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1982 470 Mercruiser

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itsmiisally

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We have a 1982 470 Mercruiser. We are having problems with it over heating. We have replaced the Heat Exchanger from a 2 inch to a 4 inch. We replaced the Impeller (in the foot), the exhaust elbow and all the hoses. We also have replaced the thermostat 3 times. We are open to all ideas.
 
If it has been overheated the head gasket may have been comprimised. Perform a compression test on a warm engine. If the pressure is low in two side-by-side cylinders expect a blown gasket. You'll need to verify that the mating surfaces of the head and block are true using a straight edge. If they are not true both will need to be milled to true the surfaces...not cheap...engine will need to be pulled. If you have to go that route don't mess w/it and get a reman longblock if the boat is worth saving.
 
Seems to be a common culprit, even if all the blades are on the impeller you pulled I would still check the passageways and elbows in case.


kimcrwbr1 said:
Are you sure the engine coolant pump is circulating the coolant properly. check the temp of the engine coolant to and from the heat exchanger if the coolant going to the engine is not considerably cooler you may have blockage in the raw water system somewhere. With the over kill on the heat exchanger it would be either circulation pumps or restriction in flow.
Click to expand...
 
first you need to figure out what is wrong,

three basic overheat issues,

1. problem with water coming in, lack of water, air in the water stream, restricted flow due to a bad gasket or collasped rubber grommet or clog in water path etc.
2. problem with engine cirulation, engine pump, themostat or head gasket issue etc.
3. water going out, bad manifolds, elbows,
 
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