Winterizing Closed Cooling System

Winterizing Mercruiser Closed Cooling System

A closed cooling engine circulates conventional antifreeze through the block, cylinder heads and in some cases the exhaust manifolds. Sea water is pumped through a heat exchanger and then exits with the exhaust gases out through the exhaust elbows. If the system contains the recommended coolant concentration (50/50 is typical) and the coolant is still in good condition there is no need to drain the block even though this is the best time to drain and refill with fresh coolant.

However the parts of the system that are sea water cooled must still be winterized. Some Mercruiser engines have an “Easy Drain” system. It is best if you consult your owner’s manual for instructions specific to your engine in this case. If not – see below

  •         Oil, power steering and transmission coolers (as applicable)
  •         Heat exchanger (sea water side closed cooled engines only)
  •         Cool fuel (EFI engines only)
  •         Sea water pump (some engines)
  •         Manifolds (if they are sea water cooled)

Disconnect the hose from the seawater pump to the heat exchanger and connect a piece of hose (usually 1 ¼ inch id) to the heat exchanger. It should be long enough so you can put a funnel in the other end and be higher than the highest point on your engine. Slowly pour non-toxic antifreeze into the funnel until antifreeze starts coming out of the exhaust. 

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