Thank you for the question XXXXXXXXX,

The lower bellows is (About 3 inches in diameter opposed to the U-joint bellows higher up and 6 inches around) is used for exhaust to exit the engine and be directed through the rive and out the propeller. Running the engine with a rip in "these" bellows will cause no harm. We do need to change the bellows at a early convienion. If the bellows rip loose and get jammed into the u-joint bellows while trimming down, this could cause the u-joint bellows to contact the u-joints and this will surely rip the u-joint bellows. If the u-joint bellows has a rip, this will need to be repaired without further use (Needs to stay dry in the u-joint bellows).

There is likely no "petcock" to drain this engine block. But there is a plug just in front of the starter on the starboard side of the engine, of course on the engine block.

The thermostat when closed will allow some passage of fluid, but likely not enough to sufficiently "Load" the water with antifreeze. The only sure way to know if the antifreeze made it into the block sufficiently is to take a sample out of the block and test it with a anti-freeze hydrometer. (These are available at all the auto parts stores).

I just pulled the parts diagram from Mercruiser for this engine and, for the life of me, cannot locate the rain plug to give you a diagram of it's location....I have not seen one without this drain plug or petcock. ..You have a LX model, so we need to look for a knock sensor in the location I indicated above or on the other side of the block tucked under the manifold. It will look like a large oil pressure sender, and this is screwed in the drain port. ( I believe there is a drain plug, we need to keep looking. )

No, not hardly....The thermostat under full power conditions is only "burping", new water into the engine block every few seconds. The water circulating pump is, well, circulating the water through the block and recycling the the same water. Other water is being directed to the exhaust manifold and to the exhaust gases all the time. When the engine gets to operating temperature, the thermostat opens, allowing water to exchange in the block, just a few seconds later the water in the block is cooled by this influx of new water and the thermostat closes. This keeps repeating with the thermostat opening and closing every few seconds when at high power settings. Much slower at a idle or low power settings.

I would believe that the anti-freeze is likely very week in the block, given the application indicated above.

Another expert added this while I was away (drain plug is a 1/8 pipe plug screwed into 1/4 adapter on the port side rear)...

One of two ways is acceptable at our shop;

First choice is to run the engine is anti-freeze solution for 15 minutes....This will require a large bath of solution to run the engine that long.

Second is to drain the engine first and then do as you indicated before. The block will fill quickly and all will be fine.

Its just the block being full to start that is giving us the issue, and the time it would take to achieve the 50% mix in the block area without taking any chances.

There is definitely a drain, we do need to find it.

Wanted to add:

We can drain the block by removing the large water hose between the thermostat housing and the water circulating pump. Remove it on the circulating pump connection and all the water in the block will drain out........