1959 10hp Johnson Seahorse

[ryan.mn5]

I recently bought an old 1959 Johnson Seahorse for basically dirt cheap. Ran it for a couple days no problem, but then I couldn't get it running anymore. Took it apart and ended up realigning the mag points, as well as replacing plug wires. After confirming I had good spark, I tried to get it running. Started up decently well, but would only run for about 30-45 seconds before overheating and stalling. I replaced the impeller because I had a spare and then ensured that the water pump was properly connected to the water tube which it was. I started it up again and the same thing happened, running for about 30-45 seconds only to overheat and stall. Could this just be an old corroded thermostat? Please help!

 

[racerone]

Just 3 screws let you look at / inspect the thermostat.---A very common thermostat used for many years into the 1990's model motors.

 

[lindy46]

How do you know it's overheating? Is water coming out of the exhaust port on the back of the motor? Have you checked the temperature of the head?

 

[oldboat1]

Thinking there might be an obstruction in the intake, or in the water channels somewhere. Bits and pieces of an old impeller, maybe. An old t.stat would probably be stuck (corroded) open -- probably not a source for overheating but should be replaced. There are other issues, I think. With the t.stat out see if the water is reaching that point. If mine, I would remove the head cover and check for blockages -- clear them if any found. If a salt water motor look for hardened salt build up. If a river runner look for sand or other debris.

If new to motors, are you adding oil to the gas? 24:1 would be the ratio for a '59. Like Lindy says, be sure it's overheating (cylinder tops too hot to touch is a good clue).

 

[ryan.mn5]

The thermostat is in rough condition, with a good amount of corrosion and almost nothing left of the gasket that was there, however I'm not quite sure how to tell if it is stuck open or closed. There is little to no water coming out of the exhaust port on the back of the motor, as well as minimal water reaching the thermostat. I assumed it was overheating because the motor was almost to hot to even touch, however I have not checked the temperature of the head. I am kind of new to tinkering with outboard motors and this website, so I really appreciate the fast replies and ideas! I will be ordering a new thermostat and definitely checking for hardened salt build up in the head cover because its a salt water motor. Also I have been running it with 24:1 oil to gas ratio which is indeed what the manual indicated for a '59.

 

[oldboat1]

Good project. The blockage would be in the water passages around the cylinders (typically), so with the cover off you would use a knife or similar tool to scrape it out (then flush). Pretty much wherever you find a blockage. With the t.stat and lower unit removed, try pushing some water up the tube to clear -- also down from the t.stat opening.

 

[racerone]

If you can not put your hand on the motor it is overheating.----Or if water sprinkled on the cylinder head sizzles , it is too hot.-------The water tube was properly installed in the upper grommet first when you installed the lower unit I hope.----You do have the water level 6 to 8" above the pump when testing I hope.

 

[tjandrews]

You might want to make sure the impeller drive pin in the drive shaft is actually engaging the impeller, or even that it's still there. Those pins are tiny, and easily lost. (Don't ask how I know this.)