'71 Johnson 6hp overheating

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skebo

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New to the forum. Thanks in advance for the help. Purchased 1971 Johnson 6hp. Was pumping no water out the exhaust port, so put in a new water pump and pumps water like crazy. But ran for a bit and then froze... way overheated. Loosened the cover off the thermostat housing and when it cooled down, ran it again and water seeped from the gasket, so is getting water to there. But there is no thermostat in that housing. Does there need to be? And any ideas why with water pumping so well it is still overheating? Hopefully didn't mess up the heads with the overheat. Thanks
 
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Daviet

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Re: '71 Johnson 6hp overheating

With no thermostat the water should flow freely, remove the thermostat cover and pour water into the housing, does it run right through or just fill up the housing. Maybe there is a restriction somewhere.
 
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skebo

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Re: '71 Johnson 6hp overheating

I'll try that but I blew air into the thermostat ports and got bubbles from the exhaust ports. But I don't know the path the water takes, so don't know if it is moving through the head. Stumped....
 
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skebo

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Re: '71 Johnson 6hp overheating

Also am really wanting to know if you think I trashed the motor overheating it like that. Right after I replaced the pump impeller it all looked good. Good stream of water at the exhaust ports where there was none before the impeller change. So was running it in test tank, rev up, rev down and so forth, checking gear shifting, for two or thee minutes, then started bogging down and stopped, pistons froze. After it cooled they turned again, but how will I know if its trashed or not. Am going to repull lower end and check water tube and grommets. Should I pull head and check that too?
 
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skebo

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Re: '71 Johnson 6hp overheating

By the way, I poured water into the thermostat housing (all holes) and it drained down and out the exhaust ports in housing and lower end.
 
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AlTn

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Re: '71 Johnson 6hp overheating

pulling the head and inspecting the pistons, rings, cylinder walls would be a good idea...new head gasket and surfacing the head before installing it will be required...further damage may require more
 
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Cap'n Chaos

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Re: '71 Johnson 6hp overheating

If it is running too lean it will cause it to overheat quickly as well.
 
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skebo

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Re: '71 Johnson 6hp overheating

Ok. Swallowing pride here. Went back and retraced my steps on the impeller replacement and (you stupid idiot!) missed the water tube with the pump housing grommet. So hopefully my screw up will be a help to others. There's not much room in there when you're putting all this back together so peek up in there and be sure the tube goes in the hole. Runs smooth now. Can keep my fingers on the heads at idle without getting too hot. At hi speeds it a bit too hot to touch for long. Does that sound about right? Hopefully won't have to pull the heads. Thanks all.
 
kfa4303

kfa4303

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Re: '71 Johnson 6hp overheating

That sounds right skebo. I think you got her fixed. No worries. That's a very common problem. It's always the little things. Run her at idle in a tank qith plenty of water for 10-15 min just to make sure she's good to go. congrats.
 
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