If it’s overheating and you have a closed cooling system, it’s probably leaking coolant out of the water pump seal. I had to sleeve the front end of the cam shaft (it’s integral with the water pump and not real easy to access). You need to pull the harmonic balancer, which houses the alternator (though by now you may already have an aftermarket external alternator installed).
I think it’s a good engine if it’s in good shape but if you have to bore it out, buy a bunch of parts, probably including all new rubber on both sides of the transom, this is exactly the time to consider bracket and outboard.
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 Scott, Portland, OR '85 V-20 I/O, Merc 170
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