Somebody else had a problem like this and it ended up being the head gaskets. Something about core shift in the block left a very small sealing surface between the mark IV heads and the Gen 6 block even with the proper gasket.

I also have heard of issues of the gen IV head on a gen VI block even with the "correct gaskets"

first time on stand no water in 40 minutes. second time water in 15 minutes. what did you do differently?

my guess is the water pressure on the stand vs in the water is quite a bit different.

on the run stand it had app 12 lbs,in the boat i saw 23 lbs,that is not excessive pressure.i put 35 lbs of air pressure and cannot detect a leak.tomorrow im going to get some dye and put it in the radiator on the run stand,then im going to run it to 180 deg,then im going to pull the intake&heads and see what i find,then im going to jump off a tall bridge.well maybe il skip the bridge jump.

nothing,i just put it in the boat and went for a test ride.

Chit happens to the best of em bro . I am impressed that you did not let pride get in the way of asking your brothers for ideas . Speaks volumes about you .

when the engine first came to me it had this problem but it had a cracked gm iorn head,that is why the edelbrock marine heads were purchased,i wish i had a set of gm gen6 heads to throw on it and see if it still leaks.

thanks,i know there are a lot of smart guys on oso and i am always willing to listen to ideas,i guarentee you i will figure this out as it has now become a challange to me.

just want to mention the dye idea came from FIXX .