mercruiser circulating pump
 

I have a 454 mpi that eats circulating pumps. The first one went at 13 hours,mercruiser ate that one .Dealer said mercruiser had a bad batch.Now engine has 45 hours and leaking again.What is up with these pumps.Had a 350 mag for 7 years never had a pump go bad. They must have gold inside for the price.

My guess is you have the same problem I had. Excessive water pressure. Do you have the thermostat housing with a total of four hoses? I way to confirm the pressure is high without a pressure gauge is to make a blast with the engine hatch propped up so you can see the large hose going to the circulating pump. If it looks like its going to burst when running WOT then that's the problem. Anything over 24lbs. eats circulating pumps and many engine builders say hurts intake runner and head gaskets. You may want to put a gauge on the engine to see what the pressure is at. I am currently filling a complaint with Boat US against Merc about this problem.

Dan