It might be circjlator pump, But if it does it on the hose too Id say change raw water pump impellor. Change on both engines if you have time. You may have pulled some sand through and ruined it. You woulg know by looking at it. Good Luck, Mfb

Check the impeller, many times they will fail after sitting all winter.

Marc is most likely right, the tips on the rubber impellor will rip off and they will go to the cooler and give you a partial restriction, pull the seapump and remove the impellor and inspect it, the kit # you need is mercury 807151A14 good luck the kit is pretty easy to install you will need two kits for both motors and 454mag engines run around 170 to 175 degree's sounds a little hot but normal running temp

On the subject of temprature, what is the correct operating temp for a 454. Mine is a OMC King Cobra and the manual says 140 degrees but when I replaced the tstat for good measure, the new one is a 160 degree. I asked the guy where I bought it and he said 140 is too cold for a BBC. Now you got me thinkin. I do have a stock oil cooler if that matters.

Gents, thanks for all the helpful information. I did remove the sea water pump and on the port motor and inspected the impeller. You guys hit the nail on the head! That sucker was fried! I replaced the impeller and everything is okay. Now, I need another free afternoon to replace the other impeller.

Intolerant1, my t-stats are 160 degrees and both engines run 175 degrees at operating temperature. I believe Tinkerboater runs 140 t-stats in his big blocks as well as Troutly with his 500 EFI's.

I actually run 160 degree stats but the stock engines had 142 degree stats.