1967 6hp Johnson Overheating

Hi all! i recently purchased a 1967 6hp Johnson for a small jonboat. The motor overheated the first time out and I shut it down quickly. Noticed no water coming out exhaust ( ne pee hole). I pulled LU and found impeller seperation so i replaced entire water pump. No she pumps out the exhaust hole at all times but still overheats after 2-3minutes at WOT. Idles ok for quite a while. Once the motor colls its starts right back up. Any help would be appreciated.

Thanks

Re: 1967 6hp Johnson Overheating

i believe that has a thermostat, change it, especially if it was run
in salt water, a lean fuel mixture can also cause overheating
also could be a defective water pump, even though new

Re: 1967 6hp Johnson Overheating

yes it does have a thermostat, under a triangular plate on the top of the cylinder head.

Re: 1967 6hp Johnson Overheating

Thanks guys! I looked under the trianglalur part ( 3 screws to remove ?) and there is nothing under the cover. Just the water passage. I ran the motor with the cover off and water comes out. But then again it also comes out the exhaust. I thought as long as it comes out the exhaust then it was making through the block. Also, just for my own education, if there is no thermostat shouldn't it be colling ALL the time?

Re: 1967 6hp Johnson Overheating

You might do a compression check may have a bad head gasket.

Re: 1967 6hp Johnson Overheating

If the Impeller came apart there is a good chance that there are bits of it blocking the waterways. Pull the lower unit off and back flush through the thermostat cavity. Back flushing sometimes clears the problem blockage. The fact that there is no thermostat could indicate that the previous owner had a cooling problem.

Re: 1967 6hp Johnson Overheating

The old impeller was not broken apart, it seperated from the brass coupling and was not turning with it. I replaced the whole water pump as to not take a chance. I also back washed through the area the thermostat should have been. Water came out fairly strong. I noticed though that there is now a oil/wtare type residue everywhere in the middle and lower unit area. I am now wondering if the head gasket is blown and/or a bad grommet for the water tube going into the power head. Thats where Im confused. Water comes out of the exhaust and appears to be getting through the cooling lines. But after 2-3minutes WOT it starts slowing down and overheating. After cooling for a while it restarts and runs ok in idle or half throttle.

Re: 1967 6hp Johnson Overheating

with no thermostat the water runs thru the motor so fast, that the convection, to remove the heat does not happen. as said above, check the compression, as you could have blown a head or exhaust gasket, causing it to over heat. and put a thermostat in it.