of their dealer network is located in areas that cannot boat year round and therefore these dealers look to the winterization process as a revenue stream leading into the slow winter months when their service departments really slow down. The other major concern was that by introducing a drain system opened the possibility to freeze damage being pointed back at Mercruiser. With the current process of manually removing plugs the customer is ultimately responsible to verify that the coolant drains once the plugs or hose is removed. However with a drain system means any given drain line could plug individually and therefore the customer would not be able to determine if a specific individual component had drained properly.

Therefore Mercruiser developed and patented a variety of drain systems that essentially function the same however offer a different means of activating the drain depending on the complexity of the actuation design.  The drain system functions by connecting all of the required drain points into a single manifold for draining. However the drain points all incorporate patented features that prevent them from plugging with debris. The below article and video walk through Mercruiser’s manual single point drain system.

**CAUTION**

Water can enter the bilge when the drain system is open, damaging the engine or causing the boat to sink. Remove the boat
from the water or close the seacock, disconnect and plug the seawater inlet hose, and ensure the bilge pump is operationall
before draining. Do not operate the engine with the drain system open.

IMPORTANT: Only drain the seawater section of the closed‑cooling system.
IMPORTANT: The boat must be as level as possible to ensure complete draining of the cooling system.

Your power package is equipped with a drain system. Refer to Drain System Identification to determine which instructions apply
to your power package.

IMPORTANT: The engine must not be operating at any point during the draining procedure.
IMPORTANT: Mercury MerCruiser requires that propylene glycol antifreeze, mixed to the manufacturer’s instructions, be used in
the seawater section of the cooling system for freezing temperatures or extended storage. Make sure that the propylene glycol
antifreeze contains a rust inhibitor and is recommended for use in marine engines. Be certain to follow the propylene glycol
manufacturer’s recommendations.

Drain System Identification

Manual Single‑Point Drain System Boat in the Water

1. Close the seacock (if equipped) or remove and plug the water inlet hose.
2. Rotate the blue handle counterclockwise until it stops (approximately two turns). The red on the handle shaft indicates that the drain system is open. Do not force the handle as this will create new threads.
3. Immediately remove the blue drain plug from the side of the thermostat housing. This must be removed within 30 seconds to properly vent the cooling system.

4. Visually verify that water is draining. If water does not drain, remove the blue drain plug from the distribution housing and drain manually.

1. Allow the system to drain for a minimum of five minutes. We recommend leaving the drain system open while transporting the boat or performing other maintenance.
2. Reinstall the blue drain plug in the thermostat housing.
3. Close the drain system by rotating the blue handle clockwise until it stops and install the blue drain plug, if removed. The handle is fully seated when no red is visible. Do not overtighten the handle, as this action will create new threads.
4. Open the seacock (if equipped) or unplug and reconnect the water inlet hose before operating the engine.

Boat out of the Water

1. Place the boat on a level surface to ensure complete draining of system.
2. Rotate the blue handle counterclockwise until it stops (approximately two turns). The red on the handle shaft indicates that the drain system is open. Do not overtighten the handle, as this action will create new threads.

3. Visually verify that water is draining. If water does not drain, remove the blue drain plug from the distribution housing and drain manually.

1. Allow the system to drain for a minimum of five minutes. We recommend leaving the plugs out while transporting the boat or performing other maintenance to ensure that all water is drained.
2. Close the drain system by rotating the blue handle clockwise until it stops or installing the blue drain plug. The handle is fully seated when no red is visible. Do not overtighten handle, as this action will create new threads.

Buy the products and parts you need...