1957 johnson 7.5hp overheating question

[jbjennings]

Guys,
I got a nice lower unit and midsection for my '57 7.5hp johnson, and it has a good impeller wear plate and good impeller, but doesn't stay cool. In spite of the fact that lots of water is coming out of the exhaust relief---just as much as my good '57 evinrude 7.5hp, it is getting hot. According to my infrared thermometer, the bottom cylinder is quite a bit hotter than the top---175 degrees on the bottom and 157 on top. I don't know if it would keep climbing because that's as hot as I wanted to risk it, but I suspect it would. Could there be a clogged water jacket passage that would still let water get to the exhaust relief, but bypass part of the powerhead? I'm unsure where to look for the problem.
Thanks for any suggestions,
JBJ

 

[AlTn]

Re: 1957 johnson 7.5hp overheating question

exhaust entering the water jacket from the head gasket or exhaust gasket can cause an over heating issue...don't know the liklihood of this though

 

[jbjennings]

Re: 1957 johnson 7.5hp overheating question

Thanks AlTn,
I rechecked it with a new barrel of water and I'm hoping that the problem was due to the water just being too darned hot in the barrel. It's about a 100 degrees here lately and that barrel water must have been at least that hot, because it felt more than warm. I'm going to try it on the lake and check it there, and if not, replace the exhaust gaskets as you suggested.
Thanks for the help,
JBJ