Granty

I have a slow coolant leak somewhere in the closed system of my Mercuiser 5.7 300 hp. 2008 with 200 hrs on it. I've checked all the hoses I can reach and the cap on the heat exchanger looks good. This is a sea core cooling system. Is there something I'm missing?

I have the open cooling system that draws in lake water. In that system are 6 blue plugs for drainage, particularly for winterization. I purchased this boat last Fall and noticed some leakage by evidence of rust stains just below a couple of the plugs. After replacement of all plugs, there were none leaking with the exception of the one plug at the "cool fuel" heat exchanger. And this plug is the most difficult to get a finger hold to tighten, but I had it plenty tight. After taking it out, I wrapped the threads with teflon tape, reinserted and retightened finger tight. No more leaking of coolant water. Since you are running a pressurize coolant system with antifreeze, its gonna be a lot different than my system. Put some newspaper under the engine, then start it for a minute, shut it off, then look for the leak onto the paper. Then repeat until you see where the drip is. You don't want to be crawling around a running engine.

Is the bilge bone dry?

Thanks for the input, I'll try the newspaper. The bilge is dry now after I hand pumped a large amount of anti freez.

If you have white smoke when you start the engine that disapears after a few minutes your manifold may need replacing. If you can smell anti freeze when you start the engine that is an indication of manifold or head gasket leak.