K. - Am going to try this communication thing again. There is a (1)seawater import - that goes to a (1) seawater pump. Am I wrong in assuming that if one (riser) side is cooling properly than the single pump that supplies both is ok? I have pulled all 3 hoses off the riser - no apparent obstructions. There are 2 drain petcocks below the riser. The 1st, nearest the front of riser has solid flow. The 2nd, more towards rear is so-so. I see there is also a (1)circulating pump @ front of engine but again, if one side is cool than this is also functioning ok? Am just trying to avoid what looks to be a large? job pulling the cast riser and then - how to clean? Also would have to replace gaskets, etc... I'm NO mechanic and no one seems to want to come out to Marina to service (outside of their drive in shops).
Hi, unfortunately the most likely place for an obstruction is inside the cast riser.
There are openings in the riser that spray hot cooling water into the exhaust flow, this is what keeps the exhaust boots from burning out.
Cast manifolds and risers rust inside the water passages and eventually flakes break loose and can clog the outlet holes.
No doubt about it, it's a big job but not huge. You will need new gaskets and the gasket surfaces will need to be clean and true. They will need to be sanded with a hard flat sanding block if you expect them to seal well.
Loose rust can be shaken out or flushed with water. You can loosen scale a long thin screwdriver.
Clean it out as best you can, sand the gasket surfaces flat and reassemble using new gaskets.
Drain cocks tend to get an accumulation of crud built up just inside of where they screw in, if it drains slow, remove it and clear out behind it with a screwdriver or other prod.
Ok. Will try to remove and look for blockages in riser...
24 yrs exp. Inboard/Outboard mechanic Mercury/ Mercruiser, Volvo Penta and OMC, Johnson/Evin.
If it's full of rust crud, you found the problem.
Let me know what you find.