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Hello,


I have recently had trouble with my 1985 200hp Merc Black Max. It seems like it is overheating. It idles just fine for as long as you need, but once you get up to speed, it will accelerate to running RPM, then within a minute or so, it will hesitate then drop itself back to idle. It seems to be much hotter than normal. After it does this and i kill the engine to look at it, it wont start back up.


I figured it might be a bad impeller in the water pump, took the lower unit off, perfect. So i figured there might be something in the cooling lines, pulled all the rubber hosing off, though it needed to be replaced, it was still just fine. Next i went into the cylinder head cover for the thermostats, they were virtually non-existant, corroded to the point of not being there. Could that be the problem there?


Next i pulled the water pressure regulator (i think thats what it is called, on the starboard side of the engine, just above the powerhead mounting bolts), there was a ton of corrosion and buildup in there, but i dont think there was any blockage. After that i pulled the cylinder heads off, lots of buildup, but no blockage that i can see. Pistons and cylinders are clean and undamaged. Pulled the exhaust manifold covers off as well, nothing seems to be crazy in there either.


If anyone has any suggestions as to what else to look for, and/or what to look for in the parts that i have already pulled, it would be greatly appreciated.


Thanks,
Dan
 

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Dan,

Any corrosion or build up will limit the flow of cooling water and the ability of the metal to pass the heat on to the cooling water.
 
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