I have a 2005 496 MAG HO with black murky water in the closed cooling system and need to flush it. But where do i drain the system? Anyone got some pictures or drawings of the drain plugs?

I got no oil or bad odor in the water, and no water in the engine oil, so i dont suspect there is anything wrong other than old antifreeze.

Ayuh,..... The block drains are one on each side, down low, just above the oil pan, port side is just ahead of the oil filter boss, 'n the other just ahead of the starter,....

Block Drains 496 Circled

Thanks, now at least I know what I’m looking for.

And please make sure you use plumber's tape or the goo on them when you reinstall. I've had friends skip that and it made things difficult for them.

You could have a leaking heat exchanger, so the coolant has been slowly diluting with sea water.

The "pink" coolant is only good for 7 seasons, maximum. After that it starts to turn dark/metallic, and silts up, and doesn't flow/cool as well.

On a twin engine boat, sometimes it is REALLY hard to get to those drain plugs. Do the best you can to get it all out. If you can't get to both of them, you can flush with good clean water to get a majority of it out.

I got single engine, but still pretty tight. I think I’ve located one of the bolts so I’ll start there.

Yeah, rinse out the expansion tank too. It will be filled with black metallic sediment.