Thanks for the feedback, antifreeze is antifreeze I don't think that it matters as long as it meets volvo specs. As to the porous block theory, it is not a porous block that I am having trouble with. The block is cracked 12 inches down the exhaust side of th water jacket. So far nobody has been able to tell me what the difference is between the 6304F block and the 6304S block. I can only notice by physical difference is there is two bolt holes not tapped but drilled. The knock sensors may be in a different locations from what I can tell. Any information is helpfull. Thanks for all your input. sped.