1984 470 mercrusier Running hot


Old 09-21-19, 06:36 PM
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1984 470 mercrusier Running hot

Have checked all fresh water pump , heat exchanger, check water flo through heat exchanger is good, still engine block and antifreeze resevour still getting hot. Hot enough to almost set engine cover on fire and burn up ignition coil. How do i check it antfreeze circulating. What else should I check.
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Old 09-22-19, 05:40 AM
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First are you sure the boat has fresh water cooling? Many of them had raw water cooling but they don't have heat exchangers.

Next I'd make sure the engine coolant pump is working. You can crack a hose loose and see if coolant sprays out when the engine is running. Or, you can pull the coolant pump and make sure the impeller is good. More commonly I have trouble with the raw water side. Make sure you are getting water flow through the entire system. Intakes or the raw water strainer get clogged, or the raw water impeller needs to be replaced.

Where was the boat used? Anywhere barnacles or zebra muscles are present? If so then I'd visually inspect the inside of the heat exchanger. Just because water is flowing through it doesn't mean the interior isn't covered in critters that are impeding the transfer of heat.

Also check the thermostat. For a quick check you can just remove it and see if the engine cools. For a better test you can hang the thermostat by a string in a pot of water while you heat it on the stove. Check the water temp with a thermometer and see if the thermostat is opening at the correct temperature or at all.

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