Re: Mercury 650 cooling problems.
Ok, on that engine there is a thermostat and popit valve, they control engine tempiture but have nothing to do with the telltale flow. On that engine the water is pumped up the tube to a chamber that supplies the engine with cooling water through the thermostat and popit bypass and has a hose that come out of the spacer plate that supplies water to the water cooled fuel pump which dumps it over board through the tell tall. Start by pulling the hose off the spacer elbow and start to check flow, there will probably not be any because the plastic elbow that the hose came off of is usually plugged or melted inside remove it and restart if there is water the elbow was the problem if no water take a piece of hard wire and put it in the hole and try to rod it out with the engine at high idle, if that don't work the power head will need to be removed as the adapter plate is plugged or there is a blown gasket. If there is water at the elbow with the hose removed then either the fuel pump is plugged or the 2 hoses. All of this of course is counting on a good pump from the w/pump and remember just blowing air through it proves nothing, it takes water to flush it.
