I have been debating about sucking in antifreeze with the engine running or just pulling off the hoses at the thermostat housing and filling them with antifreeze. The latter is the way that I did my previous boat and it worked well. It had a GM vortec V6 with an outdrive. After I completely drained the block of water. I would take off the large hose at the thermostat housing and pour in antifreeze until it ran out the outdrive exhaust. It would take about 2 gallons, so you know it was filling up the block. Then I would remove the two smaller hoses and do the same thing. These would take about a 1/2 gallon before coming out of the exhaust. This was how a professional marine service guy taught me how to do it.
I haven't looked that closely at the MCX 350 engine yet, but shouldn't that same procedure work to fill the block on it?
My only worry is that if I run it up to temperature with water and then drain the block, that the engine would cool down enough to close the thermostat.
Last edited by blackhawk; 10-08-2013 at 06:05 PM.
Reason: forgot something