What is the downside to adding antifreeze through the drain plug openings instead of pouring it down the thermostat housing? Don't laugh....

The last time the engines were out, I fabricated 4' drain lines for all the block and cooler drain holes, much like an oil drain hose. Makes draining the water out of the block very easy. As my boat uses transom-mounted pickups, and does not have sea-strainers, sucking antifreeze through the engine while running is not possible. Will putting a few gallons of antifreeze in through the drain hoses be okay, or do I need to pull the thermostat and fight with trying to get it to seal again afterwards?

Is it possible to disconnect the hose from the transom mounted pick up and suck it up there? I use to first drain the block and then disconnect the inlet hose from the transom assembly and put it into a bucket of anti freeze and then run the engine.

Pulling the hoses off at the transom pickups and puting them in a bucket is a good idea, but it's not very possible in my boat.

If you can hold the drain hose up above the block, and it takes ~ 3 gallons of antifreeze then you have it filled. You are going in from the bottom, so I'm not sure it will work, but it should like it does when you fill the outdrive.

If it doesn't work, you don't need to pulll the thermostat housing to fill the block. Just pull the big hose that goes to your circulating water pump (or crossover if thats what you have). Fill that big hose till antifreeze comes out the thermostat hosuing where you pulled it off from. Then the block is fill.