I have a 1982 Mercruiser 470. Since I got it a couple of years ago it has been overheating at high revs. (over 200 degrees F.). I know this engine has a history of problems, but this one has had most of them fixed already- new alternator, new 4" heat exchanger, etc. I replaced the cam seals 2 years ago. That's the only problem I've had other than the overheating.
I have removed the risers and heat exchanger and cleaned them out (they weren't that bad). I replaced them with new gaskets, etc.
I replaced the water pump and impeller. I also removed the water-cooled voltage regulator (not needed w/ new alternator). At that time I tested the water flow rate from the pump and it met specs. I have drained and flushed closed coolant system a number of times. There seems to be no air bubbles in the coolant.
At that point everything led me to believe a head gasket leak. I sent the boat off to a trusted mechanic. He did all the things I did a second time. In addition he installed new plugs and wires. He also pressure tested the cylinders and said they all held pressure (150 psi for a few hours I think). That ruled out the head gasket.
I thought the carb could be running to lean but he said that wasn't possible with this model. We're now leaning towards some internal deposits that are hindering the temp transfer. He's afraid to do an acid wash because of the tin and copper (or brass?) parts that would be damaged.
Now he says the only real option is to start taking the engine apart to see what we find. However, that could get expensive, and parts may not be available.
So...... before I sink this, I mean sell this boat (with disclosure of course) I thought I would see if anyone here has any last suggestions? You guys are awesome and I really appreciate your help.
I have removed the risers and heat exchanger and cleaned them out (they weren't that bad). I replaced them with new gaskets, etc.
I replaced the water pump and impeller. I also removed the water-cooled voltage regulator (not needed w/ new alternator). At that time I tested the water flow rate from the pump and it met specs. I have drained and flushed closed coolant system a number of times. There seems to be no air bubbles in the coolant.
At that point everything led me to believe a head gasket leak. I sent the boat off to a trusted mechanic. He did all the things I did a second time. In addition he installed new plugs and wires. He also pressure tested the cylinders and said they all held pressure (150 psi for a few hours I think). That ruled out the head gasket.
I thought the carb could be running to lean but he said that wasn't possible with this model. We're now leaning towards some internal deposits that are hindering the temp transfer. He's afraid to do an acid wash because of the tin and copper (or brass?) parts that would be damaged.
Now he says the only real option is to start taking the engine apart to see what we find. However, that could get expensive, and parts may not be available.
So...... before I sink this, I mean sell this boat (with disclosure of course) I thought I would see if anyone here has any last suggestions? You guys are awesome and I really appreciate your help.
