1948 Johnson HD25 Overheats

[Dizzy Weasel]

Folks,

I have a 1948 seahorse HD25 - runs like a clock (now) but overheats. I replaced the impeller, when I remove the brass water plug at the bottom of the motor water pours out, when I put it back in the motor seems to lug down. I know it must be plugged up internally somewhere but not sure where to look first. I pulled off the head and the power unit but things look OK (have not taken the carb/exhaust cover off yet). Is there a diagram or does anybody know what path the water takes through the motor and/or where it is most likely plugged?

Thanks,

DW

 

[seahorse5]

Re: 1948 Johnson HD25 Overheats

debris behind the exhaust cover is most likely the culprit

 

[Dizzy Weasel]

Re: 1948 Johnson HD25 Overheats

Took the carb/exhaust plate off last night - everything is clear. The gasket between the carb/water housing and the flat plate looked pretty tattered - maybe exhaust pressure leaking into water side is creating a "bubble" in the motor that the pump can't over come?

Thanks,

DW

 

[RogersJetboat454]

Re: 1948 Johnson HD25 Overheats

Folks,

I have a 1948 seahorse HD25 - runs like a clock (now) but overheats. I replaced the impeller, when I remove the brass water plug at the bottom of the motor water pours out, when I put it back in the motor seems to lug down. I know it must be plugged up internally somewhere but not sure where to look first. I pulled off the head and the power unit but things look OK (have not taken the carb/exhaust cover off yet). Is there a diagram or does anybody know what path the water takes through the motor and/or where it is most likely plugged?

Thanks,

DW

Welcome to Iboats Dizzy Weasel.

I don't know much about these engines, but I have a friend of mine with the exact same motor and issue you are having. If he figures out what the problem is, I will let you know.

Actually... if he figures out the problem, you will know, because you are him.
Good luck Mr. Weasel. Hopefully someone can give you some hints.

 

[HighTrim]

Re: 1948 Johnson HD25 Overheats

Is this issue happening on a boat underway or in a test barrel?

 

[Dizzy Weasel]

Re: 1948 Johnson HD25 Overheats

Overheats underway. I have not tried it on the lake since I replaced the "tattered" gasket I found.