Re: 850 mercury 1975 thermostat?
My 1979 70 has 1 tube going to the TT and 1 tube going to the exhast base plate. The water coming out of the back 2 holes of the midsection (Rear exhaust midsection port) are cool and the water coming out of the TT is more than warm. Because it takes time to fill the exhaust port and water jacket, it heats up, and maintains that temp through the TT. If it,s hotter than it should be there "may be water" seeping by the exhaust baffel gasket or corroded baffel, and into the the internal exhaust port which in turn lets exhaust gases into the water in the water jacket superheating the circulating water which would also mean you would have water intrusion into your engne block by suction of the piston ( Usually the lowest one). Not good. I took mine off and as a result did a total tear down of the engine revealing 1 damaged piston 1 ground Crankshaft journal a set of needle bearings that where half there normal size, as well as wrist pins and the bearings there even worse.There is NO thermostat on my engine, None! and no place for one I can see. I would get gaskets and inspect the exhaust port, and exhaust baffle plate then check the piston walls for corrosion through the prots, and if ok I would replace it with new gaskets then re torque and re check the water tempature. If there is no water coming out of the exhaust midsection port check the upper out let of the water jacket (To TT) also check the water tube coming from the Fuel pump this one goes to the exhaust baseplate and then to exhaust midsection port. Disconnect the hose and see if there is water flow. If not you may have a totally blocked section in the motor or fuel pump water tube is clogged. I would not rule out the exhuast block base plate gasket for corrosion buildup or leaking gasket. Anyone owning an older engine should check this and for the price of a couple of gaskets save there engine, Take about 1 hour to do
