draining the block

When I went to winterize my boat (it has a merc 5.7 350) a few weeks ago, very little water drained out of one engine block drain, and the other side didn't drain anything. I ran about 15 gallons of antifreeze through it hooked directly to the water intake line. I then drained everything. When I opened up the plugs on the block, some antifreeze came out of the passenger side at a very slow rate, but none came out of the driver's side. I put a piece of wire up in the block, and that increased my flow a bit on the one side. Yesterday, I went back with a piece of sturdier wire and a small screw driver, and I was able to get one side completely open. I dumped antifreeze down the thermostat opening, and it came streaming out the plug opening like it's supposed to. Still nothing coming out the other side. I think part of the problem is the plug is on a fitting underneath a knock sensor. Thus, it's hard to get the hanger in there as far. If I pull the knock sensor, will water drain from there?

Also, how is the cooling system settup? I know water goes in from the top after going through the thermostat. Other than right there, is there any place where both sides of the block are connected?

The sides are separate. The connection is the intake manifold. You can drain through the knock sensor. If no liquid can be passed through, you have problems - mechanic time.

Then block and heads are made from sand castings. Sand, and sometimes rust can drop to the bottom of the block as water circulates. Sometimes it's hard water deposits too. Draining the block or flushing it gets rid of most of that. Using a wire like you did will help clear it. If you can't clear it you could have a problem.
A reverse flush system like you can get for a car can also help clear it.

If it was completely stopped up, wouldn't the engine overheat? Just a thought.

"If it was completely stopped up, wouldn't the engine overheat?"

Yes, if one side were completely blocked, that side would overheat... but not necessarily in a way that will show on your thermostat. Keep in mind that the thermostat is only measuring temperature in one place on the block. Pull the knock sensor and see if that helps drainage. You need to find if the water can't escape or if there's no water on that side to begin with. the latter is a more serious issue but at least it's one you have all winter to figure out.

I don't think it would affect the engine temp at all if the drain plug was clogged. That is only there to drain water in the winter.

PLEASE don't use automobile antifreeze. Those products are not safe for our water ways. Use only a Marine/RV antifreeze like this:

http://www.peakantifreeze.com/rvmarine.htm

It was rv antifreeze. I also hope to have the clog figured out soon. As such, I drain the block before putting it in the water anyways.

I got the clog out. Now I just hope I wasn't too late as we had a 20 degree night a while back

You should be ok, it takes a couple of days below freezing to freeze all that water to a point where it will crack the block...

Do you guys put a light bulb in the bilge on really cold nights?

What wattage of bulb?

I've heard from a dealer that a 45 watt bulb in the engine compartment should keep the block from freezing...Granted we are in NE Tn and not sub freezing temps but take it with a grain of salt. I didn't winterize last year, We store mine in a sealed barn, Lamp in the engine compartment (35 watt) sleeping bag over the back vents, plug in on the bottom and foot down and a flood light on it...if temps got extremely low we had a kerosene heater to run intermittently. Never had to use it...You should be good with what you did, but for added protection I dont think a little lamp would hurt...Mine is winterized this year and im still putting in a lamp just for my peace of mind lol

If the bulb (chinese made extra good) happens to pop it can ignite your boat. There can be fumes in there esp. if you have the vents covered up. I'm not saying I haven't done it in a pinch but I'll take the time to drain the block and manifolds. A light bulb won't protect your heater or shower if you have 'em. I've also had pumps go bad because the ballast had a little bit of water in the system.

well very true...that was always my fear about the fumes building up..then I said eh...I have insurance on the boat...so if It goes up, it goes up lol...lots of love for my boat cant you tell..