Need advise on merc 350 260 please

I have mercruiser 350 260 that has water in the oil and was hydrolocked. I pulled the plugs and had some water on top of the cylinders .. I also check the compression due to lacking power and found no compression on one cylinder. I pulled the valve covers and had a stuck valve and obvious evidence of water. When I took the exhaust manifolds off it did look like one of the gaskets may have been leaking. There isn't a lot of rust but this is a new problem but the number 1 Cylinder exhaust manifold port looked like there was a water trail. So now I have the intake off and just removed all of the bolts from the heads. I didn't take the heads off because I didn't have time but all I have to do I pull them off. I'm going to check the head gasket obviously but how can I check to see if the block is good? The valley looks good there are no cracks but I don't want to put this back together if the block is toast. I'm going to put vortec heads and intake on when it goes back together. But how can I make sure the block is ok? Thanks for the help!

Re: Need advise on merc 350 260 please

How much water? Is the level high on the dipstick? Is it real milky and thick?

Re: Need advise on merc 350 260 please

Leave the heads on & pressure test! Would have been better w/intake inplace.

Re: Need advise on merc 350 260 please

It was pretty milky. Changed the oil and took 2 gallons out of the crankcase

Re: Need advise on merc 350 260 please

After I changed the oil I started it and let it idle for probably 15 min and checked the oil and it looked good. I then drove the marina, 1/4 mile, to take it out of the water and the oil level was right back up again, about 2 gallons.

Re: Need advise on merc 350 260 please

You have a cracked block.

Re: Need advise on merc 350 260 please

Ok, so how can I check to see if it it cracked?

Re: Need advise on merc 350 260 please

Amitchell001 said:

Ok, so how can I check to see if it it cracked?

Click to expand...

Refer to posting #3. If you need a DIY explanation try the 'search' in this forum.

Re: Need advise on merc 350 260 please

I understand that if the motor was together I can pressure test the water jacket. What I am asking is if there is a way to tell now. I took the heads off and the cylinders look good. There are no cracks. The intake gasket was pretty bad though. I'm actually thinking the intake gasket was responsible. I did have a problem with the boat not reaching full rpms and being underpowered. When I took the heads off one valve was stuck and cracked and another appears to have been stuck and not firing for a while because of the buildup on it. I have always winterized my own boat and I did winterize it last this last winter as well.