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petemac

Merc 5.7L overheating

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petemac

Could it be a thermostat? What is the best way to test the impeller function? It was only run 4 times on it. What should I look for?

The temp goes up to 200 then I shut her down. The heads were just replaced and I did notice a slight leak coming from one but that shdnt do it. Many thanks!!

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chadwick02

you should have a hose going into the impeller from the intake, and another hose going out of the impeller housing. You could disconnect the later hose and see if there is any water coming out of it when the boat is running. I would also check to see if the water hose filters and screens are clear of any debris. Not sure where they on your boat. Mine is right after my oil cooler.

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D-GOOSE

Did you have a over heating problem before replacing the impeller?

How old is this impeller?

Who replaced the heads?

Thermostat's are cheap and should have been replaced.

If the last impeller was bad then you need to remover all hose's to look for a block and also look on the inlet side of the pump as well.

If an impeller can form to a shape.

The wrong head gaskets could be a problem with some cooling hole's blocked.

If the eng starved for water at any point then the thermostat is shot. IMO

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JasonK

Check and make sure the hoses to the impeller housing aren't backwards. That will cause it to overheat, I found out.

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Sunsetter95

On your '95 Sunsetter, the trans cooler is on the left side of the engine and has a screen in the end that is feed from the raw water pump. Pull the hose, and as stated above, check/clean out any debris. Use a garden hose from the top to ensure you have good water flow. I also found that my main raw water intake hose was collapsing on the inside. It was ~50% blocked.

Are you in the lake or with a fake a lake? The fake a lake barely keeps the engine temp down at idle, so if you run at a higher RPM, it will get hot. Make sure the hose outlet is pointing at the front of the water pickup.

If you installed the impellar, double check the inlet and outlet hoses on the pump. It is easy to get them turned around.

The themostat is easy to replace. As long as the little plastic piece will come out. 160 degree is OEM. You will need to buy two gaskets.

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