So I have a 1988 mercury 2.4l 200 I blew up. I put a 1996 2.5 pro max powerhead in its place on top of the 88 midsection. Runs great but I can’t keep it cool nor get any water pressure on plane. 1-3 lb at idol 3-5 at wot. Motor is in water good while on plane . tell tell always got water coming...