Quote Originally Posted by Fish Tales View Post
Check the impeller in the seawater pump.
I believe Fish Tales has almost certainly found your problem!

In case you have never had to change one before here is where they are located. If it is an Alpha 1 Generation 1 or 2 the seawater pump is in the lower unit! If it is a Bravo drive of any series 1, 2 or 3 the sea water pump is located on the bottom of the engine most often on the starboard side at the front! I have no experience with the OMC drives so cannot give any advise on them!