Closed cooling system drain Mercruiser 5.7

[RAW BAR]

I haven't been able to find where to drain the coolant out for a drain and fresh refill. Lots of info out there on the seawater side, but not much on the closed coolant side. Mercruiser 5.7 MAG Horizon inboard.

 

[Jimmy Buoy]

Each engine setup is different, but I would assume that you'd remove the Blue Tube attached to "H" (engine circulation pump) and drain. Next would be to remove both the starboard and port side engine block drain pugs (they're low and center on the block just above the oil pan). To be thorough, the hoses feeding the bottom of each exhaust manifold AND the hoses coming from the exhaust risers (the lower of the two - blue on your diagram) should be drained. Reattach all hoses.

To refill, not sure - haven't done mine yet. I'd start by filling the expansion tank, start the engine (with cooling water flow) and see if the AF gets drawn in naturally. If it doesn't, before the engine gets too hot you might have to stop and remove the big hose from your circulation pump again and replace it with a length of the same hose so you can pour in AF until AF starts to come back out of the heat exchanger hose that normally goes to the same circulation pump that you're feeding. Reattach the heat exchanger hose and try getting the system to draw AF from the expansion tank again. Burping the system usually is done via the expansion tank since it is the highest point in the cooling system. Just keep filling the tank as it gets drawn into the system.

Good luck - hope this helps.