Just found out that my third set of heads have cracked. '99 5.7 EFI with about 165 hrs. on it (bought new in '01-so this is the fourth boating season). I've had the OBC checked, and no recorded spikes, nor did the alarm go off. The impeller has been repaced each spring, and new t-stat installed. The prior work has been done by two different shops, each with Mercruiser "certified" techs. I really feel that there is a problem with the base engine. so the question now is---does anyone know if Mercruiser will replace an engine? Thanks in advance-Larry 