First off the engine is a 2004 496 HO with a Raylar HO 600 kit installed. After a hard run the other evening the temp climbed and alarm went off open hatch to see coolant everywhere in the bilge and tank empty. I poured lake water into reservoir to lower temp and to limp in and it worked. The next day I have had no luck locating where the leak is coming from, I dump water into the reservoir and it drains about as quickly as it
goes in.

http://www.boats.net/parts/search/Me...TEM/parts.html

I've attached the schematic of the heat exchanger and "it looks or feels" like the leak may be coming from the bottom end of hose "29".....where does this connect to? Is there any other known problems I should look for?? All the coolant is going into the bilge, oil is fine. I briefly tried to take this hose off but was unsuccessful due to lack of tools with me.

Grommets "14" are known for drying out and weeping.

You are now going to do a full coolant flush. I'd recommend a few new hoses, all new hose clamps, and those new grommets. With the additional RPMs of the Raylar kit, you are creating slightly more pressure with the circulating pump; which could be part of your issue. It could also be the circulation pump itself. They don't last forever.

I'd also have your heat exchanger thoroughly pressure tested. A leak in such can and will cause coolant to "expand" (mix with sea/lake water) and over-pressurize your 'closed' system.

I will take as much of the system off today...how hard is replacing the pump and how do you really know it is bad?? I assume the bottom side of hose "29" attaches to the pump...I really cant see into that space so its hard to really pin point where it is dripping from but something is definitely dripping from that general vicinity.

After further investigation the water is definitely coming from the circulating pump...it is flowing from the front seal. So now the next question...how hard is it to replace?

Spend some time on www.mercruiserparts.com looking at the schematics for the front of your engine via the parts breakdowns. There are also service manuals available for the engine from Mercury.

Depending on how much room you have between the front of your engine and the bulkhead; it may be a futile task best tackled by pulling the engine. Or, depending on how your boat is laid out, see how much of the rear seat you can remove.

So I have fixed the problem...I replaced the water circulation pump just because I had it but after disassembly I noticed clamp 31 was broke and gasket 4 (see schematic in post 1) was in poor shape....this had the be the original issue. I am still unsure what would cause the hose clamp failure...age? increased RPM causing increased pressure?? Either way it was an easy fix about 5 hours of my time and $500 in parts including the pump and fresh anti freeze.

I have 415 hrs on my 496 and was thinking about pulling the motor in the off season to clean and paint the bilge. WHile it is out I may just change the pump to avoid future failure....