To winterize my 1991 4.3 LX fresh water cooled Merc I/O engine I remove the thermostat housing and fill the engine block with -60°f antifreeze. It only took 5 or 6 quarts to fill the block. Is this the capacity of the engine block? Prior to adding the antifreeze I drained the exhaust manifolds, the block and the water pump by removing the five plugs. I also add about 1 qt of antifreeze to each manifold via the thermostat housing. I disconnect and pour a quart of 100°f antifreeze into the inlet hose that comes from the sterndrive to protect the power steering cooler because there is no drain plug for it. The Merc user manual states the seawater cooling capacity is 15 qts. I used only 8 or 9 qts. I realize I didn't fill the manifolds. I've been winterizing this engine for eight years and I seem to recall that I used more antifreeze in the early years. Old age is setting in so memory isn't what it used to be, it may be failing me here.
