cracked head ? Block or head gasket?

[NCali]

87 1/2 ton with a 305 tbi

truck runs fine until the thermostat opens, then it billows out clouds of white steam out of the tail pipe. Shut it off at that point and when I try to restart it there is enough water in what ever cylinder that it wont turn over , it just locks up, . 10 minutes later it will start again
my question:  cracked head, block or head gasket

[Blazin]

Pull it apart the only way to tell.

[80Chevy4x4]

definitely have to pull it apart to find out...when you pull your spark plugs look for the one that shows water on it...then when you pull the heads off you know which cylinder to really look at...i just had to replace the heads on my 350....one was cracked between the intake valve and the water jacket.

[NCali]

so it is not apart yet but I have the exhaust off of 1 side and#4 and #6 are wet

[SkinnyG]

Post pictures of your head gaskets too.  That may help.  Look especially close for cracks between the valves and/or into a spark plug hole.

Mine were blown (see the dark patches):

[Rattler12]

Most likely a head gasket if 4 and 6 are wet......

[NCali]

Long crack between the water jacket and exhaust valve on #6 on the face of the head next to the egr port