Hey guys, I think I have a bad circulating pump but I wanted to get some outside opinions before I order a part.
Engine: 1999 Mercruiser 7.4/454 MPI (not magnum) with raw water cooling (serial number 0L347xxx) with Bravo 3 outdrive. Actually it's dual engine but only having the problem on port engine.
What I've tried: Rebuilt the raw water pump (it was needed anyway after it it destroyed an impeller last year due to a crack inside)
Symptoms: Engine gradually reaches high temperature while idling, somewhere around 200F (and yes, it's actually overheating, the thermostat housing was HOT!). There is some cooling happening, but it's clearly not where it should be. One of my other fears is that part of the impeller that disintegrated last year is still in the loop somewhere causing a partial blockage, but I had the boat out twice after replacing the impeller (but prior to the full rebuild). The impeller I replaced today didn't have any pieces missing. Also, I took the large hose off the thermostat housing and poured water into it and hot water flowed out of the top of the manifold from the engine. I did this both to check for restrictions and to cool my engine down. Lastly, the weep hole on the circulating pump appears to have serious corrosion, probably from water, but it was dry when I inspected it. The same hole on the starboard engine shows no signs of corrosion.
Thanks for the sanity check, I'm fairly sure I correctly identified the problem, but I'm not a mechanic so I wanted to be sure before I ordered parts.
Dan
Engine: 1999 Mercruiser 7.4/454 MPI (not magnum) with raw water cooling (serial number 0L347xxx) with Bravo 3 outdrive. Actually it's dual engine but only having the problem on port engine.
What I've tried: Rebuilt the raw water pump (it was needed anyway after it it destroyed an impeller last year due to a crack inside)
Symptoms: Engine gradually reaches high temperature while idling, somewhere around 200F (and yes, it's actually overheating, the thermostat housing was HOT!). There is some cooling happening, but it's clearly not where it should be. One of my other fears is that part of the impeller that disintegrated last year is still in the loop somewhere causing a partial blockage, but I had the boat out twice after replacing the impeller (but prior to the full rebuild). The impeller I replaced today didn't have any pieces missing. Also, I took the large hose off the thermostat housing and poured water into it and hot water flowed out of the top of the manifold from the engine. I did this both to check for restrictions and to cool my engine down. Lastly, the weep hole on the circulating pump appears to have serious corrosion, probably from water, but it was dry when I inspected it. The same hole on the starboard engine shows no signs of corrosion.
Thanks for the sanity check, I'm fairly sure I correctly identified the problem, but I'm not a mechanic so I wanted to be sure before I ordered parts.
Dan