if you can take off a hose above the pump and fill it with water so the pump is primed and then go for a ride once it starts pumping the impeller can get seated in the housing a little better and will work better and better as it wears into the old housing 2 or 3 trips to get back to normal. Or if you can get on plane on one motor then start the other once you are moving the water pressure should prime it and get it going.

I had the same issue. I had to use the water pump rebuild kit. The scoring on the water pump allowed the old impeller to fit snug in the grooves and pull the appropriate water pressure. Once the new impeller was in, it would not follow the grooves so it was sucking to much air / no water. After rebuild kit was put in ran perfect.

What rebuild kit did you use? Any part numbers?

Contact your dealer , there is a recall on the Impeller

Have you backflushed your system?? You have old pieces of rubber in your oil cooler!

Search for the post Heads Up. Mercruiser finally came out with a service bulletin as to the issues. Your beating a dead horse. You most likely need the newest impeller in which might have green dot on it. Good Luck - the service bulletin is # 2013 - 06

Here you go: http://www.offshoreonly.com/forums/g...-heads-up.html

had a friend with twin 496.s same problem on both engines. ended up puting stainless steel shim repair kit in works 100% think it was about 50$ per kit don't remember where he ordered them from. google 496 sea pump repair kit several places make them. good luck.