Milky foam shooting out of top of motor, but none in oil pan

Ok I have a 1989 MerCruiser 2.5L motor..

I took the boat out last summer and after about 10 minutes of running a milky white foam started shooting out of the top of the motor (I had the flame arrester off as I was adjusting the carb which always runs rough unless I manually hold the choke 3/4 closed, but save that for a different post)

SO I figured either the block was cracked or head gasket went..I was surprised to find zero water in the oil pan and oil was clean as a whistle. I didnt take the boat out again and when I went to winterize it, i found winterizing anti-freeze still in the motor AFTER I had it in the water earlier in the year...I wonder if the thermostat is bad and the antifreeze never got flushed out, and if this has anything to do with the stuff spewing out of the top after 10 minutes of running.

any idea what I should be looking at first before I start ordering parts?

Re: Milky foam shooting out of top of motor, but none in oil pan

You have a cracked block.

This thread should explain it http://forums.iboats.com/showthread.php?t=369864

I would bet the oil is clean in the dipstick tube, not the rest of the pan.

Re: Milky foam shooting out of top of motor, but none in oil pan

wow, you're good and dead on...the oil and water had separated, dipstick was clean, but oil drained started out clear but got milky.

but here's the kicker here, i flushed everything out and put fresh oil and fliter in. when flushing antifreeze out I pulled the thremostat and it was seized up. I was surprised to see that the block was full of a completely different colored antifreeze that I used. I took the boat out about a dozen times the first year, winterized it per the service manual, flushed it and it was the 4th time out that the "foam" was shooting out....so the old antifreeze simply sat in the block the entire time I owned it, prob due to the thermostat....I'm not sure how the block could crack full of antifreeze, but IF the thermostat was not allowing any water through and it was simply coming in and right back out through the manifold, could the overheating have blown the head gasket not cracked the block as what happens 99% of the time?