Haven't posted here in years. I need to that more often. I have a problem with a 1967 Mercruiser 160. I suspect water is getting into the engine via the Exhaust Manifold or head gasket. My oil is very milky and the engine runs bad. It idles awful and doesn't like idle while in gear. It will shut down. In fact it wont idle below 1100 rpm. That's not idling is it. Today I removed the exhaust/intake manifold and found droplets of water in the most forward, and most rearward exhaust ports. So I did a test and hooked a garden hose to the water inlet to the manifold to see If water would come out the elbow. What I got was this. Do I need a new manifold?
Figured it out. Baffle separating the exhaust from the cooling water jacket rusted through. Need a new aluminum exhaust manifold. If you have one and want to part with it let me know! Its Mercruiser part number 35155